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https://dev.mysql.com/doc/refman/8.4/en/flush.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="flush">
</a>
15.7.8.3 FLUSH Statement
</h4>
</div>
</div>
</div>
<a class="indexterm" name="idm46045168794768">
</a>
<a class="indexterm" name="idm46045168793696">
</a>
<a class="indexterm" name="idm46045168792624">
</a>
<a class="indexterm" name="idm46045168791136">
</a>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa84528549"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">FLUSH</span> <span class="token punctuation">[</span><span class="token keyword">NO_WRITE_TO_BINLOG</span> <span class="token operator">|</span> <span class="token keyword">LOCAL</span><span class="token punctuation">]</span> {
<em class="replaceable">flush_option</em> <span class="token punctuation">[</span><span class="token punctuation">,</span> <em class="replaceable">flush_option</em><span class="token punctuation">]</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token operator">|</span> <em class="replaceable">tables_option</em>
}
<em class="replaceable">flush_option</em>: {
<span class="token datatype">BINARY</span> <span class="token keyword">LOGS</span>
<span class="token operator">|</span> <span class="token keyword">ENGINE</span> <span class="token keyword">LOGS</span>
<span class="token operator">|</span> <span class="token keyword">ERROR</span> <span class="token keyword">LOGS</span>
<span class="token operator">|</span> <span class="token keyword">GENERAL</span> <span class="token keyword">LOGS</span>
<span class="token operator">|</span> <span class="token keyword">LOGS</span>
<span class="token operator">|</span> <span class="token keyword">PRIVILEGES</span>
<span class="token operator">|</span> <span class="token keyword">OPTIMIZER_COSTS</span>
<span class="token operator">|</span> <span class="token keyword">RELAY</span> <span class="token keyword">LOGS</span> <span class="token punctuation">[</span><span class="token keyword">FOR</span> <span class="token keyword">CHANNEL</span> <span class="token keyword"><em class="replaceable">channel</em></span><span class="token punctuation">]</span>
<span class="token operator">|</span> <span class="token keyword">SLOW</span> <span class="token keyword">LOGS</span>
<span class="token operator">|</span> <span class="token keyword">STATUS</span>
<span class="token operator">|</span> <span class="token keyword">USER_RESOURCES</span>
}
<em class="replaceable">tables_option</em>: {
<em class="replaceable">table_synonym</em>
<span class="token operator">|</span> <em class="replaceable">table_synonym</em> <em class="replaceable">tbl_name</em> <span class="token punctuation">[</span><span class="token punctuation">,</span> <em class="replaceable">tbl_name</em><span class="token punctuation">]</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token operator">|</span> <em class="replaceable">table_synonym</em> <span class="token keyword">WITH</span> <span class="token keyword">READ</span> <span class="token keyword">LOCK</span>
<span class="token operator">|</span> <em class="replaceable">table_synonym</em> <em class="replaceable">tbl_name</em> <span class="token punctuation">[</span><span class="token punctuation">,</span> <em class="replaceable">tbl_name</em><span class="token punctuation">]</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span> <span class="token keyword">WITH</span> <span class="token keyword">READ</span> <span class="token keyword">LOCK</span>
<span class="token operator">|</span> <em class="replaceable">table_synonym</em> <em class="replaceable">tbl_name</em> <span class="token punctuation">[</span><span class="token punctuation">,</span> <em class="replaceable">tbl_name</em><span class="token punctuation">]</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span> <span class="token keyword">FOR</span> <span class="token keyword">EXPORT</span>
}
<em class="replaceable">table_synonym</em>: {
<span class="token keyword">TABLE</span>
<span class="token operator">|</span> <span class="token keyword">TABLES</span>
}</code></pre>
</div>
<p>
The
<a class="link" href="flush.html" title="15.7.8.3 FLUSH Statement">
<code class="literal">
FLUSH
</code>
</a>
statement has several
variant forms that clear or reload various internal caches,
flush tables, or acquire locks. Each
<a class="link" href="flush.html" title="15.7.8.3 FLUSH Statement">
<code class="literal">
FLUSH
</code>
</a>
operation requires the
privileges indicated in its description.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
It is not possible to issue
<a class="link" href="flush.html" title="15.7.8.3 FLUSH Statement">
<code class="literal">
FLUSH
</code>
</a>
statements within stored
functions or triggers. However, you may use
<a class="link" href="flush.html" title="15.7.8.3 FLUSH Statement">
<code class="literal">
FLUSH
</code>
</a>
in stored procedures, so
long as these are not called from stored functions or
triggers. See
<a class="xref" href="stored-program-restrictions.html" title="27.8 Restrictions on Stored Programs">
Section 27.8, “Restrictions on Stored Programs”
</a>
.
</p>
</div>
<p>
By default, the server writes
<a class="link" href="flush.html" title="15.7.8.3 FLUSH Statement">
<code class="literal">
FLUSH
</code>
</a>
statements to the binary
log so that they replicate to replicas. To suppress logging,
specify the optional
<code class="literal">
NO_WRITE_TO_BINLOG
</code>
keyword or its alias
<code class="literal">
LOCAL
</code>
.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
<a class="link" href="flush.html#flush-logs">
<code class="literal">
FLUSH LOGS
</code>
</a>
,
<a class="link" href="flush.html#flush-binary-logs">
<code class="literal">
FLUSH BINARY LOGS
</code>
</a>
,
<a class="link" href="flush.html#flush-tables-with-read-lock">
<code class="literal">
FLUSH TABLES WITH READ LOCK
</code>
</a>
(with or without a table list), and
<a class="link" href="flush.html#flush-tables-for-export-with-list">
<code class="literal">
FLUSH
TABLES
<em class="replaceable">
<code>
tbl_name
</code>
</em>
... FOR
EXPORT
</code>
</a>
are not written to the binary log in any case
because they would cause problems if replicated to a replica.
</p>
</div>
<p>
The
<a class="link" href="flush.html" title="15.7.8.3 FLUSH Statement">
<code class="literal">
FLUSH
</code>
</a>
statement causes an
implicit commit. See
<a class="xref" href="implicit-commit.html" title="15.3.3 Statements That Cause an Implicit Commit">
Section 15.3.3, “Statements That Cause an Implicit Commit”
</a>
.
</p>
<p>
The
<a class="link" href="mysqladmin.html" title="6.5.2 mysqladmin — A MySQL Server Administration Program">
<span class="command">
<strong>
mysqladmin
</strong>
</span>
</a>
utility provides a
command-line interface to some flush operations, using commands
such as
<code class="literal">
flush-logs
</code>
,
<code class="literal">
flush-privileges
</code>
,
<code class="literal">
flush-status
</code>
, and
<code class="literal">
flush-tables
</code>
. See
<a class="xref" href="mysqladmin.html" title="6.5.2 mysqladmin — A MySQL Server Administration Program">
Section 6.5.2, “mysqladmin — A MySQL Server Administration Program”
</a>
.
</p>
<a class="indexterm" name="idm46045168753088">
</a>
<a class="indexterm" name="idm46045168751600">
</a>
<p>
Sending a
<code class="literal">
SIGHUP
</code>
or
<code class="literal">
SIGUSR1
</code>
signal to the server causes several
flush operations to occur that are similar to various forms of
the
<a class="link" href="flush.html" title="15.7.8.3 FLUSH Statement">
<code class="literal">
FLUSH
</code>
</a>
statement. Signals can
be sent by the
<code class="literal">
root
</code>
system account or the
system account that owns the server process. This enables the
flush operations to be performed without having to connect to
the server, which requires a MySQL account that has privileges
sufficient for those operations. See
<a class="xref" href="unix-signal-response.html" title="6.10 Unix Signal Handling in MySQL">
Section 6.10, “Unix Signal Handling in MySQL”
</a>
.
</p>
<p>
The
<a class="link" href="reset.html" title="15.7.8.6 RESET Statement">
<code class="literal">
RESET
</code>
</a>
statement is similar to
<a class="link" href="flush.html" title="15.7.8.3 FLUSH Statement">
<code class="literal">
FLUSH
</code>
</a>
. See
<a class="xref" href="reset.html" title="15.7.8.6 RESET Statement">
Section 15.7.8.6, “RESET Statement”
</a>
, for information about using
<a class="link" href="reset.html" title="15.7.8.6 RESET Statement">
<code class="literal">
RESET
</code>
</a>
with replication.
</p>
<p>
The following list describes the permitted
<a class="link" href="flush.html" title="15.7.8.3 FLUSH Statement">
<code class="literal">
FLUSH
</code>
</a>
statement
<em class="replaceable">
<code>
flush_option
</code>
</em>
values. For descriptions
of the permitted
<em class="replaceable">
<code>
tables_option
</code>
</em>
values, see
<a class="xref" href="flush.html#flush-tables-variants" title="FLUSH TABLES Syntax">
FLUSH TABLES Syntax
</a>
.
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<a name="flush-binary-logs">
</a>
<a class="link" href="flush.html#flush-binary-logs">
<code class="literal">
FLUSH BINARY LOGS
</code>
</a>
</p>
<p>
Closes and reopens any binary log file to which the server
is writing. If binary logging is enabled, the sequence
number of the binary log file is incremented by one relative
to the previous file.
</p>
<p>
This operation requires the
<a class="link" href="privileges-provided.html#priv_reload">
<code class="literal">
RELOAD
</code>
</a>
privilege.
</p>
</li>
<li class="listitem">
<p>
<a name="flush-engine-logs">
</a>
<a class="link" href="flush.html#flush-engine-logs">
<code class="literal">
FLUSH ENGINE LOGS
</code>
</a>
</p>
<p>
Closes and reopens any flushable logs for installed storage
engines. This causes
<code class="literal">
InnoDB
</code>
to flush its
logs to disk.
</p>
<p>
This operation requires the
<a class="link" href="privileges-provided.html#priv_reload">
<code class="literal">
RELOAD
</code>
</a>
privilege.
</p>
</li>
<li class="listitem">
<p>
<a name="flush-error-logs">
</a>
<a class="link" href="flush.html#flush-error-logs">
<code class="literal">
FLUSH ERROR LOGS
</code>
</a>
</p>
<p>
Closes and reopens any error log file to which the server is
writing.
</p>
<p>
This operation requires the
<a class="link" href="privileges-provided.html#priv_reload">
<code class="literal">
RELOAD
</code>
</a>
privilege.
</p>
</li>
<li class="listitem">
<p>
<a name="flush-general-logs">
</a>
<a class="link" href="flush.html#flush-general-logs">
<code class="literal">
FLUSH GENERAL LOGS
</code>
</a>
</p>
<p>
Closes and reopens any general query log file to which the
server is writing.
</p>
<p>
This operation requires the
<a class="link" href="privileges-provided.html#priv_reload">
<code class="literal">
RELOAD
</code>
</a>
privilege.
</p>
<p>
This operation has no effect on tables used for the general
query log (see
<a class="xref" href="log-destinations.html" title="7.4.1 Selecting General Query Log and Slow Query Log Output Destinations">
Section 7.4.1, “Selecting General Query Log and Slow Query Log Output Destinations”
</a>
).
</p>
</li>
<li class="listitem">
<p>
<a name="flush-logs">
</a>
<a class="link" href="flush.html#flush-logs">
<code class="literal">
FLUSH LOGS
</code>
</a>
</p>
<p>
Closes and reopens any log file to which the server is
writing.
</p>
<p>
This operation requires the
<a class="link" href="privileges-provided.html#priv_reload">
<code class="literal">
RELOAD
</code>
</a>
privilege.
</p>
<p>
The effect of this operation is equivalent to the combined
effects of these operations:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa7362494"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">FLUSH</span> <span class="token datatype">BINARY</span> <span class="token keyword">LOGS</span>
<span class="token keyword">FLUSH</span> <span class="token keyword">ENGINE</span> <span class="token keyword">LOGS</span>
<span class="token keyword">FLUSH</span> <span class="token keyword">ERROR</span> <span class="token keyword">LOGS</span>
<span class="token keyword">FLUSH</span> <span class="token keyword">GENERAL</span> <span class="token keyword">LOGS</span>
<span class="token keyword">FLUSH</span> <span class="token keyword">RELAY</span> <span class="token keyword">LOGS</span>
<span class="token keyword">FLUSH</span> <span class="token keyword">SLOW</span> <span class="token keyword">LOGS</span></code></pre>
</div>
</li>
<li class="listitem">
<p>
<a name="flush-optimizer-costs">
</a>
<a class="link" href="flush.html#flush-optimizer-costs">
<code class="literal">
FLUSH OPTIMIZER_COSTS
</code>
</a>
</p>
<p>
Re-reads the cost model tables so that the optimizer starts
using the current cost estimates stored in them.
</p>
<p>
This operation requires the
<a class="link" href="privileges-provided.html#priv_flush-optimizer-costs">
<code class="literal">
FLUSH_OPTIMIZER_COSTS
</code>
</a>
or
<a class="link" href="privileges-provided.html#priv_reload">
<code class="literal">
RELOAD
</code>
</a>
privilege.
</p>
<p>
The server writes a warning to the error log for any
unrecognized cost model table entries. For information about
these tables, see
<a class="xref" href="cost-model.html" title="10.9.5 The Optimizer Cost Model">
Section 10.9.5, “The Optimizer Cost Model”
</a>
. This
operation affects only sessions that begin subsequent to the
flush. Existing sessions continue to use the cost estimates
that were current when they began.
</p>
</li>
<li class="listitem">
<p>
<a name="flush-privileges">
</a>
<a class="link" href="flush.html#flush-privileges">
<code class="literal">
FLUSH PRIVILEGES
</code>
</a>
</p>
<p>
Re-reads the privileges from the grant tables in the
<code class="literal">
mysql
</code>
system schema. As part of this
operation, the server reads the
<code class="literal">
global_grants
</code>
table containing dynamic
privilege assignments and registers any unregistered
privileges found there.
</p>
<p>
Reloading the grant tables is necessary to enable updates to
MySQL privileges and users only if you make such changes
directly to the grant tables; it is not needed for account
management statements such as
<a class="link" href="grant.html" title="15.7.1.6 GRANT Statement">
<code class="literal">
GRANT
</code>
</a>
or
<a class="link" href="revoke.html" title="15.7.1.8 REVOKE Statement">
<code class="literal">
REVOKE
</code>
</a>
, which take effect
immediately. See
<a class="xref" href="privilege-changes.html" title="8.2.13 When Privilege Changes Take Effect">
Section 8.2.13, “When Privilege Changes Take Effect”
</a>
, for
more information.
</p>
<p>
This operation requires the
<a class="link" href="privileges-provided.html#priv_reload">
<code class="literal">
RELOAD
</code>
</a>
or
<a class="link" href="privileges-provided.html#priv_flush-privileges">
<code class="literal">
FLUSH_PRIVILEGES
</code>
</a>
privilege.
</p>
<p>
If the
<a class="link" href="server-options.html#option_mysqld_skip-grant-tables">
<code class="option">
--skip-grant-tables
</code>
</a>
option was specified at server startup to disable the MySQL
privilege system,
<a class="link" href="flush.html#flush-privileges">
<code class="literal">
FLUSH
PRIVILEGES
</code>
</a>
provides a way to enable the privilege
system at runtime.
</p>
<p>
Resets failed-login tracking (or enables it if the server
was started with
<a class="link" href="server-options.html#option_mysqld_skip-grant-tables">
<code class="option">
--skip-grant-tables
</code>
</a>
) and
unlocks any temporarily locked accounts. See
<a class="xref" href="password-management.html" title="8.2.15 Password Management">
Section 8.2.15, “Password Management”
</a>
.
</p>
<p>
Frees memory cached by the server as a result of
<a class="link" href="grant.html" title="15.7.1.6 GRANT Statement">
<code class="literal">
GRANT
</code>
</a>
,
<a class="link" href="create-user.html" title="15.7.1.3 CREATE USER Statement">
<code class="literal">
CREATE USER
</code>
</a>
,
<a class="link" href="create-server.html" title="15.1.18 CREATE SERVER Statement">
<code class="literal">
CREATE SERVER
</code>
</a>
, and
<a class="link" href="install-plugin.html" title="15.7.4.4 INSTALL PLUGIN Statement">
<code class="literal">
INSTALL PLUGIN
</code>
</a>
statements.
This memory is not released by the corresponding
<a class="link" href="revoke.html" title="15.7.1.8 REVOKE Statement">
<code class="literal">
REVOKE
</code>
</a>
,
<a class="link" href="drop-user.html" title="15.7.1.5 DROP USER Statement">
<code class="literal">
DROP USER
</code>
</a>
,
<a class="link" href="drop-server.html" title="15.1.30 DROP SERVER Statement">
<code class="literal">
DROP SERVER
</code>
</a>
, and
<a class="link" href="uninstall-plugin.html" title="15.7.4.6 UNINSTALL PLUGIN Statement">
<code class="literal">
UNINSTALL PLUGIN
</code>
</a>
statements,
so for a server that executes many instances of the
statements that cause caching, there is an increase in
cached memory use unless it is freed with
<a class="link" href="flush.html#flush-privileges">
<code class="literal">
FLUSH PRIVILEGES
</code>
</a>
.
</p>
<p>
Clears the in-memory cache used by the
<code class="literal">
caching_sha2_password
</code>
authentication
plugin. See
<a class="xref" href="caching-sha2-pluggable-authentication.html#caching-sha2-pluggable-authentication-cache-operation" title="Cache Operation for SHA-2 Pluggable Authentication">
Cache Operation for SHA-2 Pluggable Authentication
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a name="flush-relay-logs">
</a>
<a class="link" href="flush.html#flush-relay-logs">
<code class="literal">
FLUSH
RELAY LOGS [FOR CHANNEL
<em class="replaceable">
<code>
channel
</code>
</em>
]
</code>
</a>
</p>
<p>
Closes and reopens any relay log file to which the server is
writing. If relay logging is enabled, the sequence number of
the relay log file is incremented by one relative to the
previous file.
</p>
<p>
This operation requires the
<a class="link" href="privileges-provided.html#priv_reload">
<code class="literal">
RELOAD
</code>
</a>
privilege.
</p>
<p>
The
<code class="literal">
FOR CHANNEL
<em class="replaceable">
<code>
channel
</code>
</em>
</code>
clause enables
you to name which replication channel the operation applies
to. Execute
<a class="link" href="flush.html#flush-relay-logs">
<code class="literal">
FLUSH
RELAY LOGS FOR CHANNEL
<em class="replaceable">
<code>
channel
</code>
</em>
</code>
</a>
to flush the
relay log for a specific replication channel. If no channel
is named and no extra replication channels exist, the
operation applies to the default channel. If no channel is
named and multiple replication channels exist, the operation
applies to all replication channels. For more information,
see
<a class="xref" href="replication-channels.html" title="19.2.2 Replication Channels">
Section 19.2.2, “Replication Channels”
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a name="flush-slow-logs">
</a>
<a class="link" href="flush.html#flush-slow-logs">
<code class="literal">
FLUSH SLOW LOGS
</code>
</a>
</p>
<p>
Closes and reopens any slow query log file to which the
server is writing.
</p>
<p>
This operation requires the
<a class="link" href="privileges-provided.html#priv_reload">
<code class="literal">
RELOAD
</code>
</a>
privilege.
</p>
<p>
This operation has no effect on tables used for the slow
query log (see
<a class="xref" href="log-destinations.html" title="7.4.1 Selecting General Query Log and Slow Query Log Output Destinations">
Section 7.4.1, “Selecting General Query Log and Slow Query Log Output Destinations”
</a>
).
</p>
</li>
<li class="listitem">
<p>
<a name="flush-status">
</a>
<a class="link" href="flush.html#flush-status">
<code class="literal">
FLUSH STATUS
</code>
</a>
</p>
<p>
Flushes status indicators.
</p>
<p>
This operation adds the current thread's session status
variable values to the global values and resets the session
values to zero. Some global variables may be reset to zero
as well. It also resets the counters for key caches (default
and named) to zero and sets
<a class="link" href="server-status-variables.html#statvar_Max_used_connections">
<code class="literal">
Max_used_connections
</code>
</a>
to
the current number of open connections. This information may
be of use when debugging a query. See
<a class="xref" href="bug-reports.html" title="1.6 How to Report Bugs or Problems">
Section 1.6, “How to Report Bugs or Problems”
</a>
.
</p>
<p>
<code class="literal">
FLUSH STATUS
</code>
is unaffected by
<a class="link" href="server-system-variables.html#sysvar_read_only">
<code class="literal">
read_only
</code>
</a>
or
<a class="link" href="server-system-variables.html#sysvar_super_read_only">
<code class="literal">
super_read_only
</code>
</a>
, and is
always written to the binary log.
</p>
<p>
This operation requires the
<a class="link" href="privileges-provided.html#priv_flush-status">
<code class="literal">
FLUSH_STATUS
</code>
</a>
or
<a class="link" href="privileges-provided.html#priv_reload">
<code class="literal">
RELOAD
</code>
</a>
privilege.
</p>
</li>
<li class="listitem">
<p>
<a name="flush-user-resources">
</a>
<a class="link" href="flush.html#flush-user-resources">
<code class="literal">
FLUSH USER_RESOURCES
</code>
</a>
</p>
<p>
Resets all per-hour user resource indicators to zero.
</p>
<p>
This operation requires the
<a class="link" href="privileges-provided.html#priv_flush-user-resources">
<code class="literal">
FLUSH_USER_RESOURCES
</code>
</a>
or
<a class="link" href="privileges-provided.html#priv_reload">
<code class="literal">
RELOAD
</code>
</a>
privilege.
</p>
<p>
Resetting resource indicators enables clients that have
reached their hourly connection, query, or update limits to
resume activity immediately.
<a class="link" href="flush.html#flush-user-resources">
<code class="literal">
FLUSH
USER_RESOURCES
</code>
</a>
does not apply to the limit on
maximum simultaneous connections that is controlled by the
<a class="link" href="server-system-variables.html#sysvar_max_user_connections">
<code class="literal">
max_user_connections
</code>
</a>
system
variable. See
<a class="xref" href="user-resources.html" title="8.2.21 Setting Account Resource Limits">
Section 8.2.21, “Setting Account Resource Limits”
</a>
.
</p>
</li>
</ul>
</div>
<h5>
<a name="flush-tables-variants">
</a>
FLUSH TABLES Syntax
</h5>
<p>
<a class="link" href="flush.html#flush-tables">
<code class="literal">
FLUSH TABLES
</code>
</a>
flushes tables, and,
depending on the variant used, acquires locks. Any
<code class="literal">
TABLES
</code>
variant used in a
<a class="link" href="flush.html" title="15.7.8.3 FLUSH Statement">
<code class="literal">
FLUSH
</code>
</a>
statement must be the only
option used.
<a class="link" href="flush.html#flush-tables">
<code class="literal">
FLUSH
TABLE
</code>
</a>
is a synonym for
<a class="link" href="flush.html#flush-tables">
<code class="literal">
FLUSH
TABLES
</code>
</a>
.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
The descriptions here that indicate tables are flushed by
closing them apply differently for
<code class="literal">
InnoDB
</code>
,
which flushes table contents to disk but leaves them open.
This still permits table files to be copied while the tables
are open, as long as other activity does not modify them.
</p>
</div>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<a name="flush-tables">
</a>
<a class="link" href="flush.html#flush-tables">
<code class="literal">
FLUSH TABLES
</code>
</a>
</p>
<p>
Closes all open tables, forces all tables in use to be
closed, and flushes the prepared statement cache.
</p>
<p>
This operation requires the
<a class="link" href="privileges-provided.html#priv_flush-tables">
<code class="literal">
FLUSH_TABLES
</code>
</a>
or
<a class="link" href="privileges-provided.html#priv_reload">
<code class="literal">
RELOAD
</code>
</a>
privilege.
</p>
<p>
For information about prepared statement caching, see
<a class="xref" href="statement-caching.html" title="10.10.3 Caching of Prepared Statements and Stored Programs">
Section 10.10.3, “Caching of Prepared Statements and Stored Programs”
</a>
.
</p>
<p>
<a class="link" href="flush.html#flush-tables">
<code class="literal">
FLUSH TABLES
</code>
</a>
is not permitted
when there is an active
<a class="link" href="lock-tables.html" title="15.3.6 LOCK TABLES and UNLOCK TABLES Statements">
<code class="literal">
LOCK TABLES ...
READ
</code>
</a>
. To flush and lock tables, use
<a class="link" href="flush.html#flush-tables-with-read-lock-with-list">
<code class="literal">
FLUSH
TABLES
<em class="replaceable">
<code>
tbl_name
</code>
</em>
... WITH READ
LOCK
</code>
</a>
instead.
</p>
</li>
<li class="listitem">
<p>
<a name="flush-tables-with-list">
</a>
<a class="link" href="flush.html#flush-tables-with-list">
<code class="literal">
FLUSH
TABLES
<em class="replaceable">
<code>
tbl_name
</code>
</em>
[,
<em class="replaceable">
<code>
tbl_name
</code>
</em>
] ...
</code>
</a>
</p>
<p>
With a list of one or more comma-separated table names, this
operation is like
<a class="link" href="flush.html#flush-tables">
<code class="literal">
FLUSH
TABLES
</code>
</a>
with no names except that the server
flushes only the named tables. If a named table does not
exist, no error occurs.
</p>
<p>
This operation requires the
<a class="link" href="privileges-provided.html#priv_flush-tables">
<code class="literal">
FLUSH_TABLES
</code>
</a>
or
<a class="link" href="privileges-provided.html#priv_reload">
<code class="literal">
RELOAD
</code>
</a>
privilege.
</p>
</li>
<li class="listitem">
<p>
<a name="flush-tables-with-read-lock">
</a>
<a class="link" href="flush.html#flush-tables-with-read-lock">
<code class="literal">
FLUSH
TABLES WITH READ LOCK
</code>
</a>
</p>
<p>
Closes all open tables and locks all tables for all
databases with a global read lock.
</p>
<p>
This operation requires the
<a class="link" href="privileges-provided.html#priv_flush-tables">
<code class="literal">
FLUSH_TABLES
</code>
</a>
or
<a class="link" href="privileges-provided.html#priv_reload">
<code class="literal">
RELOAD
</code>
</a>
privilege.
</p>
<p>
This operation is a very convenient way to get backups if
you have a file system such as Veritas or ZFS that can take
snapshots in time. Use
<a class="link" href="lock-tables.html" title="15.3.6 LOCK TABLES and UNLOCK TABLES Statements">
<code class="literal">
UNLOCK
TABLES
</code>
</a>
to release the lock.
</p>
<p>
<a class="link" href="flush.html#flush-tables-with-read-lock">
<code class="literal">
FLUSH TABLES WITH READ LOCK
</code>
</a>
acquires a global read lock rather than table locks, so it
is not subject to the same behavior as
<a class="link" href="lock-tables.html" title="15.3.6 LOCK TABLES and UNLOCK TABLES Statements">
<code class="literal">
LOCK TABLES
</code>
</a>
and
<a class="link" href="lock-tables.html" title="15.3.6 LOCK TABLES and UNLOCK TABLES Statements">
<code class="literal">
UNLOCK
TABLES
</code>
</a>
with respect to table locking and implicit
commits:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<p>
<a class="link" href="lock-tables.html" title="15.3.6 LOCK TABLES and UNLOCK TABLES Statements">
<code class="literal">
UNLOCK
TABLES
</code>
</a>
implicitly commits any active
transaction only if any tables currently have been
locked with
<a class="link" href="lock-tables.html" title="15.3.6 LOCK TABLES and UNLOCK TABLES Statements">
<code class="literal">
LOCK TABLES
</code>
</a>
.
The commit does not occur for
<a class="link" href="lock-tables.html" title="15.3.6 LOCK TABLES and UNLOCK TABLES Statements">
<code class="literal">
UNLOCK
TABLES
</code>
</a>
following
<a class="link" href="flush.html#flush-tables-with-read-lock">
<code class="literal">
FLUSH
TABLES WITH READ LOCK
</code>
</a>
because the latter
statement does not acquire table locks.
</p>
</li>
<li class="listitem">
<p>
Beginning a transaction causes table locks acquired with
<a class="link" href="lock-tables.html" title="15.3.6 LOCK TABLES and UNLOCK TABLES Statements">
<code class="literal">
LOCK TABLES
</code>
</a>
to be
released, as though you had executed
<a class="link" href="lock-tables.html" title="15.3.6 LOCK TABLES and UNLOCK TABLES Statements">
<code class="literal">
UNLOCK
TABLES
</code>
</a>
. Beginning a transaction does not
release a global read lock acquired with
<a class="link" href="flush.html#flush-tables-with-read-lock">
<code class="literal">
FLUSH TABLES WITH READ
LOCK
</code>
</a>
.
</p>
</li>
</ul>
</div>
<p>
<a class="link" href="flush.html#flush-tables-with-read-lock">
<code class="literal">
FLUSH TABLES WITH READ LOCK
</code>
</a>
does not prevent the server from inserting rows into the log
tables (see
<a class="xref" href="log-destinations.html" title="7.4.1 Selecting General Query Log and Slow Query Log Output Destinations">
Section 7.4.1, “Selecting General Query Log and Slow Query Log Output Destinations”
</a>
).
</p>
</li>
<li class="listitem">
<p>
<a name="flush-tables-with-read-lock-with-list">
</a>
<a class="link" href="flush.html#flush-tables-with-read-lock-with-list">
<code class="literal">
FLUSH
TABLES
<em class="replaceable">
<code>
tbl_name
</code>
</em>
[,
<em class="replaceable">
<code>
tbl_name
</code>
</em>
] ... WITH READ
LOCK
</code>
</a>
</p>
<p>
Flushes and acquires read locks for the named tables.
</p>
<p>
This operation requires the
<a class="link" href="privileges-provided.html#priv_flush-tables">
<code class="literal">
FLUSH_TABLES
</code>
</a>
or
<a class="link" href="privileges-provided.html#priv_reload">
<code class="literal">
RELOAD
</code>
</a>
privilege. Because it
acquires table locks, it also requires the
<a class="link" href="privileges-provided.html#priv_lock-tables">
<code class="literal">
LOCK TABLES
</code>
</a>
privilege for
each table.
</p>
<p>
The operation first acquires exclusive metadata locks for
the tables, so it waits for transactions that have those
tables open to complete. Then the operation flushes the
tables from the table cache, reopens the tables, acquires
table locks (like
<a class="link" href="lock-tables.html" title="15.3.6 LOCK TABLES and UNLOCK TABLES Statements">
<code class="literal">
LOCK TABLES ...
READ
</code>
</a>
), and downgrades the metadata locks from
exclusive to shared. After the operation acquires locks and
downgrades the metadata locks, other sessions can read but
not modify the tables.
</p>
<p>
This operation applies only to existing base
(non-
<code class="literal">
TEMPORARY)
</code>
tables. If a name refers
to a base table, that table is used. If it refers to a
<code class="literal">
TEMPORARY
</code>
table, it is ignored. If a name
applies to a view, an
<a class="ulink" href="/doc/mysql-errors/8.4/en/server-error-reference.html#error_er_wrong_object" target="_top">
<code class="literal">
ER_WRONG_OBJECT
</code>
</a>
error
occurs. Otherwise, an
<a class="ulink" href="/doc/mysql-errors/8.4/en/server-error-reference.html#error_er_no_such_table" target="_top">
<code class="literal">
ER_NO_SUCH_TABLE
</code>
</a>
error
occurs.
</p>
<p>
Use
<a class="link" href="lock-tables.html" title="15.3.6 LOCK TABLES and UNLOCK TABLES Statements">
<code class="literal">
UNLOCK
TABLES
</code>
</a>
to release the locks,
<a class="link" href="lock-tables.html" title="15.3.6 LOCK TABLES and UNLOCK TABLES Statements">
<code class="literal">
LOCK TABLES
</code>
</a>
to release the
locks and acquire other locks, or
<a class="link" href="commit.html" title="15.3.1 START TRANSACTION, COMMIT, and ROLLBACK Statements">
<code class="literal">
START
TRANSACTION
</code>
</a>
to release the locks and begin a new
transaction.
</p>
<p>
This
<a class="link" href="flush.html#flush-tables">
<code class="literal">
FLUSH TABLES
</code>
</a>
variant
enables tables to be flushed and locked in a single
operation. It provides a workaround for the restriction that
<a class="link" href="flush.html#flush-tables">
<code class="literal">
FLUSH TABLES
</code>
</a>
is not permitted
when there is an active
<a class="link" href="lock-tables.html" title="15.3.6 LOCK TABLES and UNLOCK TABLES Statements">
<code class="literal">
LOCK TABLES ...
READ
</code>
</a>
.
</p>
<p>
This operation does not perform an implicit
<a class="link" href="lock-tables.html" title="15.3.6 LOCK TABLES and UNLOCK TABLES Statements">
<code class="literal">
UNLOCK
TABLES
</code>
</a>
, so an error results if you perform the
operation while there is any active
<a class="link" href="lock-tables.html" title="15.3.6 LOCK TABLES and UNLOCK TABLES Statements">
<code class="literal">
LOCK TABLES
</code>
</a>
or use it a
second time without first releasing the locks acquired.
</p>
<p>
If a flushed table was opened with
<a class="link" href="handler.html" title="15.2.5 HANDLER Statement">
<code class="literal">
HANDLER
</code>
</a>
, the handler is
implicitly flushed and loses its position.
</p>
</li>
<li class="listitem">
<p>
<a name="flush-tables-for-export-with-list">
</a>
<a class="link" href="flush.html#flush-tables-for-export-with-list">
<code class="literal">
FLUSH
TABLES
<em class="replaceable">
<code>
tbl_name
</code>
</em>
[,
<em class="replaceable">
<code>
tbl_name
</code>
</em>
] ... FOR
EXPORT
</code>
</a>
</p>
<p>
This
<a class="link" href="flush.html#flush-tables">
<code class="literal">
FLUSH TABLES
</code>
</a>
variant
applies to
<code class="literal">
InnoDB
</code>
tables. It ensures that
changes to the named tables have been flushed to disk so
that binary table copies can be made while the server is
running.
</p>
<p>
This operation requires the
<a class="link" href="privileges-provided.html#priv_flush-tables">
<code class="literal">
FLUSH_TABLES
</code>
</a>
or
<a class="link" href="privileges-provided.html#priv_reload">
<code class="literal">
RELOAD
</code>
</a>
privilege. Because it
acquires locks on tables in preparation for exporting them,
it also requires the
<a class="link" href="privileges-provided.html#priv_lock-tables">
<code class="literal">
LOCK
TABLES
</code>
</a>
and
<a class="link" href="privileges-provided.html#priv_select">
<code class="literal">
SELECT
</code>
</a>
privileges for each table.
</p>
<p>
The operation works like this:
</p>
<div class="orderedlist">
<ol class="orderedlist" type="1">
<li class="listitem">
<p>
It acquires shared metadata locks for the named tables.
The operation blocks as long as other sessions have
active transactions that have modified those tables or
hold table locks for them. When the locks have been
acquired, the operation blocks transactions that attempt
to update the tables, while permitting read-only
operations to continue.
</p>
</li>
<li class="listitem">
<p>
It checks whether all storage engines for the tables
support
<code class="literal">
FOR EXPORT
</code>
. If any do not, an
<a class="ulink" href="/doc/mysql-errors/8.4/en/server-error-reference.html#error_er_illegal_ha" target="_top">
<code class="literal">
ER_ILLEGAL_HA
</code>
</a>
error
occurs and the operation fails.
</p>
</li>
<li class="listitem">
<p>
The operation notifies the storage engine for each table
to make the table ready for export. The storage engine
must ensure that any pending changes are written to
disk.
</p>
</li>
<li class="listitem">
<p>
The operation puts the session in lock-tables mode so
that the metadata locks acquired earlier are not
released when the
<code class="literal">
FOR EXPORT
</code>
operation completes.
</p>
</li>
</ol>
</div>
<p>
This operation applies only to existing base
(non-
<code class="literal">
TEMPORARY
</code>
) tables. If a name refers
to a base table, that table is used. If it refers to a
<code class="literal">
TEMPORARY
</code>
table, it is ignored. If a name
applies to a view, an
<a class="ulink" href="/doc/mysql-errors/8.4/en/server-error-reference.html#error_er_wrong_object" target="_top">
<code class="literal">
ER_WRONG_OBJECT
</code>
</a>
error
occurs. Otherwise, an
<a class="ulink" href="/doc/mysql-errors/8.4/en/server-error-reference.html#error_er_no_such_table" target="_top">
<code class="literal">
ER_NO_SUCH_TABLE
</code>
</a>
error
occurs.
</p>
<p>
<code class="literal">
InnoDB
</code>
supports
<code class="literal">
FOR
EXPORT
</code>
for tables that have their own
<a class="link" href="glossary.html#glos_ibd_file" title=".ibd file">
<code class="filename">
.ibd
</code>
file
</a>
file (that is, tables created with the
<a class="link" href="innodb-parameters.html#sysvar_innodb_file_per_table">
<code class="literal">
innodb_file_per_table
</code>
</a>
setting enabled).
<code class="literal">
InnoDB
</code>
ensures when
notified by the
<code class="literal">
FOR EXPORT
</code>
operation that
any changes have been flushed to disk. This permits a binary
copy of table contents to be made while the
<code class="literal">
FOR
EXPORT
</code>
operation is in effect because the
<code class="filename">
.ibd
</code>
file is transaction consistent and
can be copied while the server is running.
<code class="literal">
FOR
EXPORT
</code>
does not apply to
<code class="literal">
InnoDB
</code>
system tablespace files, or to
<code class="literal">
InnoDB
</code>
tables that have
<code class="literal">
FULLTEXT
</code>
indexes.
</p>
<p>
<a class="link" href="flush.html#flush-tables-for-export-with-list">
<code class="literal">
FLUSH
TABLES ...FOR EXPORT
</code>
</a>
is supported for partitioned
<code class="literal">
InnoDB
</code>
tables.
</p>
<p>
When notified by
<code class="literal">
FOR EXPORT
</code>
,
<code class="literal">
InnoDB
</code>
writes to disk certain kinds of
data that is normally held in memory or in separate disk
buffers outside the tablespace files. For each table,
<code class="literal">
InnoDB
</code>
also produces a file named
<code class="filename">
<em class="replaceable">
<code>
table_name
</code>
</em>
.cfg
</code>
in the same database directory as the table. The
<code class="filename">
.cfg
</code>
file contains metadata needed to
reimport the tablespace files later, into the same or
different server.
</p>
<p>
When the
<code class="literal">
FOR EXPORT
</code>
operation completes,
<code class="literal">
InnoDB
</code>
has flushed all
<a class="link" href="glossary.html#glos_dirty_page" title="dirty page">
dirty pages
</a>
to the
table data files. Any
<a class="link" href="glossary.html#glos_change_buffer" title="change buffer">
change buffer
</a>
entries are merged prior to flushing. At this point, the
tables are locked and quiescent: The tables are in a
transactionally consistent state on disk and you can copy
the
<code class="filename">
.ibd
</code>
tablespace files along with
the corresponding
<code class="filename">
.cfg
</code>
files to get a
consistent snapshot of those tables.
</p>
<p>
For the procedure to reimport the copied table data into a
MySQL instance, see
<a class="xref" href="innodb-table-import.html" title="17.6.1.3 Importing InnoDB Tables">
Section 17.6.1.3, “Importing InnoDB Tables”
</a>
.
</p>
<p>
After you are done with the tables, use
<a class="link" href="lock-tables.html" title="15.3.6 LOCK TABLES and UNLOCK TABLES Statements">
<code class="literal">
UNLOCK
TABLES
</code>
</a>
to release the locks,
<a class="link" href="lock-tables.html" title="15.3.6 LOCK TABLES and UNLOCK TABLES Statements">
<code class="literal">
LOCK TABLES
</code>
</a>
to release the
locks and acquire other locks, or
<a class="link" href="commit.html" title="15.3.1 START TRANSACTION, COMMIT, and ROLLBACK Statements">
<code class="literal">
START
TRANSACTION
</code>
</a>
to release the locks and begin a new
transaction.
</p>
<p>
While any of these statements is in effect within the
session, attempts to use
<a class="link" href="flush.html#flush-tables-for-export-with-list">
<code class="literal">
FLUSH
TABLES ... FOR EXPORT
</code>
</a>
produce an error:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa15088486"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">FLUSH</span> <span class="token keyword">TABLES</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span> <span class="token keyword">WITH</span> <span class="token keyword">READ</span> <span class="token keyword">LOCK</span>
<span class="token keyword">FLUSH</span> <span class="token keyword">TABLES</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span> <span class="token keyword">FOR</span> <span class="token keyword">EXPORT</span>
<span class="token keyword">LOCK</span> <span class="token keyword">TABLES</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span> <span class="token keyword">READ</span>
<span class="token keyword">LOCK</span> <span class="token keyword">TABLES</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span> <span class="token keyword">WRITE</span></code></pre>
</div>
<p>
While
<a class="link" href="flush.html#flush-tables-for-export-with-list">
<code class="literal">
FLUSH
TABLES ... FOR EXPORT
</code>
</a>
is in effect within the
session, attempts to use any of these statements produce an
error:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa32517033"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">FLUSH</span> <span class="token keyword">TABLES</span> <span class="token keyword">WITH</span> <span class="token keyword">READ</span> <span class="token keyword">LOCK</span>
<span class="token keyword">FLUSH</span> <span class="token keyword">TABLES</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span> <span class="token keyword">WITH</span> <span class="token keyword">READ</span> <span class="token keyword">LOCK</span>
<span class="token keyword">FLUSH</span> <span class="token keyword">TABLES</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span> <span class="token keyword">FOR</span> <span class="token keyword">EXPORT</span></code></pre>
</div>
</li>
</ul>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/general-security-issues.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h2 class="title">
<a name="general-security-issues">
</a>
8.1 General Security Issues
</h2>
</div>
</div>
</div>
<div class="toc">
<dl class="toc">
<dt>
<span class="section">
<a href="security-guidelines.html">
8.1.1 Security Guidelines
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="password-security.html">
8.1.2 Keeping Passwords Secure
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="security-against-attack.html">
8.1.3 Making MySQL Secure Against Attackers
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="security-options.html">
8.1.4 Security-Related mysqld Options and Variables
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="changing-mysql-user.html">
8.1.5 How to Run MySQL as a Normal User
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="load-data-local-security.html">
8.1.6 Security Considerations for LOAD DATA LOCAL
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="secure-client-programming.html">
8.1.7 Client Programming Security Guidelines
</a>
</span>
</dt>
</dl>
</div>
<a class="indexterm" name="idm46045252952800">
</a>
<p>
This section describes general security issues to be aware of and
what you can do to make your MySQL installation more secure against
attack or misuse. For information specifically about the access
control system that MySQL uses for setting up user accounts and
checking database access, see
<a class="xref" href="postinstallation.html" title="2.9 Postinstallation Setup and Testing">
Section 2.9, “Postinstallation Setup and Testing”
</a>
.
</p>
<p>
For answers to some questions that are often asked about MySQL
Server security issues, see
<a class="xref" href="faqs-security.html" title="A.9 MySQL 8.4 FAQ: Security">
Section A.9, “MySQL 8.4 FAQ: Security”
</a>
.
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/innodb-information-schema-understanding-innodb-locking.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="innodb-information-schema-understanding-innodb-locking">
</a>
17.15.2.2 InnoDB Lock and Lock-Wait Information
</h4>
</div>
</div>
</div>
<p>
When a transaction updates a row in a table, or locks it with
<code class="literal">
SELECT FOR UPDATE
</code>
,
<code class="literal">
InnoDB
</code>
establishes a list or queue of locks on that row. Similarly,
<code class="literal">
InnoDB
</code>
maintains a list of locks on a table
for table-level locks. If a second transaction wants to update a
row or lock a table already locked by a prior transaction in an
incompatible mode,
<code class="literal">
InnoDB
</code>
adds a lock request
for the row to the corresponding queue. For a lock to be
acquired by a transaction, all incompatible lock requests
previously entered into the lock queue for that row or table
must be removed (which occurs when the transactions holding or
requesting those locks either commit or roll back).
</p>
<p>
A transaction may have any number of lock requests for different
rows or tables. At any given time, a transaction may request a
lock that is held by another transaction, in which case it is
blocked by that other transaction. The requesting transaction
must wait for the transaction that holds the blocking lock to
commit or roll back. If a transaction is not waiting for a lock,
it is in a
<code class="literal">
RUNNING
</code>
state. If a transaction is
waiting for a lock, it is in a
<code class="literal">
LOCK WAIT
</code>
state. (The
<code class="literal">
INFORMATION_SCHEMA
</code>
<a class="link" href="information-schema-innodb-trx-table.html" title="28.4.28 The INFORMATION_SCHEMA INNODB_TRX Table">
<code class="literal">
INNODB_TRX
</code>
</a>
table indicates
transaction state values.)
</p>
<p>
The Performance Schema
<a class="link" href="performance-schema-data-locks-table.html" title="29.12.13.1 The data_locks Table">
<code class="literal">
data_locks
</code>
</a>
table holds one or more rows for each
<code class="literal">
LOCK
WAIT
</code>
transaction, indicating any lock requests that
prevent its progress. This table also contains one row
describing each lock in a queue of locks pending for a given row
or table. The Performance Schema
<a class="link" href="performance-schema-data-lock-waits-table.html" title="29.12.13.2 The data_lock_waits Table">
<code class="literal">
data_lock_waits
</code>
</a>
table shows which
locks already held by a transaction are blocking locks requested
by other transactions.
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/innodb-locking.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="innodb-locking">
</a>
17.7.1 InnoDB Locking
</h3>
</div>
</div>
</div>
<a class="indexterm" name="idm46045164599232">
</a>
<a class="indexterm" name="idm46045164597840">
</a>
<a class="indexterm" name="idm46045164596448">
</a>
<a class="indexterm" name="idm46045164595056">
</a>
<a class="indexterm" name="idm46045164593664">
</a>
<a class="indexterm" name="idm46045164592272">
</a>
<a class="indexterm" name="idm46045164590880">
</a>
<a class="indexterm" name="idm46045164589488">
</a>
<a class="indexterm" name="idm46045164588096">
</a>
<a class="indexterm" name="idm46045164586704">
</a>
<a class="indexterm" name="idm46045164585312">
</a>
<a class="indexterm" name="idm46045164584304">
</a>
<a class="indexterm" name="idm46045164583296">
</a>
<a class="indexterm" name="idm46045164582288">
</a>
<a class="indexterm" name="idm46045164581280">
</a>
<a class="indexterm" name="idm46045164580272">
</a>
<a class="indexterm" name="idm46045164579264">
</a>
<p>
This section describes lock types used by
<code class="literal">
InnoDB
</code>
.
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<a class="xref" href="innodb-locking.html#innodb-shared-exclusive-locks" title="Shared and Exclusive Locks">
Shared and Exclusive Locks
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="innodb-locking.html#innodb-intention-locks" title="Intention Locks">
Intention Locks
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="innodb-locking.html#innodb-record-locks" title="Record Locks">
Record Locks
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="innodb-locking.html#innodb-gap-locks" title="Gap Locks">
Gap Locks
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="innodb-locking.html#innodb-next-key-locks" title="Next-Key Locks">
Next-Key Locks
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="innodb-locking.html#innodb-insert-intention-locks" title="Insert Intention Locks">
Insert Intention Locks
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="innodb-locking.html#innodb-auto-inc-locks" title="AUTO-INC Locks">
AUTO-INC Locks
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="innodb-locking.html#innodb-predicate-locks" title="Predicate Locks for Spatial Indexes">
Predicate Locks for Spatial Indexes
</a>
</p>
</li>
</ul>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h4 class="title">
<a name="innodb-shared-exclusive-locks">
</a>
Shared and Exclusive Locks
</h4>
</div>
</div>
</div>
<p>
<code class="literal">
InnoDB
</code>
implements standard row-level locking
where there are two types of locks,
<a class="link" href="glossary.html#glos_shared_lock" title="shared lock">
shared (
<code class="literal">
S
</code>
)
locks
</a>
and
<a class="link" href="glossary.html#glos_exclusive_lock" title="exclusive lock">
exclusive
(
<code class="literal">
X
</code>
) locks
</a>
.
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
A
<a class="link" href="glossary.html#glos_shared_lock" title="shared lock">
shared
(
<code class="literal">
S
</code>
) lock
</a>
permits the transaction
that holds the lock to read a row.
</p>
</li>
<li class="listitem">
<p>
An
<a class="link" href="glossary.html#glos_exclusive_lock" title="exclusive lock">
exclusive
(
<code class="literal">
X
</code>
) lock
</a>
permits the transaction
that holds the lock to update or delete a row.
</p>
</li>
</ul>
</div>
<p>
If transaction
<code class="literal">
T1
</code>
holds a shared
(
<code class="literal">
S
</code>
) lock on row
<code class="literal">
r
</code>
, then
requests from some distinct transaction
<code class="literal">
T2
</code>
for a lock on row
<code class="literal">
r
</code>
are handled as follows:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
A request by
<code class="literal">
T2
</code>
for an
<code class="literal">
S
</code>
lock can be granted immediately. As a
result, both
<code class="literal">
T1
</code>
and
<code class="literal">
T2
</code>
hold an
<code class="literal">
S
</code>
lock on
<code class="literal">
r
</code>
.
</p>
</li>
<li class="listitem">
<p>
A request by
<code class="literal">
T2
</code>
for an
<code class="literal">
X
</code>
lock cannot be granted immediately.
</p>
</li>
</ul>
</div>
<p>
If a transaction
<code class="literal">
T1
</code>
holds an exclusive
(
<code class="literal">
X
</code>
) lock on row
<code class="literal">
r
</code>
, a
request from some distinct transaction
<code class="literal">
T2
</code>
for
a lock of either type on
<code class="literal">
r
</code>
cannot be granted
immediately. Instead, transaction
<code class="literal">
T2
</code>
has to
wait for transaction
<code class="literal">
T1
</code>
to release its lock
on row
<code class="literal">
r
</code>
.
</p>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h4 class="title">
<a name="innodb-intention-locks">
</a>
Intention Locks
</h4>
</div>
</div>
</div>
<p>
<code class="literal">
InnoDB
</code>
supports
<span class="emphasis">
<em>
multiple
granularity locking
</em>
</span>
which permits coexistence of row
locks and table locks. For example, a statement such as
<a class="link" href="lock-tables.html" title="15.3.6 LOCK TABLES and UNLOCK TABLES Statements">
<code class="literal">
LOCK TABLES ...
WRITE
</code>
</a>
takes an exclusive lock (an
<code class="literal">
X
</code>
lock) on the specified table. To make locking at multiple
granularity levels practical,
<code class="literal">
InnoDB
</code>
uses
<a class="link" href="glossary.html#glos_intention_lock" title="intention lock">
intention locks
</a>
.
Intention locks are table-level locks that indicate which type
of lock (shared or exclusive) a transaction requires later for a
row in a table. There are two types of intention locks:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
An
<a class="link" href="glossary.html#glos_intention_shared_lock" title="intention shared lock">
intention
shared lock
</a>
(
<code class="literal">
IS
</code>
) indicates that a
transaction intends to set a
<span class="emphasis">
<em>
shared
</em>
</span>
lock on individual rows in a table.
</p>
</li>
<li class="listitem">
<p>
An
<a class="link" href="glossary.html#glos_intention_exclusive_lock" title="intention exclusive lock">
intention
exclusive lock
</a>
(
<code class="literal">
IX
</code>
) indicates that
a transaction intends to set an exclusive lock on individual
rows in a table.
</p>
</li>
</ul>
</div>
<p>
For example,
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT ...
FOR SHARE
</code>
</a>
sets an
<code class="literal">
IS
</code>
lock, and
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT ... FOR
UPDATE
</code>
</a>
sets an
<code class="literal">
IX
</code>
lock.
</p>
<p>
The intention locking protocol is as follows:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
Before a transaction can acquire a shared lock on a row in a
table, it must first acquire an
<code class="literal">
IS
</code>
lock
or stronger on the table.
</p>
</li>
<li class="listitem">
<p>
Before a transaction can acquire an exclusive lock on a row
in a table, it must first acquire an
<code class="literal">
IX
</code>
lock on the table.
</p>
</li>
</ul>
</div>
<p>
Table-level lock type compatibility is summarized in the
following matrix.
</p>
<div class="informaltable">
<table summary='A matrix showing table-level lock type compatibility. Each cell in the matrix is marked as either "Compatible" or "Conflict".'>
<colgroup>
<col style="width: 20%"/>
<col style="width: 20%"/>
<col style="width: 20%"/>
<col style="width: 20%"/>
<col style="width: 20%"/>
</colgroup>
<thead>
<tr>
<th scope="col">
</th>
<th scope="col">
<code class="literal">
X
</code>
</th>
<th scope="col">
<code class="literal">
IX
</code>
</th>
<th scope="col">
<code class="literal">
S
</code>
</th>
<th scope="col">
<code class="literal">
IS
</code>
</th>
</tr>
</thead>
<tbody>
<tr>
<th scope="row">
<code class="literal">
X
</code>
</th>
<td>
Conflict
</td>
<td>
Conflict
</td>
<td>
Conflict
</td>
<td>
Conflict
</td>
</tr>
<tr>
<th scope="row">
<code class="literal">
IX
</code>
</th>
<td>
Conflict
</td>
<td>
Compatible
</td>
<td>
Conflict
</td>
<td>
Compatible
</td>
</tr>
<tr>
<th scope="row">
<code class="literal">
S
</code>
</th>
<td>
Conflict
</td>
<td>
Conflict
</td>
<td>
Compatible
</td>
<td>
Compatible
</td>
</tr>
<tr>
<th scope="row">
<code class="literal">
IS
</code>
</th>
<td>
Conflict
</td>
<td>
Compatible
</td>
<td>
Compatible
</td>
<td>
Compatible
</td>
</tr>
</tbody>
</table>
</div>
<p>
A lock is granted to a requesting transaction if it is
compatible with existing locks, but not if it conflicts with
existing locks. A transaction waits until the conflicting
existing lock is released. If a lock request conflicts with an
existing lock and cannot be granted because it would cause
<a class="link" href="glossary.html#glos_deadlock" title="deadlock">
deadlock
</a>
, an error occurs.
</p>
<p>
Intention locks do not block anything except full table requests
(for example,
<a class="link" href="lock-tables.html" title="15.3.6 LOCK TABLES and UNLOCK TABLES Statements">
<code class="literal">
LOCK
TABLES ... WRITE
</code>
</a>
). The main purpose of intention locks
is to show that someone is locking a row, or going to lock a row
in the table.
</p>
<p>
Transaction data for an intention lock appears similar to the
following in
<a class="link" href="show-engine.html" title="15.7.7.16 SHOW ENGINE Statement">
<code class="literal">
SHOW
ENGINE INNODB STATUS
</code>
</a>
and
<a class="link" href="innodb-standard-monitor.html" title="17.17.3 InnoDB Standard Monitor and Lock Monitor Output">
InnoDB monitor
</a>
output:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-terminal"><div class="docs-select-all right" id="sa24208817"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-terminal">TABLE LOCK table `test`<span class="token punctuation">.</span>`t` trx id 10080 lock mode IX</code></pre>
</div>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h4 class="title">
<a name="innodb-record-locks">
</a>
Record Locks
</h4>
</div>
</div>
</div>
<p>
A record lock is a lock on an index record. For example,
<code class="literal">
SELECT c1 FROM t WHERE c1 = 10 FOR UPDATE;
</code>
prevents any other transaction from inserting, updating, or
deleting rows where the value of
<code class="literal">
t.c1
</code>
is
<code class="literal">
10
</code>
.
</p>
<p>
Record locks always lock index records, even if a table is
defined with no indexes. For such cases,
<code class="literal">
InnoDB
</code>
creates a hidden clustered index and
uses this index for record locking. See
<a class="xref" href="innodb-index-types.html" title="17.6.2.1 Clustered and Secondary Indexes">
Section 17.6.2.1, “Clustered and Secondary Indexes”
</a>
.
</p>
<p>
Transaction data for a record lock appears similar to the
following in
<a class="link" href="show-engine.html" title="15.7.7.16 SHOW ENGINE Statement">
<code class="literal">
SHOW
ENGINE INNODB STATUS
</code>
</a>
and
<a class="link" href="innodb-standard-monitor.html" title="17.17.3 InnoDB Standard Monitor and Lock Monitor Output">
InnoDB monitor
</a>
output:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-terminal"><div class="docs-select-all right" id="sa67687606"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-terminal">RECORD LOCKS space id 58 page no 3 n bits 72 index `PRIMARY` of table `test`<span class="token punctuation">.</span>`t`
trx id 10078 lock_mode X locks rec but not gap
Record lock<span class="token punctuation">,</span> heap no 2 PHYSICAL RECORD<span class="token punctuation">:</span> n_fields 3<span class="token punctuation">;</span> compact format<span class="token punctuation">;</span> info bits 0
0<span class="token punctuation">:</span> len 4<span class="token punctuation">;</span> hex 8000000a<span class="token punctuation">;</span> asc <span class="token punctuation">;</span><span class="token punctuation">;</span>
1<span class="token punctuation">:</span> len 6<span class="token punctuation">;</span> hex 00000000274f<span class="token punctuation">;</span> asc 'O<span class="token punctuation">;</span><span class="token punctuation">;</span>
2<span class="token punctuation">:</span> len 7<span class="token punctuation">;</span> hex b60000019d0110<span class="token punctuation">;</span> asc <span class="token punctuation">;</span><span class="token punctuation">;</span></code></pre>
</div>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h4 class="title">
<a name="innodb-gap-locks">
</a>
Gap Locks
</h4>
</div>
</div>
</div>
<p>
A gap lock is a lock on a gap between index records, or a lock
on the gap before the first or after the last index record. For
example,
<code class="literal">
SELECT c1 FROM t WHERE c1 BETWEEN 10 and 20
FOR UPDATE;
</code>
prevents other transactions from inserting
a value of
<code class="literal">
15
</code>
into column
<code class="literal">
t.c1
</code>
, whether or not there was already any
such value in the column, because the gaps between all existing
values in the range are locked.
</p>
<p>
A gap might span a single index value, multiple index values, or
even be empty.
</p>
<p>
Gap locks are part of the tradeoff between performance and
concurrency, and are used in some transaction isolation levels
and not others.
</p>
<p>
Gap locking is not needed for statements that lock rows using a
unique index to search for a unique row. (This does not include
the case that the search condition includes only some columns of
a multiple-column unique index; in that case, gap locking does
occur.) For example, if the
<code class="literal">
id
</code>
column has a
unique index, the following statement uses only an index-record
lock for the row having
<code class="literal">
id
</code>
value 100 and it
does not matter whether other sessions insert rows in the
preceding gap:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa12918314"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> child <span class="token keyword">WHERE</span> id <span class="token operator">=</span> <span class="token number">100</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
If
<code class="literal">
id
</code>
is not indexed or has a nonunique
index, the statement does lock the preceding gap.
</p>
<p>
It is also worth noting here that conflicting locks can be held
on a gap by different transactions. For example, transaction A
can hold a shared gap lock (gap S-lock) on a gap while
transaction B holds an exclusive gap lock (gap X-lock) on the
same gap. The reason conflicting gap locks are allowed is that
if a record is purged from an index, the gap locks held on the
record by different transactions must be merged.
</p>
<p>
Gap locks in
<code class="literal">
InnoDB
</code>
are
<span class="quote">
“
<span class="quote">
purely
inhibitive
</span>
”
</span>
, which means that their only purpose is to
prevent other transactions from inserting to the gap. Gap locks
can co-exist. A gap lock taken by one transaction does not
prevent another transaction from taking a gap lock on the same
gap. There is no difference between shared and exclusive gap
locks. They do not conflict with each other, and they perform
the same function.
</p>
<p>
Gap locking can be disabled explicitly. This occurs if you
change the transaction isolation level to
<a class="link" href="innodb-transaction-isolation-levels.html#isolevel_read-committed">
<code class="literal">
READ COMMITTED
</code>
</a>
. In this case,
gap locking is disabled for searches and index scans and is used
only for foreign-key constraint checking and duplicate-key
checking.
</p>
<p>
There are also other effects of using the
<a class="link" href="innodb-transaction-isolation-levels.html#isolevel_read-committed">
<code class="literal">
READ COMMITTED
</code>
</a>
isolation
level. Record locks for nonmatching rows are released after
MySQL has evaluated the
<code class="literal">
WHERE
</code>
condition. For
<code class="literal">
UPDATE
</code>
statements,
<code class="literal">
InnoDB
</code>
does a
<span class="quote">
“
<span class="quote">
semi-consistent
</span>
”
</span>
read, such that it returns
the latest committed version to MySQL so that MySQL can
determine whether the row matches the
<code class="literal">
WHERE
</code>
condition of the
<a class="link" href="update.html" title="15.2.17 UPDATE Statement">
<code class="literal">
UPDATE
</code>
</a>
.
</p>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h4 class="title">
<a name="innodb-next-key-locks">
</a>
Next-Key Locks
</h4>
</div>
</div>
</div>
<p>
A next-key lock is a combination of a record lock on the index
record and a gap lock on the gap before the index record.
</p>
<p>
<code class="literal">
InnoDB
</code>
performs row-level locking in such a
way that when it searches or scans a table index, it sets shared
or exclusive locks on the index records it encounters. Thus, the
row-level locks are actually index-record locks. A next-key lock
on an index record also affects the
<span class="quote">
“
<span class="quote">
gap
</span>
”
</span>
before
that index record. That is, a next-key lock is an index-record
lock plus a gap lock on the gap preceding the index record. If
one session has a shared or exclusive lock on record
<code class="literal">
R
</code>
in an index, another session cannot insert
a new index record in the gap immediately before
<code class="literal">
R
</code>
in the index order.
</p>
<p>
Suppose that an index contains the values 10, 11, 13, and 20.
The possible next-key locks for this index cover the following
intervals, where a round bracket denotes exclusion of the
interval endpoint and a square bracket denotes inclusion of the
endpoint:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-none"><div class="docs-select-all right" id="sa72484878"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-none">(negative infinity, 10]
(10, 11]
(11, 13]
(13, 20]
(20, positive infinity)</code></pre>
</div>
<p>
For the last interval, the next-key lock locks the gap above the
largest value in the index and the
<span class="quote">
“
<span class="quote">
supremum
</span>
”
</span>
pseudo-record having a value higher than any value actually in
the index. The supremum is not a real index record, so, in
effect, this next-key lock locks only the gap following the
largest index value.
</p>
<p>
By default,
<code class="literal">
InnoDB
</code>
operates in
<a class="link" href="innodb-transaction-isolation-levels.html#isolevel_repeatable-read">
<code class="literal">
REPEATABLE READ
</code>
</a>
transaction
isolation level. In this case,
<code class="literal">
InnoDB
</code>
uses
next-key locks for searches and index scans, which prevents
phantom rows (see
<a class="xref" href="innodb-next-key-locking.html" title="17.7.4 Phantom Rows">
Section 17.7.4, “Phantom Rows”
</a>
).
</p>
<p>
Transaction data for a next-key lock appears similar to the
following in
<a class="link" href="show-engine.html" title="15.7.7.16 SHOW ENGINE Statement">
<code class="literal">
SHOW
ENGINE INNODB STATUS
</code>
</a>
and
<a class="link" href="innodb-standard-monitor.html" title="17.17.3 InnoDB Standard Monitor and Lock Monitor Output">
InnoDB monitor
</a>
output:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-terminal"><div class="docs-select-all right" id="sa52427616"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-terminal">RECORD LOCKS space id 58 page no 3 n bits 72 index `PRIMARY` of table `test`<span class="token punctuation">.</span>`t`
trx id 10080 lock_mode X
Record lock<span class="token punctuation">,</span> heap no 1 PHYSICAL RECORD<span class="token punctuation">:</span> n_fields 1<span class="token punctuation">;</span> compact format<span class="token punctuation">;</span> info bits 0
0<span class="token punctuation">:</span> len 8<span class="token punctuation">;</span> hex 73757072656d756d<span class="token punctuation">;</span> asc supremum<span class="token punctuation">;</span><span class="token punctuation">;</span>
Record lock<span class="token punctuation">,</span> heap no 2 PHYSICAL RECORD<span class="token punctuation">:</span> n_fields 3<span class="token punctuation">;</span> compact format<span class="token punctuation">;</span> info bits 0
0<span class="token punctuation">:</span> len 4<span class="token punctuation">;</span> hex 8000000a<span class="token punctuation">;</span> asc <span class="token punctuation">;</span><span class="token punctuation">;</span>
1<span class="token punctuation">:</span> len 6<span class="token punctuation">;</span> hex 00000000274f<span class="token punctuation">;</span> asc 'O<span class="token punctuation">;</span><span class="token punctuation">;</span>
2<span class="token punctuation">:</span> len 7<span class="token punctuation">;</span> hex b60000019d0110<span class="token punctuation">;</span> asc <span class="token punctuation">;</span><span class="token punctuation">;</span></code></pre>
</div>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h4 class="title">
<a name="innodb-insert-intention-locks">
</a>
Insert Intention Locks
</h4>
</div>
</div>
</div>
<p>
An insert intention lock is a type of gap lock set by
<a class="link" href="insert.html" title="15.2.7 INSERT Statement">
<code class="literal">
INSERT
</code>
</a>
operations prior to row
insertion. This lock signals the intent to insert in such a way
that multiple transactions inserting into the same index gap
need not wait for each other if they are not inserting at the
same position within the gap. Suppose that there are index
records with values of 4 and 7. Separate transactions that
attempt to insert values of 5 and 6, respectively, each lock the
gap between 4 and 7 with insert intention locks prior to
obtaining the exclusive lock on the inserted row, but do not
block each other because the rows are nonconflicting.
</p>
<p>
The following example demonstrates a transaction taking an
insert intention lock prior to obtaining an exclusive lock on
the inserted record. The example involves two clients, A and B.
</p>
<p>
Client A creates a table containing two index records (90 and
102) and then starts a transaction that places an exclusive lock
on index records with an ID greater than 100. The exclusive lock
includes a gap lock before record 102:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa6855669"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> child <span class="token punctuation">(</span>id <span class="token datatype">int</span><span class="token punctuation">(</span><span class="token number">11</span><span class="token punctuation">)</span> <span class="token operator">NOT</span> <span class="token boolean">NULL</span><span class="token punctuation">,</span> <span class="token keyword">PRIMARY</span> <span class="token keyword">KEY</span><span class="token punctuation">(</span>id<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token keyword">ENGINE</span><span class="token operator">=</span>InnoDB<span class="token punctuation">;</span>
<span class="token prompt">mysql></span> <span class="token keyword">INSERT</span> <span class="token keyword">INTO</span> child <span class="token punctuation">(</span>id<span class="token punctuation">)</span> <span class="token keyword">values</span> <span class="token punctuation">(</span><span class="token number">90</span><span class="token punctuation">)</span><span class="token punctuation">,</span><span class="token punctuation">(</span><span class="token number">102</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token prompt">mysql></span> <span class="token keyword">START</span> <span class="token keyword">TRANSACTION</span><span class="token punctuation">;</span>
<span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> child <span class="token keyword">WHERE</span> id <span class="token operator">></span> <span class="token number">100</span> <span class="token keyword">FOR</span> <span class="token keyword">UPDATE</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> id <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> 102 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span></code></pre>
</div>
<p>
Client B begins a transaction to insert a record into the gap.
The transaction takes an insert intention lock while it waits to
obtain an exclusive lock.
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa94512897"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">START</span> <span class="token keyword">TRANSACTION</span><span class="token punctuation">;</span>
<span class="token prompt">mysql></span> <span class="token keyword">INSERT</span> <span class="token keyword">INTO</span> child <span class="token punctuation">(</span>id<span class="token punctuation">)</span> <span class="token keyword">VALUES</span> <span class="token punctuation">(</span><span class="token number">101</span><span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
Transaction data for an insert intention lock appears similar to
the following in
<a class="link" href="show-engine.html" title="15.7.7.16 SHOW ENGINE Statement">
<code class="literal">
SHOW ENGINE INNODB
STATUS
</code>
</a>
and
<a class="link" href="innodb-standard-monitor.html" title="17.17.3 InnoDB Standard Monitor and Lock Monitor Output">
InnoDB monitor
</a>
output:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-terminal"><div class="docs-select-all right" id="sa967990"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-terminal">RECORD LOCKS space id 31 page no 3 n bits 72 index `PRIMARY` of table `test`<span class="token punctuation">.</span>`child`
trx id 8731 lock_mode X locks gap before rec insert intention waiting
Record lock<span class="token punctuation">,</span> heap no 3 PHYSICAL RECORD<span class="token punctuation">:</span> n_fields 3<span class="token punctuation">;</span> compact format<span class="token punctuation">;</span> info bits 0
0<span class="token punctuation">:</span> len 4<span class="token punctuation">;</span> hex 80000066<span class="token punctuation">;</span> asc f<span class="token punctuation">;</span><span class="token punctuation">;</span>
1<span class="token punctuation">:</span> len 6<span class="token punctuation">;</span> hex 000000002215<span class="token punctuation">;</span> asc " <span class="token punctuation">;</span><span class="token punctuation">;</span>
2<span class="token punctuation">:</span> len 7<span class="token punctuation">;</span> hex 9000000172011c<span class="token punctuation">;</span> asc r <span class="token punctuation">;</span><span class="token punctuation">;</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span></code></pre>
</div>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h4 class="title">
<a name="innodb-auto-inc-locks">
</a>
AUTO-INC Locks
</h4>
</div>
</div>
</div>
<p>
An
<code class="literal">
AUTO-INC
</code>
lock is a special table-level
lock taken by transactions inserting into tables with
<code class="literal">
AUTO_INCREMENT
</code>
columns. In the simplest case,
if one transaction is inserting values into the table, any other
transactions must wait to do their own inserts into that table,
so that rows inserted by the first transaction receive
consecutive primary key values.
</p>
<p>
The
<a class="link" href="innodb-parameters.html#sysvar_innodb_autoinc_lock_mode">
<code class="literal">
innodb_autoinc_lock_mode
</code>
</a>
variable controls the algorithm used for auto-increment locking.
It allows you to choose how to trade off between predictable
sequences of auto-increment values and maximum concurrency for
insert operations.
</p>
<p>
For more information, see
<a class="xref" href="innodb-auto-increment-handling.html" title="17.6.1.6 AUTO_INCREMENT Handling in InnoDB">
Section 17.6.1.6, “AUTO_INCREMENT Handling in InnoDB”
</a>
.
</p>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h4 class="title">
<a name="innodb-predicate-locks">
</a>
Predicate Locks for Spatial Indexes
</h4>
</div>
</div>
</div>
<a class="indexterm" name="idm46045164423616">
</a>
<a class="indexterm" name="idm46045164422608">
</a>
<p>
<code class="literal">
InnoDB
</code>
supports
<code class="literal">
SPATIAL
</code>
indexing of columns containing spatial data (see
<a class="xref" href="optimizing-spatial-analysis.html" title="13.4.9 Optimizing Spatial Analysis">
Section 13.4.9, “Optimizing Spatial Analysis”
</a>
).
</p>
<p>
To handle locking for operations involving
<code class="literal">
SPATIAL
</code>
indexes, next-key locking does not
work well to support
<a class="link" href="innodb-transaction-isolation-levels.html#isolevel_repeatable-read">
<code class="literal">
REPEATABLE
READ
</code>
</a>
or
<a class="link" href="innodb-transaction-isolation-levels.html#isolevel_serializable">
<code class="literal">
SERIALIZABLE
</code>
</a>
transaction
isolation levels. There is no absolute ordering concept in
multidimensional data, so it is not clear which is the
<span class="quote">
“
<span class="quote">
next
</span>
”
</span>
key.
</p>
<p>
To enable support of isolation levels for tables with
<code class="literal">
SPATIAL
</code>
indexes,
<code class="literal">
InnoDB
</code>
uses predicate locks. A
<code class="literal">
SPATIAL
</code>
index
contains minimum bounding rectangle (MBR) values, so
<code class="literal">
InnoDB
</code>
enforces consistent read on the index
by setting a predicate lock on the MBR value used for a query.
Other transactions cannot insert or modify a row that would
match the query condition.
</p>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/stored-program-restrictions.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h2 class="title">
<a name="stored-program-restrictions">
</a>
27.8 Restrictions on Stored Programs
</h2>
</div>
</div>
</div>
<a class="indexterm" name="idm46045081274016">
</a>
<a class="indexterm" name="idm46045081272528">
</a>
<a class="indexterm" name="idm46045081271040">
</a>
<a class="indexterm" name="idm46045081269552">
</a>
<a class="indexterm" name="idm46045081268064">
</a>
<a class="indexterm" name="idm46045081266576">
</a>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<a class="xref" href="stored-program-restrictions.html#stored-routine-sql-restrictions" title="SQL Statements Not Permitted in Stored Routines">
SQL Statements Not Permitted in Stored Routines
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="stored-program-restrictions.html#stored-routines-function-restrictions" title="Restrictions for Stored Functions">
Restrictions for Stored Functions
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="stored-program-restrictions.html#stored-routines-trigger-restrictions" title="Restrictions for Triggers">
Restrictions for Triggers
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="stored-program-restrictions.html#stored-routine-name-conflicts" title="Name Conflicts within Stored Routines">
Name Conflicts within Stored Routines
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="stored-program-restrictions.html#stored-routines-replication-restrictions" title="Replication Considerations">
Replication Considerations
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="stored-program-restrictions.html#stored-routines-debugging-restrictions" title="Debugging Considerations">
Debugging Considerations
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="stored-program-restrictions.html#stored-routines-standard-restrictions" title="Unsupported Syntax from the SQL:2003 Standard">
Unsupported Syntax from the SQL:2003 Standard
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="stored-program-restrictions.html#stored-routines-concurrency-restrictions" title="Stored Routine Concurrency Considerations">
Stored Routine Concurrency Considerations
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="stored-program-restrictions.html#stored-routines-event-restrictions" title="Event Scheduler Restrictions">
Event Scheduler Restrictions
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="stored-program-restrictions.html#stored-routines-ndbcluster" title="Stored routines and triggers in NDB Cluster">
Stored routines and triggers in NDB Cluster
</a>
</p>
</li>
</ul>
</div>
<p>
These restrictions apply to the features described in
<a class="xref" href="stored-objects.html" title="Chapter 27 Stored Objects">
Chapter 27,
<i>
Stored Objects
</i>
</a>
.
</p>
<p>
Some of the restrictions noted here apply to all stored routines;
that is, both to stored procedures and stored functions. There are
also some
<a class="link" href="stored-program-restrictions.html#stored-routines-function-restrictions" title="Restrictions for Stored Functions">
restrictions
specific to stored functions
</a>
but not to stored procedures.
</p>
<p>
The restrictions for stored functions also apply to triggers.
There are also some
<a class="link" href="stored-program-restrictions.html#stored-routines-trigger-restrictions" title="Restrictions for Triggers">
restrictions
specific to triggers
</a>
.
</p>
<p>
The restrictions for stored procedures also apply to the
<a class="link" href="do.html" title="15.2.3 DO Statement">
<code class="literal">
DO
</code>
</a>
clause of Event Scheduler event
definitions. There are also some
<a class="link" href="stored-program-restrictions.html#stored-routines-event-restrictions" title="Event Scheduler Restrictions">
restrictions
specific to events
</a>
.
</p>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h3 class="title">
<a name="stored-routine-sql-restrictions">
</a>
SQL Statements Not Permitted in Stored Routines
</h3>
</div>
</div>
</div>
<p>
Stored routines cannot contain arbitrary SQL statements. The
following statements are not permitted:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
The locking statements
<a class="link" href="lock-tables.html" title="15.3.6 LOCK TABLES and UNLOCK TABLES Statements">
<code class="literal">
LOCK
TABLES
</code>
</a>
and
<a class="link" href="lock-tables.html" title="15.3.6 LOCK TABLES and UNLOCK TABLES Statements">
<code class="literal">
UNLOCK
TABLES
</code>
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a class="link" href="alter-view.html" title="15.1.11 ALTER VIEW Statement">
<code class="literal">
ALTER VIEW
</code>
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a class="link" href="load-data.html" title="15.2.9 LOAD DATA Statement">
<code class="literal">
LOAD DATA
</code>
</a>
and
<a class="link" href="load-xml.html" title="15.2.10 LOAD XML Statement">
<code class="literal">
LOAD XML
</code>
</a>
.
</p>
</li>
<li class="listitem">
<p>
SQL prepared statements
(
<a class="link" href="prepare.html" title="15.5.1 PREPARE Statement">
<code class="literal">
PREPARE
</code>
</a>
,
<a class="link" href="execute.html" title="15.5.2 EXECUTE Statement">
<code class="literal">
EXECUTE
</code>
</a>
,
<a class="link" href="deallocate-prepare.html" title="15.5.3 DEALLOCATE PREPARE Statement">
<code class="literal">
DEALLOCATE PREPARE
</code>
</a>
) can be
used in stored procedures, but not stored functions or
triggers. Thus, stored functions and triggers cannot use
dynamic SQL (where you construct statements as strings and
then execute them).
</p>
</li>
<li class="listitem">
<p>
Generally, statements not permitted in SQL prepared
statements are also not permitted in stored programs. For a
list of statements supported as prepared statements, see
<a class="xref" href="sql-prepared-statements.html" title="15.5 Prepared Statements">
Section 15.5, “Prepared Statements”
</a>
. Exceptions are
<a class="link" href="signal.html" title="15.6.7.5 SIGNAL Statement">
<code class="literal">
SIGNAL
</code>
</a>
,
<a class="link" href="resignal.html" title="15.6.7.4 RESIGNAL Statement">
<code class="literal">
RESIGNAL
</code>
</a>
, and
<a class="link" href="get-diagnostics.html" title="15.6.7.3 GET DIAGNOSTICS Statement">
<code class="literal">
GET DIAGNOSTICS
</code>
</a>
, which are
not permissible as prepared statements but are permitted in
stored programs.
</p>
</li>
<li class="listitem">
<p>
Because local variables are in scope only during stored
program execution, references to them are not permitted in
prepared statements created within a stored program.
Prepared statement scope is the current session, not the
stored program, so the statement could be executed after the
program ends, at which point the variables would no longer
be in scope. For example,
<code class="literal">
SELECT ... INTO
<em class="replaceable">
<code>
local_var
</code>
</em>
</code>
cannot be
used as a prepared statement. This restriction also applies
to stored procedure and function parameters. See
<a class="xref" href="prepare.html" title="15.5.1 PREPARE Statement">
Section 15.5.1, “PREPARE Statement”
</a>
.
</p>
</li>
<li class="listitem">
<p>
Within all stored programs (stored procedures and functions,
triggers, and events), the parser treats
<a class="link" href="commit.html" title="15.3.1 START TRANSACTION, COMMIT, and ROLLBACK Statements">
<code class="literal">
BEGIN
[WORK]
</code>
</a>
as the beginning of a
<a class="link" href="begin-end.html" title="15.6.1 BEGIN ... END Compound Statement">
<code class="literal">
BEGIN ...
END
</code>
</a>
block. To begin a transaction in this context,
use
<a class="link" href="commit.html" title="15.3.1 START TRANSACTION, COMMIT, and ROLLBACK Statements">
<code class="literal">
START
TRANSACTION
</code>
</a>
instead.
</p>
</li>
</ul>
</div>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h3 class="title">
<a name="stored-routines-function-restrictions">
</a>
Restrictions for Stored Functions
</h3>
</div>
</div>
</div>
<p>
The following additional statements or operations are not
permitted within stored functions. They are permitted within
stored procedures, except stored procedures that are invoked
from within a stored function or trigger. For example, if you
use
<a class="link" href="flush.html" title="15.7.8.3 FLUSH Statement">
<code class="literal">
FLUSH
</code>
</a>
in a stored procedure,
that stored procedure cannot be called from a stored function or
trigger.
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
Statements that perform explicit or implicit commit or
rollback. Support for these statements is not required by
the SQL standard, which states that each DBMS vendor may
decide whether to permit them.
</p>
</li>
<li class="listitem">
<p>
Statements that return a result set. This includes
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT
</code>
</a>
statements that do not
have an
<code class="literal">
INTO
<em class="replaceable">
<code>
var_list
</code>
</em>
</code>
clause and
other statements such as
<a class="link" href="show.html" title="15.7.7 SHOW Statements">
<code class="literal">
SHOW
</code>
</a>
,
<a class="link" href="explain.html" title="15.8.2 EXPLAIN Statement">
<code class="literal">
EXPLAIN
</code>
</a>
, and
<a class="link" href="check-table.html" title="15.7.3.2 CHECK TABLE Statement">
<code class="literal">
CHECK TABLE
</code>
</a>
. A function can
process a result set either with
<a class="link" href="select-into.html" title="15.2.13.1 SELECT ... INTO Statement">
<code class="literal">
SELECT ... INTO
<em class="replaceable">
<code>
var_list
</code>
</em>
</code>
</a>
or by using a
cursor and
<a class="link" href="fetch.html" title="15.6.6.3 Cursor FETCH Statement">
<code class="literal">
FETCH
</code>
</a>
statements.
See
<a class="xref" href="select-into.html" title="15.2.13.1 SELECT ... INTO Statement">
Section 15.2.13.1, “SELECT ... INTO Statement”
</a>
, and
<a class="xref" href="cursors.html" title="15.6.6 Cursors">
Section 15.6.6, “Cursors”
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a class="link" href="flush.html" title="15.7.8.3 FLUSH Statement">
<code class="literal">
FLUSH
</code>
</a>
statements.
</p>
</li>
<li class="listitem">
<p>
Stored functions cannot be used recursively.
</p>
</li>
<li class="listitem">
<p>
A stored function or trigger cannot modify a table that is
already being used (for reading or writing) by the statement
that invoked the function or trigger.
</p>
</li>
<li class="listitem">
<p>
If you refer to a temporary table multiple times in a stored
function under different aliases, a
<code class="literal">
Can't reopen
table:
'
<em class="replaceable">
<code>
tbl_name
</code>
</em>
<code class="literal">
</code>
'
</code>
error occurs, even if the references occur in different
statements within the function.
</p>
</li>
<li class="listitem">
<p>
<a class="link" href="handler.html" title="15.2.5 HANDLER Statement">
<code class="literal">
HANDLER ...
READ
</code>
</a>
statements that invoke stored functions can
cause replication errors and are disallowed.
</p>
</li>
</ul>
</div>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h3 class="title">
<a name="stored-routines-trigger-restrictions">
</a>
Restrictions for Triggers
</h3>
</div>
</div>
</div>
<p>
For triggers, the following additional restrictions apply:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
Triggers are not activated by foreign key actions.
</p>
</li>
<li class="listitem">
<p>
When using row-based replication, triggers on the replica
are not activated by statements originating on the source.
The triggers on the replica are activated when using
statement-based replication. For more information, see
<a class="xref" href="replication-features-triggers.html" title="19.5.1.36 Replication and Triggers">
Section 19.5.1.36, “Replication and Triggers”
</a>
.
</p>
</li>
<li class="listitem">
<p>
The
<a class="link" href="return.html" title="15.6.5.7 RETURN Statement">
<code class="literal">
RETURN
</code>
</a>
statement is not
permitted in triggers, which cannot return a value. To exit
a trigger immediately, use the
<a class="link" href="leave.html" title="15.6.5.4 LEAVE Statement">
<code class="literal">
LEAVE
</code>
</a>
statement.
</p>
</li>
<li class="listitem">
<p>
Triggers are not permitted on tables in the
<code class="literal">
mysql
</code>
database. Nor are they permitted on
<code class="literal">
INFORMATION_SCHEMA
</code>
or
<code class="literal">
performance_schema
</code>
tables. Those tables
are actually views and triggers are not permitted on views.
</p>
</li>
<li class="listitem">
<p>
The trigger cache does not detect when metadata of the
underlying objects has changed. If a trigger uses a table
and the table has changed since the trigger was loaded into
the cache, the trigger operates using the outdated metadata.
</p>
</li>
</ul>
</div>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h3 class="title">
<a name="stored-routine-name-conflicts">
</a>
Name Conflicts within Stored Routines
</h3>
</div>
</div>
</div>
<p>
The same identifier might be used for a routine parameter, a
local variable, and a table column. Also, the same local
variable name can be used in nested blocks. For example:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa54420625"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">PROCEDURE</span> p <span class="token punctuation">(</span>i <span class="token datatype">INT</span><span class="token punctuation">)</span>
<span class="token keyword">BEGIN</span>
<span class="token keyword">DECLARE</span> i <span class="token datatype">INT</span> <span class="token keyword">DEFAULT</span> <span class="token number">0</span><span class="token punctuation">;</span>
<span class="token keyword">SELECT</span> i <span class="token keyword">FROM</span> t<span class="token punctuation">;</span>
<span class="token keyword">BEGIN</span>
<span class="token keyword">DECLARE</span> i <span class="token datatype">INT</span> <span class="token keyword">DEFAULT</span> <span class="token number">1</span><span class="token punctuation">;</span>
<span class="token keyword">SELECT</span> i <span class="token keyword">FROM</span> t<span class="token punctuation">;</span>
<span class="token keyword">END</span><span class="token punctuation">;</span>
<span class="token keyword">END</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
In such cases, the identifier is ambiguous and the following
precedence rules apply:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
A local variable takes precedence over a routine parameter
or table column.
</p>
</li>
<li class="listitem">
<p>
A routine parameter takes precedence over a table column.
</p>
</li>
<li class="listitem">
<p>
A local variable in an inner block takes precedence over a
local variable in an outer block.
</p>
</li>
</ul>
</div>
<p>
The behavior that variables take precedence over table columns
is nonstandard.
</p>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h3 class="title">
<a name="stored-routines-replication-restrictions">
</a>
Replication Considerations
</h3>
</div>
</div>
</div>
<p>
Use of stored routines can cause replication problems. This
issue is discussed further in
<a class="xref" href="stored-programs-logging.html" title="27.7 Stored Program Binary Logging">
Section 27.7, “Stored Program Binary Logging”
</a>
.
</p>
<p>
The
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-wild-do-table">
<code class="option">
--replicate-wild-do-table=
<em class="replaceable">
<code>
db_name.tbl_name
</code>
</em>
</code>
</a>
option applies to tables, views, and triggers. It does not apply
to stored procedures and functions, or events. To filter
statements operating on the latter objects, use one or more of
the
<code class="option">
--replicate-*-db
</code>
options.
</p>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h3 class="title">
<a name="stored-routines-debugging-restrictions">
</a>
Debugging Considerations
</h3>
</div>
</div>
</div>
<p>
There are no stored routine debugging facilities.
</p>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h3 class="title">
<a name="stored-routines-standard-restrictions">
</a>
Unsupported Syntax from the SQL:2003 Standard
</h3>
</div>
</div>
</div>
<p>
The MySQL stored routine syntax is based on the SQL:2003
standard. The following items from that standard are not
currently supported:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<code class="literal">
UNDO
</code>
handlers
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
FOR
</code>
loops
</p>
</li>
</ul>
</div>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h3 class="title">
<a name="stored-routines-concurrency-restrictions">
</a>
Stored Routine Concurrency Considerations
</h3>
</div>
</div>
</div>
<p>
To prevent problems of interaction between sessions, when a
client issues a statement, the server uses a snapshot of
routines and triggers available for execution of the statement.
That is, the server calculates a list of procedures, functions,
and triggers that may be used during execution of the statement,
loads them, and then proceeds to execute the statement. While
the statement executes, it does not see changes to routines
performed by other sessions.
</p>
<p>
For maximum concurrency, stored functions should minimize their
side-effects; in particular, updating a table within a stored
function can reduce concurrent operations on that table. A
stored function acquires table locks before executing, to avoid
inconsistency in the binary log due to mismatch of the order in
which statements execute and when they appear in the log. When
statement-based binary logging is used, statements that invoke a
function are recorded rather than the statements executed within
the function. Consequently, stored functions that update the
same underlying tables do not execute in parallel. In contrast,
stored procedures do not acquire table-level locks. All
statements executed within stored procedures are written to the
binary log, even for statement-based binary logging. See
<a class="xref" href="stored-programs-logging.html" title="27.7 Stored Program Binary Logging">
Section 27.7, “Stored Program Binary Logging”
</a>
.
</p>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h3 class="title">
<a name="stored-routines-event-restrictions">
</a>
Event Scheduler Restrictions
</h3>
</div>
</div>
</div>
<p>
The following limitations are specific to the Event Scheduler:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
Event names are handled in case-insensitive fashion. For
example, you cannot have two events in the same database
with the names
<code class="literal">
anEvent
</code>
and
<code class="literal">
AnEvent
</code>
.
</p>
</li>
<li class="listitem">
<p>
An event may not be created from within a stored program. An
event may not be altered, or dropped from within a stored
program, if the event name is specified by means of a
variable. An event also may not create, alter, or drop
stored routines or triggers.
</p>
</li>
<li class="listitem">
<p>
DDL statements on events are prohibited while a
<a class="link" href="lock-tables.html" title="15.3.6 LOCK TABLES and UNLOCK TABLES Statements">
<code class="literal">
LOCK TABLES
</code>
</a>
statement is in
effect.
</p>
</li>
<li class="listitem">
<p>
Event timings using the intervals
<code class="literal">
YEAR
</code>
,
<code class="literal">
QUARTER
</code>
,
<code class="literal">
MONTH
</code>
, and
<code class="literal">
YEAR_MONTH
</code>
are resolved in months; those
using any other interval are resolved in seconds. There is
no way to cause events scheduled to occur at the same second
to execute in a given order. In addition—due to
rounding, the nature of threaded applications, and the fact
that a nonzero length of time is required to create events
and to signal their execution—events may be delayed by
as much as 1 or 2 seconds. However, the time shown in the
Information Schema
<a class="link" href="information-schema-events-table.html" title="28.3.14 The INFORMATION_SCHEMA EVENTS Table">
<code class="literal">
EVENTS
</code>
</a>
table's
<code class="literal">
LAST_EXECUTED
</code>
column is
always accurate to within one second of the actual event
execution time. (See also Bug #16522.)
</p>
</li>
<li class="listitem">
<p>
Each execution of the statements contained in the body of an
event takes place in a new connection; thus, these
statements have no effect in a given user session on the
server's statement counts such as
<code class="literal">
Com_select
</code>
and
<code class="literal">
Com_insert
</code>
that are displayed by
<a class="link" href="show-status.html" title="15.7.7.37 SHOW STATUS Statement">
<code class="literal">
SHOW STATUS
</code>
</a>
. However, such
counts
<span class="emphasis">
<em>
are
</em>
</span>
updated in the global scope.
(Bug #16422)
</p>
</li>
<li class="listitem">
<p>
Events do not support times later than the end of the Unix
Epoch; this is approximately the beginning of the year 2038.
Such dates are specifically not permitted by the Event
Scheduler. (Bug #16396)
</p>
</li>
<li class="listitem">
<p>
References to stored functions, loadable functions, and
tables in the
<code class="literal">
ON SCHEDULE
</code>
clauses of
<a class="link" href="create-event.html" title="15.1.13 CREATE EVENT Statement">
<code class="literal">
CREATE EVENT
</code>
</a>
and
<a class="link" href="alter-event.html" title="15.1.3 ALTER EVENT Statement">
<code class="literal">
ALTER EVENT
</code>
</a>
statements are
not supported. These sorts of references are not permitted.
(See Bug #22830 for more information.)
</p>
</li>
</ul>
</div>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h3 class="title">
<a name="stored-routines-ndbcluster">
</a>
Stored routines and triggers in NDB Cluster
</h3>
</div>
</div>
</div>
<p>
While stored procedures, stored functions, triggers, and
scheduled events are all supported by tables using the
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDB
</code>
</a>
storage engine, you must keep
in mind that these do
<span class="emphasis">
<em>
not
</em>
</span>
propagate
automatically between MySQL Servers acting as Cluster SQL nodes.
This is because stored routine and trigger definitions are
stored in tables in the
<code class="literal">
mysql
</code>
system database
using
<code class="literal">
InnoDB
</code>
tables, which are not copied
between Cluster nodes.
</p>
<p>
Any stored routine or trigger that interacts with MySQL Cluster
tables must be re-created by running the appropriate
<a class="link" href="create-procedure.html" title="15.1.17 CREATE PROCEDURE and CREATE FUNCTION Statements">
<code class="literal">
CREATE PROCEDURE
</code>
</a>
,
<a class="link" href="create-function.html" title="15.1.14 CREATE FUNCTION Statement">
<code class="literal">
CREATE FUNCTION
</code>
</a>
, or
<a class="link" href="create-trigger.html" title="15.1.22 CREATE TRIGGER Statement">
<code class="literal">
CREATE TRIGGER
</code>
</a>
statements on each
MySQL Server that participates in the cluster where you wish to
use the stored routine or trigger. Similarly, any changes to
existing stored routines or triggers must be carried out
explicitly on all Cluster SQL nodes, using the appropriate
<code class="literal">
ALTER
</code>
or
<code class="literal">
DROP
</code>
statements
on each MySQL Server accessing the cluster.
</p>
<div class="warning" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Warning
</div>
<p>
Do
<span class="emphasis">
<em>
not
</em>
</span>
attempt to work around the issue
just described by converting any
<code class="literal">
mysql
</code>
database tables to use the
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDB
</code>
</a>
storage engine.
<span class="emphasis">
<em>
Altering the system tables in the
<code class="literal">
mysql
</code>
database is not supported
</em>
</span>
and is very likely to produce undesirable results.
</p>
</div>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/point-in-time-recovery-binlog.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="point-in-time-recovery-binlog">
</a>
9.5.1 Point-in-Time Recovery Using Binary Log
</h3>
</div>
</div>
</div>
<p>
This section explains the general idea of using the binary log
to perform a point-in-time-recovery. The next section,
<a class="xref" href="point-in-time-recovery-positions.html" title="9.5.2 Point-in-Time Recovery Using Event Positions">
Section 9.5.2, “Point-in-Time Recovery Using Event Positions”
</a>
, explains the
operation in details with an example.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
Many of the examples in this and the next section use the
<a class="link" href="mysql.html" title="6.5.1 mysql — The MySQL Command-Line Client">
<span class="command">
<strong>
mysql
</strong>
</span>
</a>
client to process binary log output
produced by
<a class="link" href="mysqlbinlog.html" title="6.6.9 mysqlbinlog — Utility for Processing Binary Log Files">
<span class="command">
<strong>
mysqlbinlog
</strong>
</span>
</a>
. If your binary log
contains
<code class="literal">
\0
</code>
(null) characters, that output
cannot be parsed by
<a class="link" href="mysql.html" title="6.5.1 mysql — The MySQL Command-Line Client">
<span class="command">
<strong>
mysql
</strong>
</span>
</a>
unless you invoke
it with the
<a class="link" href="mysql-command-options.html#option_mysql_binary-mode">
<code class="option">
--binary-mode
</code>
</a>
option.
</p>
</div>
<p>
The source of information for point-in-time recovery is the set
of binary log files generated subsequent to the full backup
operation. Therefore, to allow a server to be restored to a
point-in-time, binary logging must be enabled on it, which is
the default setting for MySQL 8.4
(see
<a class="xref" href="binary-log.html" title="7.4.4 The Binary Log">
Section 7.4.4, “The Binary Log”
</a>
).
</p>
<p>
To restore data from the binary log, you must know the name and
location of the current binary log files. By default, the server
creates binary log files in the data directory, but a path name
can be specified with the
<a class="link" href="replication-options-binary-log.html#option_mysqld_log-bin">
<code class="option">
--log-bin
</code>
</a>
option to place the
files in a different location. To see a listing of all binary
log files, use this statement:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa82463346"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SHOW</span> <span class="token datatype">BINARY</span> <span class="token keyword">LOGS</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
To determine the name of the current binary log file, issue the
following statement:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa79937189"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SHOW</span> <span class="token datatype">BINARY</span> LOG <span class="token keyword">STATUS</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
The
<a class="link" href="mysqlbinlog.html" title="6.6.9 mysqlbinlog — Utility for Processing Binary Log Files">
<span class="command">
<strong>
mysqlbinlog
</strong>
</span>
</a>
utility converts the events
in the binary log files from binary format to text so that they
can be viewed or applied.
<a class="link" href="mysqlbinlog.html" title="6.6.9 mysqlbinlog — Utility for Processing Binary Log Files">
<span class="command">
<strong>
mysqlbinlog
</strong>
</span>
</a>
has
options for selecting sections of the binary log based on event
times or position of events within the log. See
<a class="xref" href="mysqlbinlog.html" title="6.6.9 mysqlbinlog — Utility for Processing Binary Log Files">
Section 6.6.9, “mysqlbinlog — Utility for Processing Binary Log Files”
</a>
.
</p>
<p>
Applying events from the binary log causes the data
modifications they represent to be reexecuted. This enables
recovery of data changes for a given span of time. To apply
events from the binary log, process
<a class="link" href="mysqlbinlog.html" title="6.6.9 mysqlbinlog — Utility for Processing Binary Log Files">
<span class="command">
<strong>
mysqlbinlog
</strong>
</span>
</a>
output using the
<a class="link" href="mysql.html" title="6.5.1 mysql — The MySQL Command-Line Client">
<span class="command">
<strong>
mysql
</strong>
</span>
</a>
client:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-terminal"><div class="docs-select-all right" id="sa5857827"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-terminal"><span class="token prompt">$> </span><span class="token command">mysqlbinlog</span> <em class="replaceable">binlog_files</em> | mysql <span class="token property">-u</span> root <span class="token property">-p</span></code></pre>
</div>
<p>
If binary log files have been encrypted,
<a class="link" href="mysqlbinlog.html" title="6.6.9 mysqlbinlog — Utility for Processing Binary Log Files">
<span class="command">
<strong>
mysqlbinlog
</strong>
</span>
</a>
cannot read them directly as in
the previous example, but can read them from the server using
the
<a class="link" href="mysqlbinlog.html#option_mysqlbinlog_read-from-remote-server">
<code class="option">
--read-from-remote-server
</code>
</a>
(
<code class="literal">
-R
</code>
) option. For example:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-terminal"><div class="docs-select-all right" id="sa56632642"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-terminal"><span class="token prompt">$> </span><span class="token command">mysqlbinlog</span> <span class="token property">--read-from-remote-server</span> <span class="token constant">--host</span><span class="token attr-value"><span class="token punctuation">=</span><em class="replaceable">host_name</em></span> <span class="token constant">--port</span><span class="token attr-value"><span class="token punctuation">=</span>3306</span> <span class="token constant">--user</span><span class="token attr-value"><span class="token punctuation">=</span>root</span> <span class="token property">--password</span> <span class="token constant">--ssl-mode</span><span class="token attr-value"><span class="token punctuation">=</span>required</span> <em class="replaceable">binlog_files</em> | mysql <span class="token property">-u</span> root <span class="token property">-p</span></code></pre>
</div>
<p>
Here, the option
<code class="option">
--ssl-mode=required
</code>
has been
used to ensure that the data from the binary log files is
protected in transit, because it is sent to
<a class="link" href="mysqlbinlog.html" title="6.6.9 mysqlbinlog — Utility for Processing Binary Log Files">
<span class="command">
<strong>
mysqlbinlog
</strong>
</span>
</a>
in an unencrypted format.
</p>
<div class="important" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Important
</div>
<p>
<code class="literal">
VERIFY_CA
</code>
and
<code class="literal">
VERIFY_IDENTITY
</code>
are better choices than
<code class="literal">
REQUIRED
</code>
for the SSL mode, because they
help prevent man-in-the-middle attacks. To implement one of
these settings, you must first ensure that the CA certificate
for the server is reliably available to all the clients that
use it in your environment, otherwise availability issues will
result. See
<a class="xref" href="connection-options.html#encrypted-connection-options" title="Command Options for Encrypted Connections">
Command Options for Encrypted Connections
</a>
.
</p>
</div>
<p>
Viewing log contents can be useful when you need to determine
event times or positions to select partial log contents prior to
executing events. To view events from the log, send
<a class="link" href="mysqlbinlog.html" title="6.6.9 mysqlbinlog — Utility for Processing Binary Log Files">
<span class="command">
<strong>
mysqlbinlog
</strong>
</span>
</a>
output into a paging program:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-terminal"><div class="docs-select-all right" id="sa77113729"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-terminal"><span class="token prompt">$> </span><span class="token command">mysqlbinlog</span> <em class="replaceable">binlog_files</em> | more</code></pre>
</div>
<p>
Alternatively, save the output in a file and view the file in a
text editor:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-terminal"><div class="docs-select-all right" id="sa28287031"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-terminal"><span class="token prompt">$> </span><span class="token command">mysqlbinlog</span> <em class="replaceable">binlog_files</em> > tmpfile
<span class="token prompt">$> </span><span class="token command">...</span> <em class="replaceable">edit tmpfile</em> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span></code></pre>
</div>
<p>
After editing the file, apply the contents as follows:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-terminal"><div class="docs-select-all right" id="sa71499053"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-terminal"><span class="token prompt">$> </span><span class="token command">mysql</span> <span class="token property">-u</span> root <span class="token property">-p</span> < tmpfile</code></pre>
</div>
<p>
If you have more than one binary log to apply on the MySQL
server, use a single connection to apply the contents of all
binary log files that you want to process. Here is one way to do
so:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-terminal"><div class="docs-select-all right" id="sa83379557"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-terminal"><span class="token prompt">$> </span><span class="token command">mysqlbinlog</span> binlog<span class="token punctuation">.</span>000001 binlog<span class="token punctuation">.</span>000002 | mysql <span class="token property">-u</span> root <span class="token property">-p</span></code></pre>
</div>
<p>
Another approach is to write the whole log to a single file and
then process the file:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-terminal"><div class="docs-select-all right" id="sa3317886"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-terminal"><span class="token prompt">$> </span><span class="token command">mysqlbinlog</span> binlog<span class="token punctuation">.</span>000001 > /tmp/statements<span class="token punctuation">.</span>sql
<span class="token prompt">$> </span><span class="token command">mysqlbinlog</span> binlog<span class="token punctuation">.</span>000002 >> /tmp/statements<span class="token punctuation">.</span>sql
<span class="token prompt">$> </span><span class="token command">mysql</span> <span class="token property">-u</span> root <span class="token property">-p</span> <span class="token property">-e</span> <span class="token atrule">"source /tmp/statements.sql"</span></code></pre>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/data-dictionary-transactional-storage.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h2 class="title">
<a name="data-dictionary-transactional-storage">
</a>
16.3 Transactional Storage of Dictionary Data
</h2>
</div>
</div>
</div>
<a class="indexterm" name="idm46045167742880">
</a>
<p>
The data dictionary schema stores dictionary data in transactional
(
<code class="literal">
InnoDB
</code>
) tables. Data dictionary tables are
located in the
<code class="filename">
mysql
</code>
database together with
non-data dictionary system tables.
</p>
<p>
Data dictionary tables are created in a single
<code class="literal">
InnoDB
</code>
tablespace named
<code class="filename">
mysql.ibd
</code>
, which resides in the MySQL data
directory. The
<code class="filename">
mysql.ibd
</code>
tablespace file must
reside in the MySQL data directory and its name cannot be modified
or used by another tablespace.
</p>
<p>
Dictionary data is protected by the same commit, rollback, and
crash-recovery capabilities that protect user data that is stored
in
<code class="literal">
InnoDB
</code>
tables.
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/replication-options-replica.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="replication-options-replica">
</a>
19.1.6.3 Replica Server Options and Variables
</h4>
</div>
</div>
</div>
<p>
This section explains the server options and system variables that
apply to replica servers and contains the following:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<a class="xref" href="replication-options-replica.html#replication-optvars-slaves" title="Startup Options for Replica Servers">
Startup Options for Replica Servers
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="replication-options-replica.html#replication-sysvars-slaves" title="System Variables Used on Replica Servers">
System Variables Used on Replica Servers
</a>
</p>
</li>
</ul>
</div>
<p>
Specify the options either on the
<a class="link" href="command-line-options.html" title="6.2.2.1 Using Options on the Command Line">
command line
</a>
or in an
<a class="link" href="option-files.html" title="6.2.2.2 Using Option Files">
option file
</a>
. Many of the
options can be set while the server is running by using the
<a class="link" href="change-replication-source-to.html" title="15.4.2.2 CHANGE REPLICATION SOURCE TO Statement">
<code class="literal">
CHANGE REPLICATION SOURCE TO
</code>
</a>
statement. Specify system variable values using
<a class="link" href="set-variable.html" title="15.7.6.1 SET Syntax for Variable Assignment">
<code class="literal">
SET
</code>
</a>
.
</p>
<p>
<b>
Server ID.
</b>
On the source and each replica, you must set the
<a class="link" href="replication-options.html#sysvar_server_id">
<code class="literal">
server_id
</code>
</a>
system variable to
establish a unique replication ID in the range from 1 to
2
<sup>
32
</sup>
− 1.
<span class="quote">
“
<span class="quote">
Unique
</span>
”
</span>
means that each ID must be different from every other ID in use
by any other source or replica in the replication topology.
Example
<code class="filename">
my.cnf
</code>
file:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-ini"><div class="docs-select-all right" id="sa27801978"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-ini"><span class="token selector">[mysqld]</span>
<span class="token constant">server-id</span><span class="token attr-value"><span class="token punctuation">=</span>3</span></code></pre>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h5 class="title">
<a name="replication-optvars-slaves">
</a>
Startup Options for Replica Servers
</h5>
</div>
</div>
</div>
<p>
This section explains startup options for controlling replica
servers. Many of these options can be set while the server is
running by using the
<a class="link" href="change-replication-source-to.html" title="15.4.2.2 CHANGE REPLICATION SOURCE TO Statement">
<code class="literal">
CHANGE REPLICATION
SOURCE TO
</code>
</a>
statement. Others, such as the
<code class="option">
--replicate-*
</code>
options, can be set only when the
replica server starts. Replication-related system variables are
discussed later in this section.
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<a name="option_mysqld_master-retry-count">
</a>
<a class="link" href="replication-options-replica.html#option_mysqld_master-retry-count">
<code class="option">
--master-retry-count=
<em class="replaceable">
<code>
count
</code>
</em>
</code>
</a>
</p>
<a class="indexterm" name="idm46045143879712">
</a>
<a class="indexterm" name="idm46045143878256">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for master-retry-count">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--master-retry-count=#
</code>
</td>
</tr>
<tr>
<th>
Deprecated
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Integer
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
10
</code>
</td>
</tr>
<tr>
<th>
Minimum Value
</th>
<td>
<code class="literal">
0
</code>
</td>
</tr>
<tr>
<th>
Maximum Value (64-bit platforms)
</th>
<td>
<code class="literal">
18446744073709551615
</code>
</td>
</tr>
<tr>
<th>
Maximum Value (32-bit platforms)
</th>
<td>
<code class="literal">
4294967295
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
This option is deprecated; expect it to be removed in a
future MySQL release. Use the
<code class="literal">
SOURCE_RETRY_COUNT
</code>
option of the
<a class="link" href="change-replication-source-to.html" title="15.4.2.2 CHANGE REPLICATION SOURCE TO Statement">
<code class="literal">
CHANGE REPLICATION SOURCE TO
</code>
</a>
statement, instead.
</p>
</li>
<li class="listitem">
<p>
<a name="option_mysqld_max-relay-log-size">
</a>
<a class="link" href="replication-options-replica.html#option_mysqld_max-relay-log-size">
<code class="option">
--max-relay-log-size=
<em class="replaceable">
<code>
size
</code>
</em>
</code>
</a>
</p>
<a class="indexterm" name="idm46045143852192">
</a>
<a class="indexterm" name="idm46045143850736">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for max_relay_log_size">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--max-relay-log-size=#
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_max_relay_log_size">
max_relay_log_size
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Integer
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
0
</code>
</td>
</tr>
<tr>
<th>
Minimum Value
</th>
<td>
<code class="literal">
0
</code>
</td>
</tr>
<tr>
<th>
Maximum Value
</th>
<td>
<code class="literal">
1073741824
</code>
</td>
</tr>
<tr>
<th>
Unit
</th>
<td>
bytes
</td>
</tr>
<tr>
<th>
<a class="link" href="server-system-variables.html#system-variables-block-size" title="Note">
Block Size
</a>
</th>
<td>
<code class="literal">
4096
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
The size at which the server rotates relay log files
automatically. If this value is nonzero, the relay log is
rotated automatically when its size exceeds this value. If
this value is zero (the default), the size at which relay
log rotation occurs is determined by the value of
<a class="link" href="replication-options-binary-log.html#sysvar_max_binlog_size">
<code class="literal">
max_binlog_size
</code>
</a>
. For more
information, see
<a class="xref" href="replica-logs-relaylog.html" title="19.2.4.1 The Relay Log">
Section 19.2.4.1, “The Relay Log”
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a name="option_mysqld_relay-log-purge">
</a>
<a class="link" href="replication-options-replica.html#option_mysqld_relay-log-purge">
<code class="option">
--relay-log-purge={0|1}
</code>
</a>
</p>
<a class="indexterm" name="idm46045143814160">
</a>
<a class="indexterm" name="idm46045143812672">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for relay_log_purge">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--relay-log-purge[={OFF|ON}]
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_relay_log_purge">
relay_log_purge
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Boolean
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
ON
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
Disable or enable automatic purging of relay logs as soon as
they are no longer needed. The default value is 1 (enabled).
This is a global variable that can be changed dynamically
with
<code class="literal">
SET GLOBAL relay_log_purge =
<em class="replaceable">
<code>
N
</code>
</em>
</code>
. Disabling purging of
relay logs when enabling the
<a class="link" href="replication-options-replica.html#sysvar_relay_log_recovery">
<code class="option">
--relay-log-recovery
</code>
</a>
option
risks data consistency and is therefore not crash-safe.
</p>
</li>
<li class="listitem">
<p>
<a name="option_mysqld_relay-log-space-limit">
</a>
<a class="link" href="replication-options-replica.html#option_mysqld_relay-log-space-limit">
<code class="option">
--relay-log-space-limit=
<em class="replaceable">
<code>
size
</code>
</em>
</code>
</a>
</p>
<a class="indexterm" name="idm46045143785744">
</a>
<a class="indexterm" name="idm46045143784240">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for relay_log_space_limit">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--relay-log-space-limit=#
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_relay_log_space_limit">
relay_log_space_limit
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
No
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Integer
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
0
</code>
</td>
</tr>
<tr>
<th>
Minimum Value
</th>
<td>
<code class="literal">
0
</code>
</td>
</tr>
<tr>
<th>
Maximum Value
</th>
<td>
<code class="literal">
18446744073709551615
</code>
</td>
</tr>
<tr>
<th>
Unit
</th>
<td>
bytes
</td>
</tr>
</tbody>
</table>
</div>
<p>
This option places an upper limit on the total size in bytes
of all relay logs on the replica. A value of 0 means
<span class="quote">
“
<span class="quote">
no limit
</span>
”
</span>
. This is useful for a replica server
host that has limited disk space. When the limit is reached,
the I/O (receiver) thread stops reading binary log events
from the source server until the SQL thread has caught up
and deleted some unused relay logs. Note that this limit is
not absolute: There are cases where the SQL (applier) thread
needs more events before it can delete relay logs. In that
case, the receiver thread exceeds the limit until it becomes
possible for the applier thread to delete some relay logs
because not doing so would cause a deadlock. You should not
set
<a class="link" href="replication-options-replica.html#option_mysqld_relay-log-space-limit">
<code class="option">
--relay-log-space-limit
</code>
</a>
to less than twice the value of
<a class="link" href="replication-options-replica.html#option_mysqld_max-relay-log-size">
<code class="option">
--max-relay-log-size
</code>
</a>
(or
<a class="link" href="replication-options-binary-log.html#sysvar_max_binlog_size">
<code class="option">
--max-binlog-size
</code>
</a>
if
<a class="link" href="replication-options-replica.html#option_mysqld_max-relay-log-size">
<code class="option">
--max-relay-log-size
</code>
</a>
is 0).
In that case, there is a chance that the receiver thread
waits for free space because
<a class="link" href="replication-options-replica.html#option_mysqld_relay-log-space-limit">
<code class="option">
--relay-log-space-limit
</code>
</a>
is
exceeded, but the applier thread has no relay log to purge
and is unable to satisfy the receiver thread. This forces
the receiver thread to ignore
<a class="link" href="replication-options-replica.html#option_mysqld_relay-log-space-limit">
<code class="option">
--relay-log-space-limit
</code>
</a>
temporarily.
</p>
</li>
<li class="listitem">
<p>
<a name="option_mysqld_replicate-do-db">
</a>
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-do-db">
<code class="option">
--replicate-do-db=
<em class="replaceable">
<code>
db_name
</code>
</em>
</code>
</a>
</p>
<a class="indexterm" name="idm46045143745984">
</a>
<a class="indexterm" name="idm46045143744496">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for replicate-do-db">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--replicate-do-db=name
</code>
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
String
</td>
</tr>
</tbody>
</table>
</div>
<p>
Creates a replication filter using the name of a database.
Such filters can also be created using
<a class="link" href="change-replication-filter.html" title="15.4.2.1 CHANGE REPLICATION FILTER Statement">
<code class="literal">
CHANGE
REPLICATION FILTER REPLICATE_DO_DB
</code>
</a>
.
</p>
<p>
This option supports channel specific replication filters,
enabling multi-source replicas to use specific filters for
different sources. To configure a channel specific
replication filter on a channel named
<em class="replaceable">
<code>
channel_1
</code>
</em>
use
<code class="option">
--replicate-do-db:
<em class="replaceable">
<code>
channel_1
</code>
</em>
:
<em class="replaceable">
<code>
db_name
</code>
</em>
</code>
.
In this case, the first colon is interpreted as a separator
and subsequent colons are literal colons. See
<a class="xref" href="replication-rules-channel-based-filters.html" title="19.2.5.4 Replication Channel Based Filters">
Section 19.2.5.4, “Replication Channel Based Filters”
</a>
for more information.
</p>
<p>
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
Global replication filters cannot be used on a MySQL
server instance that is configured for Group
Replication, because filtering transactions on some
servers would make the group unable to reach agreement
on a consistent state. Channel specific replication
filters can be used on replication channels that are not
directly involved with Group Replication, such as where
a group member also acts as a replica to a source that
is outside the group. They cannot be used on the
<code class="literal">
group_replication_applier
</code>
or
<code class="literal">
group_replication_recovery
</code>
channels.
</p>
</div>
<p>
</p>
<p>
The precise effect of this replication filter depends on
whether statement-based or row-based replication is in use.
</p>
<p>
<b>
Statement-based replication.
</b>
Tell the replication SQL thread to restrict replication to
statements where the default database (that is, the one
selected by
<a class="link" href="use.html" title="15.8.4 USE Statement">
<code class="literal">
USE
</code>
</a>
) is
<em class="replaceable">
<code>
db_name
</code>
</em>
. To specify more than
one database, use this option multiple times, once for
each database; however, doing so does
<span class="emphasis">
<em>
not
</em>
</span>
replicate cross-database
statements such as
<code class="literal">
UPDATE
<em class="replaceable">
<code>
some_db.some_table
</code>
</em>
SET
foo='bar'
</code>
while a different database (or no
database) is selected.
</p>
<div class="warning" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Warning
</div>
<p>
To specify multiple databases you
<span class="emphasis">
<em>
must
</em>
</span>
use multiple instances of this
option. Because database names can contain commas, if you
supply a comma separated list then the list is treated as
the name of a single database.
</p>
</div>
<p>
An example of what does not work as you might expect when
using statement-based replication: If the replica is started
with
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-do-db">
<code class="option">
--replicate-do-db=sales
</code>
</a>
and you issue the following statements on the source, the
<a class="link" href="update.html" title="15.2.17 UPDATE Statement">
<code class="literal">
UPDATE
</code>
</a>
statement is
<span class="emphasis">
<em>
not
</em>
</span>
replicated:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa61287649"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">USE</span> prices<span class="token punctuation">;</span>
<span class="token keyword">UPDATE</span> sales<span class="token punctuation">.</span>january <span class="token keyword">SET</span> amount<span class="token operator">=</span>amount<span class="token operator">+</span><span class="token number">1000</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
The main reason for this
<span class="quote">
“
<span class="quote">
check just the default
database
</span>
”
</span>
behavior is that it is difficult from the
statement alone to know whether it should be replicated (for
example, if you are using multiple-table
<a class="link" href="delete.html" title="15.2.2 DELETE Statement">
<code class="literal">
DELETE
</code>
</a>
statements or
multiple-table
<a class="link" href="update.html" title="15.2.17 UPDATE Statement">
<code class="literal">
UPDATE
</code>
</a>
statements that act across multiple databases). It is also
faster to check only the default database rather than all
databases if there is no need.
</p>
<p>
<b>
Row-based replication.
</b>
Tells the replication SQL thread to restrict replication
to database
<em class="replaceable">
<code>
db_name
</code>
</em>
. Only
tables belonging to
<em class="replaceable">
<code>
db_name
</code>
</em>
are
changed; the current database has no effect on this.
Suppose that the replica is started with
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-do-db">
<code class="option">
--replicate-do-db=sales
</code>
</a>
and
row-based replication is in effect, and then the following
statements are run on the source:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa88155166"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">USE</span> prices<span class="token punctuation">;</span>
<span class="token keyword">UPDATE</span> sales<span class="token punctuation">.</span>february <span class="token keyword">SET</span> amount<span class="token operator">=</span>amount<span class="token operator">+</span><span class="token number">100</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
The
<code class="literal">
february
</code>
table in the
<code class="literal">
sales
</code>
database on the replica is changed
in accordance with the
<a class="link" href="update.html" title="15.2.17 UPDATE Statement">
<code class="literal">
UPDATE
</code>
</a>
statement; this occurs whether or not the
<a class="link" href="use.html" title="15.8.4 USE Statement">
<code class="literal">
USE
</code>
</a>
statement was issued.
However, issuing the following statements on the source has
no effect on the replica when using row-based replication
and
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-do-db">
<code class="option">
--replicate-do-db=sales
</code>
</a>
:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa78771600"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">USE</span> prices<span class="token punctuation">;</span>
<span class="token keyword">UPDATE</span> prices<span class="token punctuation">.</span>march <span class="token keyword">SET</span> amount<span class="token operator">=</span>amount<span class="token number">-25</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
Even if the statement
<code class="literal">
USE prices
</code>
were
changed to
<code class="literal">
USE sales
</code>
, the
<a class="link" href="update.html" title="15.2.17 UPDATE Statement">
<code class="literal">
UPDATE
</code>
</a>
statement's
effects would still not be replicated.
</p>
<p>
Another important difference in how
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-do-db">
<code class="option">
--replicate-do-db
</code>
</a>
is handled
in statement-based replication as opposed to row-based
replication occurs with regard to statements that refer to
multiple databases. Suppose that the replica is started with
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-do-db">
<code class="option">
--replicate-do-db=db1
</code>
</a>
, and
the following statements are executed on the source:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa16055143"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">USE</span> db1<span class="token punctuation">;</span>
<span class="token keyword">UPDATE</span> db1<span class="token punctuation">.</span>table1<span class="token punctuation">,</span> db2<span class="token punctuation">.</span>table2 <span class="token keyword">SET</span> db1<span class="token punctuation">.</span>table1<span class="token punctuation">.</span>col1 <span class="token operator">=</span> <span class="token number">10</span><span class="token punctuation">,</span> db2<span class="token punctuation">.</span>table2<span class="token punctuation">.</span>col2 <span class="token operator">=</span> <span class="token number">20</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
If you are using statement-based replication, then both
tables are updated on the replica. However, when using
row-based replication, only
<code class="literal">
table1
</code>
is
affected on the replica; since
<code class="literal">
table2
</code>
is
in a different database,
<code class="literal">
table2
</code>
on the
replica is not changed by the
<a class="link" href="update.html" title="15.2.17 UPDATE Statement">
<code class="literal">
UPDATE
</code>
</a>
. Now suppose that,
instead of the
<code class="literal">
USE db1
</code>
statement, a
<code class="literal">
USE db4
</code>
statement had been used:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa8995926"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">USE</span> db4<span class="token punctuation">;</span>
<span class="token keyword">UPDATE</span> db1<span class="token punctuation">.</span>table1<span class="token punctuation">,</span> db2<span class="token punctuation">.</span>table2 <span class="token keyword">SET</span> db1<span class="token punctuation">.</span>table1<span class="token punctuation">.</span>col1 <span class="token operator">=</span> <span class="token number">10</span><span class="token punctuation">,</span> db2<span class="token punctuation">.</span>table2<span class="token punctuation">.</span>col2 <span class="token operator">=</span> <span class="token number">20</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
In this case, the
<a class="link" href="update.html" title="15.2.17 UPDATE Statement">
<code class="literal">
UPDATE
</code>
</a>
statement would have no effect on the replica when using
statement-based replication. However, if you are using
row-based replication, the
<a class="link" href="update.html" title="15.2.17 UPDATE Statement">
<code class="literal">
UPDATE
</code>
</a>
would change
<code class="literal">
table1
</code>
on the replica, but not
<code class="literal">
table2
</code>
—in other words, only tables
in the database named by
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-do-db">
<code class="option">
--replicate-do-db
</code>
</a>
are
changed, and the choice of default database has no effect on
this behavior.
</p>
<p>
If you need cross-database updates to work, use
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-wild-do-table">
<code class="option">
--replicate-wild-do-table=
<em class="replaceable">
<code>
db_name
</code>
</em>
.%
</code>
</a>
instead. See
<a class="xref" href="replication-rules.html" title="19.2.5 How Servers Evaluate Replication Filtering Rules">
Section 19.2.5, “How Servers Evaluate Replication Filtering Rules”
</a>
.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
This option affects replication in the same manner that
<a class="link" href="replication-options-binary-log.html#option_mysqld_binlog-do-db">
<code class="option">
--binlog-do-db
</code>
</a>
affects
binary logging, and the effects of the replication format
on how
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-do-db">
<code class="option">
--replicate-do-db
</code>
</a>
affects replication behavior are the same as those of the
logging format on the behavior of
<a class="link" href="replication-options-binary-log.html#option_mysqld_binlog-do-db">
<code class="option">
--binlog-do-db
</code>
</a>
.
</p>
<p>
This option has no effect on
<a class="link" href="commit.html" title="15.3.1 START TRANSACTION, COMMIT, and ROLLBACK Statements">
<code class="literal">
BEGIN
</code>
</a>
,
<a class="link" href="commit.html" title="15.3.1 START TRANSACTION, COMMIT, and ROLLBACK Statements">
<code class="literal">
COMMIT
</code>
</a>
, or
<a class="link" href="commit.html" title="15.3.1 START TRANSACTION, COMMIT, and ROLLBACK Statements">
<code class="literal">
ROLLBACK
</code>
</a>
statements.
</p>
</div>
</li>
<li class="listitem">
<p>
<a name="option_mysqld_replicate-ignore-db">
</a>
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-ignore-db">
<code class="option">
--replicate-ignore-db=
<em class="replaceable">
<code>
db_name
</code>
</em>
</code>
</a>
</p>
<a class="indexterm" name="idm46045143668800">
</a>
<a class="indexterm" name="idm46045143667344">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for replicate-ignore-db">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--replicate-ignore-db=name
</code>
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
String
</td>
</tr>
</tbody>
</table>
</div>
<p>
Creates a replication filter using the name of a database.
Such filters can also be created using
<a class="link" href="change-replication-filter.html" title="15.4.2.1 CHANGE REPLICATION FILTER Statement">
<code class="literal">
CHANGE
REPLICATION FILTER REPLICATE_IGNORE_DB
</code>
</a>
.
</p>
<p>
This option supports channel specific replication filters,
enabling multi-source replicas to use specific filters for
different sources. To configure a channel specific
replication filter on a channel named
<em class="replaceable">
<code>
channel_1
</code>
</em>
use
<code class="option">
--replicate-ignore-db:
<em class="replaceable">
<code>
channel_1
</code>
</em>
:
<em class="replaceable">
<code>
db_name
</code>
</em>
</code>
.
In this case, the first colon is interpreted as a separator
and subsequent colons are literal colons. See
<a class="xref" href="replication-rules-channel-based-filters.html" title="19.2.5.4 Replication Channel Based Filters">
Section 19.2.5.4, “Replication Channel Based Filters”
</a>
for more information.
</p>
<p>
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
Global replication filters cannot be used on a MySQL
server instance that is configured for Group
Replication, because filtering transactions on some
servers would make the group unable to reach agreement
on a consistent state. Channel specific replication
filters can be used on replication channels that are not
directly involved with Group Replication, such as where
a group member also acts as a replica to a source that
is outside the group. They cannot be used on the
<code class="literal">
group_replication_applier
</code>
or
<code class="literal">
group_replication_recovery
</code>
channels.
</p>
</div>
<p>
</p>
<p>
To specify more than one database to ignore, use this option
multiple times, once for each database. Because database
names can contain commas, if you supply a comma-separated
list, it is treated as the name of a single database.
</p>
<p>
As with
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-do-db">
<code class="option">
--replicate-do-db
</code>
</a>
,
the precise effect of this filtering depends on whether
statement-based or row-based replication is in use, and are
described in the next several paragraphs.
</p>
<p>
<b>
Statement-based replication.
</b>
Tells the replication SQL thread not to replicate any
statement where the default database (that is, the one
selected by
<a class="link" href="use.html" title="15.8.4 USE Statement">
<code class="literal">
USE
</code>
</a>
) is
<em class="replaceable">
<code>
db_name
</code>
</em>
.
</p>
<p>
<b>
Row-based replication.
</b>
Tells the replication SQL thread not to update any tables
in the database
<em class="replaceable">
<code>
db_name
</code>
</em>
. The
default database has no effect.
</p>
<p>
When using statement-based replication, the following
example does not work as you might expect. Suppose that the
replica is started with
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-ignore-db">
<code class="option">
--replicate-ignore-db=sales
</code>
</a>
and you issue the following statements on the source:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa35882621"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">USE</span> prices<span class="token punctuation">;</span>
<span class="token keyword">UPDATE</span> sales<span class="token punctuation">.</span>january <span class="token keyword">SET</span> amount<span class="token operator">=</span>amount<span class="token operator">+</span><span class="token number">1000</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
The
<a class="link" href="update.html" title="15.2.17 UPDATE Statement">
<code class="literal">
UPDATE
</code>
</a>
statement
<span class="emphasis">
<em>
is
</em>
</span>
replicated in such a case because
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-ignore-db">
<code class="option">
--replicate-ignore-db
</code>
</a>
applies
only to the default database (determined by the
<a class="link" href="use.html" title="15.8.4 USE Statement">
<code class="literal">
USE
</code>
</a>
statement). Because the
<code class="literal">
sales
</code>
database was specified explicitly
in the statement, the statement has not been filtered.
However, when using row-based replication, the
<a class="link" href="update.html" title="15.2.17 UPDATE Statement">
<code class="literal">
UPDATE
</code>
</a>
statement's
effects are
<span class="emphasis">
<em>
not
</em>
</span>
propagated to the
replica, and the replica's copy of the
<code class="literal">
sales.january
</code>
table is unchanged; in this
instance,
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-ignore-db">
<code class="option">
--replicate-ignore-db=sales
</code>
</a>
causes
<span class="emphasis">
<em>
all
</em>
</span>
changes made to tables in
the source's copy of the
<code class="literal">
sales
</code>
database to be ignored by the replica.
</p>
<p>
You should not use this option if you are using
cross-database updates and you do not want these updates to
be replicated. See
<a class="xref" href="replication-rules.html" title="19.2.5 How Servers Evaluate Replication Filtering Rules">
Section 19.2.5, “How Servers Evaluate Replication Filtering Rules”
</a>
.
</p>
<p>
If you need cross-database updates to work, use
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-wild-ignore-table">
<code class="option">
--replicate-wild-ignore-table=
<em class="replaceable">
<code>
db_name
</code>
</em>
.%
</code>
</a>
instead. See
<a class="xref" href="replication-rules.html" title="19.2.5 How Servers Evaluate Replication Filtering Rules">
Section 19.2.5, “How Servers Evaluate Replication Filtering Rules”
</a>
.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
This option affects replication in the same manner that
<a class="link" href="replication-options-binary-log.html#option_mysqld_binlog-ignore-db">
<code class="option">
--binlog-ignore-db
</code>
</a>
affects
binary logging, and the effects of the replication format
on how
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-ignore-db">
<code class="option">
--replicate-ignore-db
</code>
</a>
affects replication behavior are the same as those of the
logging format on the behavior of
<a class="link" href="replication-options-binary-log.html#option_mysqld_binlog-ignore-db">
<code class="option">
--binlog-ignore-db
</code>
</a>
.
</p>
<p>
This option has no effect on
<a class="link" href="commit.html" title="15.3.1 START TRANSACTION, COMMIT, and ROLLBACK Statements">
<code class="literal">
BEGIN
</code>
</a>
,
<a class="link" href="commit.html" title="15.3.1 START TRANSACTION, COMMIT, and ROLLBACK Statements">
<code class="literal">
COMMIT
</code>
</a>
, or
<a class="link" href="commit.html" title="15.3.1 START TRANSACTION, COMMIT, and ROLLBACK Statements">
<code class="literal">
ROLLBACK
</code>
</a>
statements.
</p>
</div>
</li>
<li class="listitem">
<p>
<a name="option_mysqld_replicate-do-table">
</a>
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-do-table">
<code class="option">
--replicate-do-table=
<em class="replaceable">
<code>
db_name.tbl_name
</code>
</em>
</code>
</a>
</p>
<a class="indexterm" name="idm46045143615152">
</a>
<a class="indexterm" name="idm46045143613696">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for replicate-do-table">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--replicate-do-table=name
</code>
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
String
</td>
</tr>
</tbody>
</table>
</div>
<p>
Creates a replication filter by telling the replication SQL
thread to restrict replication to a given table. To specify
more than one table, use this option multiple times, once
for each table. This works for both cross-database updates
and default database updates, in contrast to
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-do-db">
<code class="option">
--replicate-do-db
</code>
</a>
. See
<a class="xref" href="replication-rules.html" title="19.2.5 How Servers Evaluate Replication Filtering Rules">
Section 19.2.5, “How Servers Evaluate Replication Filtering Rules”
</a>
. You can also create
such a filter by issuing a
<a class="link" href="change-replication-filter.html" title="15.4.2.1 CHANGE REPLICATION FILTER Statement">
<code class="literal">
CHANGE
REPLICATION FILTER REPLICATE_DO_TABLE
</code>
</a>
statement.
</p>
<p>
This option supports channel specific replication filters,
enabling multi-source replicas to use specific filters for
different sources. To configure a channel specific
replication filter on a channel named
<em class="replaceable">
<code>
channel_1
</code>
</em>
use
<code class="option">
--replicate-do-table:
<em class="replaceable">
<code>
channel_1
</code>
</em>
:
<em class="replaceable">
<code>
db_name.tbl_name
</code>
</em>
</code>
.
In this case, the first colon is interpreted as a separator
and subsequent colons are literal colons. See
<a class="xref" href="replication-rules-channel-based-filters.html" title="19.2.5.4 Replication Channel Based Filters">
Section 19.2.5.4, “Replication Channel Based Filters”
</a>
for more information.
</p>
<p>
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
Global replication filters cannot be used on a MySQL
server instance that is configured for Group
Replication, because filtering transactions on some
servers would make the group unable to reach agreement
on a consistent state. Channel specific replication
filters can be used on replication channels that are not
directly involved with Group Replication, such as where
a group member also acts as a replica to a source that
is outside the group. They cannot be used on the
<code class="literal">
group_replication_applier
</code>
or
<code class="literal">
group_replication_recovery
</code>
channels.
</p>
</div>
<p>
</p>
<p>
This option affects only statements that apply to tables. It
does not affect statements that apply only to other database
objects, such as stored routines. To filter statements
operating on stored routines, use one or more of the
<code class="option">
--replicate-*-db
</code>
options.
</p>
</li>
<li class="listitem">
<p>
<a name="option_mysqld_replicate-ignore-table">
</a>
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-ignore-table">
<code class="option">
--replicate-ignore-table=
<em class="replaceable">
<code>
db_name.tbl_name
</code>
</em>
</code>
</a>
</p>
<a class="indexterm" name="idm46045143590192">
</a>
<a class="indexterm" name="idm46045143588688">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for replicate-ignore-table">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--replicate-ignore-table=name
</code>
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
String
</td>
</tr>
</tbody>
</table>
</div>
<p>
Creates a replication filter by telling the replication SQL
thread not to replicate any statement that updates the
specified table, even if any other tables might be updated
by the same statement. To specify more than one table to
ignore, use this option multiple times, once for each table.
This works for cross-database updates, in contrast to
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-ignore-db">
<code class="option">
--replicate-ignore-db
</code>
</a>
. See
<a class="xref" href="replication-rules.html" title="19.2.5 How Servers Evaluate Replication Filtering Rules">
Section 19.2.5, “How Servers Evaluate Replication Filtering Rules”
</a>
. You can also create
such a filter by issuing a
<a class="link" href="change-replication-filter.html" title="15.4.2.1 CHANGE REPLICATION FILTER Statement">
<code class="literal">
CHANGE
REPLICATION FILTER REPLICATE_IGNORE_TABLE
</code>
</a>
statement.
</p>
<p>
This option supports channel specific replication filters,
enabling multi-source replicas to use specific filters for
different sources. To configure a channel specific
replication filter on a channel named
<em class="replaceable">
<code>
channel_1
</code>
</em>
use
<code class="option">
--replicate-ignore-table:
<em class="replaceable">
<code>
channel_1
</code>
</em>
:
<em class="replaceable">
<code>
db_name.tbl_name
</code>
</em>
</code>
.
In this case, the first colon is interpreted as a separator
and subsequent colons are literal colons. See
<a class="xref" href="replication-rules-channel-based-filters.html" title="19.2.5.4 Replication Channel Based Filters">
Section 19.2.5.4, “Replication Channel Based Filters”
</a>
for more information.
</p>
<p>
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
Global replication filters cannot be used on a MySQL
server instance that is configured for Group
Replication, because filtering transactions on some
servers would make the group unable to reach agreement
on a consistent state. Channel specific replication
filters can be used on replication channels that are not
directly involved with Group Replication, such as where
a group member also acts as a replica to a source that
is outside the group. They cannot be used on the
<code class="literal">
group_replication_applier
</code>
or
<code class="literal">
group_replication_recovery
</code>
channels.
</p>
</div>
<p>
</p>
<p>
This option affects only statements that apply to tables. It
does not affect statements that apply only to other database
objects, such as stored routines. To filter statements
operating on stored routines, use one or more of the
<code class="option">
--replicate-*-db
</code>
options.
</p>
</li>
<li class="listitem">
<p>
<a name="option_mysqld_replicate-rewrite-db">
</a>
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-rewrite-db">
<code class="option">
--replicate-rewrite-db=
<em class="replaceable">
<code>
from_name
</code>
</em>
->
<em class="replaceable">
<code>
to_name
</code>
</em>
</code>
</a>
</p>
<a class="indexterm" name="idm46045143564592">
</a>
<a class="indexterm" name="idm46045143563136">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for replicate-rewrite-db">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--replicate-rewrite-db=old_name->new_name
</code>
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
String
</td>
</tr>
</tbody>
</table>
</div>
<p>
Tells the replica to create a replication filter that
translates the specified database to
<em class="replaceable">
<code>
to_name
</code>
</em>
if it was
<em class="replaceable">
<code>
from_name
</code>
</em>
on the source. Only
statements involving tables are affected, not statements
such as
<a class="link" href="create-database.html" title="15.1.12 CREATE DATABASE Statement">
<code class="literal">
CREATE DATABASE
</code>
</a>
,
<a class="link" href="drop-database.html" title="15.1.24 DROP DATABASE Statement">
<code class="literal">
DROP DATABASE
</code>
</a>
, and
<a class="link" href="alter-database.html" title="15.1.2 ALTER DATABASE Statement">
<code class="literal">
ALTER DATABASE
</code>
</a>
.
</p>
<p>
To specify multiple rewrites, use this option multiple
times. The server uses the first one with a
<em class="replaceable">
<code>
from_name
</code>
</em>
value that matches. The
database name translation is done
<span class="emphasis">
<em>
before
</em>
</span>
the
<code class="option">
--replicate-*
</code>
rules are tested. You can
also create such a filter by issuing a
<a class="link" href="change-replication-filter.html" title="15.4.2.1 CHANGE REPLICATION FILTER Statement">
<code class="literal">
CHANGE
REPLICATION FILTER REPLICATE_REWRITE_DB
</code>
</a>
statement.
</p>
<p>
If you use the
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-rewrite-db">
<code class="option">
--replicate-rewrite-db
</code>
</a>
option
on the command line and the
<code class="literal">
>
</code>
character is special to your command interpreter, quote the
option value. For example:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-terminal"><div class="docs-select-all right" id="sa91628357"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-terminal"><span class="token prompt">$> </span><span class="token command">mysqld</span> <span class="token constant">--replicate-rewrite-db</span>=<span class="token atrule">"<em class="replaceable">olddb</em>-><em class="replaceable">newdb</em>"</span></code></pre>
</div>
<p>
The effect of the
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-rewrite-db">
<code class="option">
--replicate-rewrite-db
</code>
</a>
option
differs depending on whether statement-based or row-based
binary logging format is used for the query. With
statement-based format, DML statements are translated based
on the current database, as specified by the
<a class="link" href="use.html" title="15.8.4 USE Statement">
<code class="literal">
USE
</code>
</a>
statement. With row-based
format, DML statements are translated based on the database
where the modified table exists. DDL statements are always
filtered based on the current database, as specified by the
<a class="link" href="use.html" title="15.8.4 USE Statement">
<code class="literal">
USE
</code>
</a>
statement, regardless of
the binary logging format.
</p>
<p>
To ensure that rewriting produces the expected results,
particularly in combination with other replication filtering
options, follow these recommendations when you use the
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-rewrite-db">
<code class="option">
--replicate-rewrite-db
</code>
</a>
option:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<p>
Create the
<em class="replaceable">
<code>
from_name
</code>
</em>
and
<em class="replaceable">
<code>
to_name
</code>
</em>
databases manually on
the source and the replica with different names.
</p>
</li>
<li class="listitem">
<p>
If you use statement-based or mixed binary logging
format, do not use cross-database queries, and do not
specify database names in queries. For both DDL and DML
statements, rely on the
<a class="link" href="use.html" title="15.8.4 USE Statement">
<code class="literal">
USE
</code>
</a>
statement to specify
the current database, and use only the table name in
queries.
</p>
</li>
<li class="listitem">
<p>
If you use row-based binary logging format exclusively,
for DDL statements, rely on the
<a class="link" href="use.html" title="15.8.4 USE Statement">
<code class="literal">
USE
</code>
</a>
statement to specify
the current database, and use only the table name in
queries. For DML statements, you can use a fully
qualified table name
(
<em class="replaceable">
<code>
db
</code>
</em>
.
<em class="replaceable">
<code>
table
</code>
</em>
)
if you want.
</p>
</li>
</ul>
</div>
<p>
If these recommendations are followed, it is safe to use the
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-rewrite-db">
<code class="option">
--replicate-rewrite-db
</code>
</a>
option
in combination with table-level replication filtering
options such as
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-do-table">
<code class="option">
--replicate-do-table
</code>
</a>
.
</p>
<p>
This option supports channel specific replication filters,
enabling multi-source replicas to use specific filters for
different sources. Specify the channel name followed by a
colon, followed by the filter specification. The first colon
is interpreted as a separator, and any subsequent colons are
interpreted as literal colons. For example, to configure a
channel specific replication filter on a channel named
<em class="replaceable">
<code>
channel_1
</code>
</em>
, use:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-terminal"><div class="docs-select-all right" id="sa73814727"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-terminal"><span class="token prompt">$> </span><span class="token command">mysqld</span> <span class="token constant">--replicate-rewrite-db</span><span class="token attr-value"><span class="token punctuation">=</span><em class="replaceable">channel_1</em>:<em class="replaceable">db_name1</em>-><em class="replaceable">db_name2</em></span></code></pre>
</div>
<p>
If you use a colon but do not specify a channel name, the
option configures the replication filter for the default
replication channel. See
<a class="xref" href="replication-rules-channel-based-filters.html" title="19.2.5.4 Replication Channel Based Filters">
Section 19.2.5.4, “Replication Channel Based Filters”
</a>
for more information.
</p>
<p>
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
Global replication filters cannot be used on a MySQL
server instance that is configured for Group
Replication, because filtering transactions on some
servers would make the group unable to reach agreement
on a consistent state. Channel specific replication
filters can be used on replication channels that are not
directly involved with Group Replication, such as where
a group member also acts as a replica to a source that
is outside the group. They cannot be used on the
<code class="literal">
group_replication_applier
</code>
or
<code class="literal">
group_replication_recovery
</code>
channels.
</p>
</div>
<p>
</p>
</li>
<li class="listitem">
<p>
<a name="option_mysqld_replicate-same-server-id">
</a>
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-same-server-id">
<code class="option">
--replicate-same-server-id
</code>
</a>
</p>
<a class="indexterm" name="idm46045143513472">
</a>
<a class="indexterm" name="idm46045143511968">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for replicate-same-server-id">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--replicate-same-server-id[={OFF|ON}]
</code>
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Boolean
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
OFF
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
This option is for use on replicas. The default is 0
(
<code class="literal">
FALSE
</code>
). With this option set to 1
(
<code class="literal">
TRUE
</code>
), the replica does not skip events
that have its own server ID. This setting is normally useful
only in rare configurations.
</p>
<p>
When binary logging is enabled on a replica, the combination
of the
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-same-server-id">
<code class="option">
--replicate-same-server-id
</code>
</a>
and
<a class="link" href="replication-options-binary-log.html#sysvar_log_replica_updates">
<code class="option">
--log-replica-updates
</code>
</a>
options on the replica can cause infinite loops in
replication if the server is part of a circular replication
topology. (In MySQL 8.4, binary logging is
enabled by default, and replica update logging is the
default when binary logging is enabled.) However, the use of
global transaction identifiers (GTIDs) prevents this
situation by skipping the execution of transactions that
have already been applied. If
<a class="link" href="replication-options-gtids.html#sysvar_gtid_mode">
<code class="literal">
gtid_mode=ON
</code>
</a>
is set on the
replica, you can start the server with this combination of
options, but you cannot change to any other GTID mode while
the server is running. If any other GTID mode is set, the
server does not start with this combination of options.
</p>
<p>
By default, the replication I/O (receiver) thread does not
write binary log events to the relay log if they have the
replica's server ID (this optimization helps save disk
usage). If you want to use
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-same-server-id">
<code class="option">
--replicate-same-server-id
</code>
</a>
,
be sure to start the replica with this option before you
make the replica read its own events that you want the
replication SQL (applier) thread to execute.
</p>
</li>
<li class="listitem">
<p>
<a name="option_mysqld_replicate-wild-do-table">
</a>
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-wild-do-table">
<code class="option">
--replicate-wild-do-table=
<em class="replaceable">
<code>
db_name.tbl_name
</code>
</em>
</code>
</a>
</p>
<a class="indexterm" name="idm46045143489488">
</a>
<a class="indexterm" name="idm46045143487984">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for replicate-wild-do-table">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--replicate-wild-do-table=name
</code>
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
String
</td>
</tr>
</tbody>
</table>
</div>
<p>
Creates a replication filter by telling the replication SQL
(applier) thread to restrict replication to statements where
any of the updated tables match the specified database and
table name patterns. Patterns can contain the
<code class="literal">
%
</code>
and
<code class="literal">
_
</code>
wildcard
characters, which have the same meaning as for the
<a class="link" href="string-comparison-functions.html#operator_like">
<code class="literal">
LIKE
</code>
</a>
pattern-matching operator.
To specify more than one table, use this option multiple
times, once for each table. This works for cross-database
updates. See
<a class="xref" href="replication-rules.html" title="19.2.5 How Servers Evaluate Replication Filtering Rules">
Section 19.2.5, “How Servers Evaluate Replication Filtering Rules”
</a>
. You can
also create such a filter by issuing a
<a class="link" href="change-replication-filter.html" title="15.4.2.1 CHANGE REPLICATION FILTER Statement">
<code class="literal">
CHANGE
REPLICATION FILTER REPLICATE_WILD_DO_TABLE
</code>
</a>
statement.
</p>
<p>
This option supports channel specific replication filters,
enabling multi-source replicas to use specific filters for
different sources. To configure a channel specific
replication filter on a channel named
<em class="replaceable">
<code>
channel_1
</code>
</em>
use
<code class="option">
--replicate-wild-do-table:
<em class="replaceable">
<code>
channel_1
</code>
</em>
:
<em class="replaceable">
<code>
db_name.tbl_name
</code>
</em>
</code>
.
In this case, the first colon is interpreted as a separator
and subsequent colons are literal colons. See
<a class="xref" href="replication-rules-channel-based-filters.html" title="19.2.5.4 Replication Channel Based Filters">
Section 19.2.5.4, “Replication Channel Based Filters”
</a>
for more information.
</p>
<div class="important" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Important
</div>
<p>
Global replication filters cannot be used on a MySQL
server instance that is configured for Group Replication,
because filtering transactions on some servers would make
the group unable to reach agreement on a consistent state.
Channel specific replication filters can be used on
replication channels that are not directly involved with
Group Replication, such as where a group member also acts
as a replica to a source that is outside the group. They
cannot be used on the
<code class="literal">
group_replication_applier
</code>
or
<code class="literal">
group_replication_recovery
</code>
channels.
</p>
</div>
<p>
The replication filter specified by the
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-wild-do-table">
<code class="option">
--replicate-wild-do-table
</code>
</a>
option applies to tables, views, and triggers. It does not
apply to stored procedures and functions, or events. To
filter statements operating on the latter objects, use one
or more of the
<code class="option">
--replicate-*-db
</code>
options.
</p>
<p>
As an example,
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-wild-do-table">
<code class="option">
--replicate-wild-do-table=foo%.bar%
</code>
</a>
replicates only updates that use a table where the database
name starts with
<code class="literal">
foo
</code>
and the table name
starts with
<code class="literal">
bar
</code>
.
</p>
<p>
If the table name pattern is
<code class="literal">
%
</code>
, it
matches any table name and the option also applies to
database-level statements (
<a class="link" href="create-database.html" title="15.1.12 CREATE DATABASE Statement">
<code class="literal">
CREATE
DATABASE
</code>
</a>
,
<a class="link" href="drop-database.html" title="15.1.24 DROP DATABASE Statement">
<code class="literal">
DROP
DATABASE
</code>
</a>
, and
<a class="link" href="alter-database.html" title="15.1.2 ALTER DATABASE Statement">
<code class="literal">
ALTER
DATABASE
</code>
</a>
). For example, if you use
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-wild-do-table">
<code class="option">
--replicate-wild-do-table=foo%.%
</code>
</a>
,
database-level statements are replicated if the database
name matches the pattern
<code class="literal">
foo%
</code>
.
</p>
<div class="important" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Important
</div>
<p>
Table-level replication filters are only applied to tables
that are explicitly mentioned and operated on in the
query. They do not apply to tables that are implicitly
updated by the query. For example, a
<a class="link" href="grant.html" title="15.7.1.6 GRANT Statement">
<code class="literal">
GRANT
</code>
</a>
statement, which
updates the
<code class="literal">
mysql.user
</code>
system table but
does not mention that table, is not affected by a filter
that specifies
<code class="literal">
mysql.%
</code>
as the wildcard
pattern.
</p>
</div>
<p>
To include literal wildcard characters in the database or
table name patterns, escape them with a backslash. For
example, to replicate all tables of a database that is named
<code class="literal">
my_own%db
</code>
, but not replicate tables from
the
<code class="literal">
my1ownAABCdb
</code>
database, you should
escape the
<code class="literal">
_
</code>
and
<code class="literal">
%
</code>
characters like this:
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-wild-do-table">
<code class="option">
--replicate-wild-do-table=my\_own\%db
</code>
</a>
.
If you use the option on the command line, you might need to
double the backslashes or quote the option value, depending
on your command interpreter. For example, with the
<span class="command">
<strong>
bash
</strong>
</span>
shell, you would need to type
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-wild-do-table">
<code class="option">
--replicate-wild-do-table=my\\_own\\%db
</code>
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a name="option_mysqld_replicate-wild-ignore-table">
</a>
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-wild-ignore-table">
<code class="option">
--replicate-wild-ignore-table=
<em class="replaceable">
<code>
db_name.tbl_name
</code>
</em>
</code>
</a>
</p>
<a class="indexterm" name="idm46045143442448">
</a>
<a class="indexterm" name="idm46045143440944">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for replicate-wild-ignore-table">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--replicate-wild-ignore-table=name
</code>
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
String
</td>
</tr>
</tbody>
</table>
</div>
<p>
Creates a replication filter which keeps the replication SQL
thread from replicating a statement in which any table
matches the given wildcard pattern. To specify more than one
table to ignore, use this option multiple times, once for
each table. This works for cross-database updates. See
<a class="xref" href="replication-rules.html" title="19.2.5 How Servers Evaluate Replication Filtering Rules">
Section 19.2.5, “How Servers Evaluate Replication Filtering Rules”
</a>
. You can also create
such a filter by issuing a
<a class="link" href="change-replication-filter.html" title="15.4.2.1 CHANGE REPLICATION FILTER Statement">
<code class="literal">
CHANGE
REPLICATION FILTER REPLICATE_WILD_IGNORE_TABLE
</code>
</a>
statement.
</p>
<p>
This option supports channel specific replication filters,
enabling multi-source replicas to use specific filters for
different sources. To configure a channel specific
replication filter on a channel named
<em class="replaceable">
<code>
channel_1
</code>
</em>
use
<code class="option">
--replicate-wild-ignore:
<em class="replaceable">
<code>
channel_1
</code>
</em>
:
<em class="replaceable">
<code>
db_name.tbl_name
</code>
</em>
</code>
.
In this case, the first colon is interpreted as a separator
and subsequent colons are literal colons. See
<a class="xref" href="replication-rules-channel-based-filters.html" title="19.2.5.4 Replication Channel Based Filters">
Section 19.2.5.4, “Replication Channel Based Filters”
</a>
for more information.
</p>
<div class="important" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Important
</div>
<p>
Global replication filters cannot be used on a MySQL
server instance that is configured for Group Replication,
because filtering transactions on some servers would make
the group unable to reach agreement on a consistent state.
Channel specific replication filters can be used on
replication channels that are not directly involved with
Group Replication, such as where a group member also acts
as a replica to a source that is outside the group. They
cannot be used on the
<code class="literal">
group_replication_applier
</code>
or
<code class="literal">
group_replication_recovery
</code>
channels.
</p>
</div>
<p>
As an example,
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-wild-ignore-table">
<code class="option">
--replicate-wild-ignore-table=foo%.bar%
</code>
</a>
does not replicate updates that use a table where the
database name starts with
<code class="literal">
foo
</code>
and the
table name starts with
<code class="literal">
bar
</code>
. For
information about how matching works, see the description of
the
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-wild-do-table">
<code class="option">
--replicate-wild-do-table
</code>
</a>
option. The rules for including literal wildcard characters
in the option value are the same as for
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-wild-ignore-table">
<code class="option">
--replicate-wild-ignore-table
</code>
</a>
as well.
</p>
<div class="important" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Important
</div>
<p>
Table-level replication filters are only applied to tables
that are explicitly mentioned and operated on in the
query. They do not apply to tables that are implicitly
updated by the query. For example, a
<a class="link" href="grant.html" title="15.7.1.6 GRANT Statement">
<code class="literal">
GRANT
</code>
</a>
statement, which
updates the
<code class="literal">
mysql.user
</code>
system table but
does not mention that table, is not affected by a filter
that specifies
<code class="literal">
mysql.%
</code>
as the wildcard
pattern.
</p>
</div>
<p>
If you need to filter out
<a class="link" href="grant.html" title="15.7.1.6 GRANT Statement">
<code class="literal">
GRANT
</code>
</a>
statements or other
administrative statements, a possible workaround is to use
the
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-ignore-db">
<code class="option">
--replicate-ignore-db
</code>
</a>
filter. This filter operates on the default database that is
currently in effect, as determined by the
<a class="link" href="use.html" title="15.8.4 USE Statement">
<code class="literal">
USE
</code>
</a>
statement. You can
therefore create a filter to ignore statements for a
database that is not replicated, then issue the
<a class="link" href="use.html" title="15.8.4 USE Statement">
<code class="literal">
USE
</code>
</a>
statement
to switch the default database to that one immediately
before issuing any administrative statements that you want
to ignore. In the administrative statement, name the actual
database where the statement is applied.
</p>
<p>
For example, if
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-ignore-db">
<code class="option">
--replicate-ignore-db=nonreplicated
</code>
</a>
is configured on the replica server, the following sequence
of statements causes the
<a class="link" href="grant.html" title="15.7.1.6 GRANT Statement">
<code class="literal">
GRANT
</code>
</a>
statement to be
ignored, because the default database
<code class="literal">
nonreplicated
</code>
is in effect:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa3861993"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">USE</span> nonreplicated<span class="token punctuation">;</span>
<span class="token keyword">GRANT</span> <span class="token keyword">SELECT</span><span class="token punctuation">,</span> <span class="token keyword">INSERT</span> <span class="token keyword">ON</span> replicated<span class="token punctuation">.</span>t1 <span class="token keyword">TO</span> <span class="token string">'someuser'</span>@<span class="token string">'somehost'</span><span class="token punctuation">;</span></code></pre>
</div>
</li>
<li class="listitem">
<p>
<a name="option_mysqld_skip-replica-start">
</a>
<a class="link" href="replication-options-replica.html#option_mysqld_skip-replica-start">
<code class="option">
--skip-replica-start
</code>
</a>
</p>
<a class="indexterm" name="idm46045143401488">
</a>
<a class="indexterm" name="idm46045143400032">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for skip-replica-start">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--skip-replica-start[={OFF|ON}]
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_skip_replica_start">
skip_replica_start
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
No
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Boolean
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
OFF
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
<a class="link" href="replication-options-replica.html#option_mysqld_skip-replica-start">
<code class="option">
--skip-replica-start
</code>
</a>
tells
the replica server not to start the replication I/O
(receiver) and SQL (applier) threads when the server starts.
To start the threads later, use a
<a class="link" href="start-replica.html" title="15.4.2.4 START REPLICA Statement">
<code class="literal">
START
REPLICA
</code>
</a>
statement.
</p>
<p>
You can use the
<a class="link" href="replication-options-replica.html#sysvar_skip_replica_start">
<code class="literal">
skip_replica_start
</code>
</a>
system
variable in place of the command line option to allow access
to this feature using MySQL Server’s privilege structure,
so that database administrators do not need any privileged
access to the operating system.
</p>
</li>
<li class="listitem">
<p>
<a name="option_mysqld_skip-slave-start">
</a>
<a class="link" href="replication-options-replica.html#option_mysqld_skip-slave-start">
<code class="option">
--skip-slave-start
</code>
</a>
</p>
<a class="indexterm" name="idm46045143371152">
</a>
<a class="indexterm" name="idm46045143369664">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for skip-slave-start">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--skip-slave-start[={OFF|ON}]
</code>
</td>
</tr>
<tr>
<th>
Deprecated
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_skip_slave_start">
skip_slave_start
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
No
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Boolean
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
OFF
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
Deprecated alias for
<a class="link" href="replication-options-replica.html#option_mysqld_skip-replica-start">
<code class="option">
--skip-replica-start
</code>
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a name="option_mysqld_slave-skip-errors">
</a>
<a class="link" href="replication-options-replica.html#option_mysqld_slave-skip-errors">
<code class="option">
--slave-skip-errors=[
<em class="replaceable">
<code>
err_code1
</code>
</em>
,
<em class="replaceable">
<code>
err_code2
</code>
</em>
,...|all|ddl_exist_errors]
</code>
</a>
</p>
<a class="indexterm" name="idm46045143341472">
</a>
<a class="indexterm" name="idm46045143339968">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for slave-skip-errors">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--slave-skip-errors=name
</code>
</td>
</tr>
<tr>
<th>
Deprecated
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_slave_skip_errors">
slave_skip_errors
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
No
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
String
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
OFF
</code>
</td>
</tr>
<tr>
<th>
Valid Values
</th>
<td>
<p class="valid-value">
<code class="literal">
OFF
</code>
</p>
<p class="valid-value">
<code class="literal">
[list of error codes]
</code>
</p>
<p class="valid-value">
<code class="literal">
all
</code>
</p>
<p class="valid-value">
<code class="literal">
ddl_exist_errors
</code>
</p>
</td>
</tr>
</tbody>
</table>
</div>
<p>
Deprecated synonym for
<a class="link" href="replication-options-replica.html#sysvar_replica_skip_errors">
<code class="option">
--replica-skip-errors
</code>
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a name="option_mysqld_slave-sql-verify-checksum">
</a>
<a class="link" href="replication-options-replica.html#option_mysqld_slave-sql-verify-checksum">
<code class="option">
--slave-sql-verify-checksum={0|1}
</code>
</a>
</p>
<a class="indexterm" name="idm46045143306880">
</a>
<a class="indexterm" name="idm46045143305376">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for slave-sql-verify-checksum">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--slave-sql-verify-checksum[={OFF|ON}]
</code>
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Boolean
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
ON
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
Deprecated synonym for
<a class="link" href="replication-options-replica.html#sysvar_replica_sql_verify_checksum">
<code class="option">
--replica-sql-verify-checksum
</code>
</a>
</p>
</li>
</ul>
</div>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h5 class="title">
<a name="replication-sysvars-slaves">
</a>
System Variables Used on Replica Servers
</h5>
</div>
</div>
</div>
<p>
The following list describes system variables for controlling
replica servers. They can be set at server startup and some of
them can be changed at runtime using
<a class="link" href="set-variable.html" title="15.7.6.1 SET Syntax for Variable Assignment">
<code class="literal">
SET
</code>
</a>
.
Server options used with replicas are listed earlier in this
section.
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<a name="sysvar_init_replica">
</a>
<a class="link" href="replication-options-replica.html#sysvar_init_replica">
<code class="literal">
init_replica
</code>
</a>
</p>
<a class="indexterm" name="idm46045143286544">
</a>
<a class="indexterm" name="idm46045143285456">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for init_replica">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--init-replica=name
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_init_replica">
init_replica
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
String
</td>
</tr>
</tbody>
</table>
</div>
<p>
<a class="link" href="replication-options-replica.html#sysvar_init_replica">
<code class="literal">
init_replica
</code>
</a>
is similar to
<a class="link" href="server-system-variables.html#sysvar_init_connect">
<code class="literal">
init_connect
</code>
</a>
, but is a
string to be executed by a replica server each time the
replication SQL thread starts. The format of the string is
the same as for the
<a class="link" href="server-system-variables.html#sysvar_init_connect">
<code class="literal">
init_connect
</code>
</a>
variable. The
setting of this variable takes effect for subsequent
<a class="link" href="start-replica.html" title="15.4.2.4 START REPLICA Statement">
<code class="literal">
START REPLICA
</code>
</a>
statements.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
The replication SQL thread sends an acknowledgment to the
client before it executes
<a class="link" href="replication-options-replica.html#sysvar_init_replica">
<code class="literal">
init_replica
</code>
</a>
. Therefore,
it is not guaranteed that
<a class="link" href="replication-options-replica.html#sysvar_init_replica">
<code class="literal">
init_replica
</code>
</a>
has been
executed when
<a class="link" href="start-replica.html" title="15.4.2.4 START REPLICA Statement">
<code class="literal">
START REPLICA
</code>
</a>
returns. See
<a class="xref" href="start-replica.html" title="15.4.2.4 START REPLICA Statement">
Section 15.4.2.4, “START REPLICA Statement”
</a>
for more
information.
</p>
</div>
</li>
<li class="listitem">
<p>
<a name="sysvar_init_slave">
</a>
<a class="link" href="replication-options-replica.html#sysvar_init_slave">
<code class="literal">
init_slave
</code>
</a>
</p>
<a class="indexterm" name="idm46045143252976">
</a>
<a class="indexterm" name="idm46045143251888">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for init_slave">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--init-slave=name
</code>
</td>
</tr>
<tr>
<th>
Deprecated
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_init_slave">
init_slave
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
String
</td>
</tr>
</tbody>
</table>
</div>
<p>
Deprecated alias for
<a class="link" href="replication-options-replica.html#sysvar_init_replica">
<code class="literal">
init_replica
</code>
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_log_slow_replica_statements">
</a>
<a class="link" href="replication-options-replica.html#sysvar_log_slow_replica_statements">
<code class="literal">
log_slow_replica_statements
</code>
</a>
</p>
<a class="indexterm" name="idm46045143226608">
</a>
<a class="indexterm" name="idm46045143225504">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for log_slow_replica_statements">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--log-slow-replica-statements[={OFF|ON}]
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_log_slow_replica_statements">
log_slow_replica_statements
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Boolean
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
OFF
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
When the slow query log is enabled,
<a class="link" href="replication-options-replica.html#sysvar_log_slow_replica_statements">
<code class="literal">
log_slow_replica_statements
</code>
</a>
enables logging for queries that have taken more than
<a class="link" href="server-system-variables.html#sysvar_long_query_time">
<code class="literal">
long_query_time
</code>
</a>
seconds to
execute on the replica. Note that if row-based replication
is in use
(
<a class="link" href="replication-options-binary-log.html#sysvar_binlog_format">
<code class="literal">
binlog_format=ROW
</code>
</a>
),
<a class="link" href="replication-options-replica.html#sysvar_log_slow_replica_statements">
<code class="literal">
log_slow_replica_statements
</code>
</a>
has no effect. Queries are only added to the replica's slow
query log when they are logged in statement format in the
binary log, that is, when
<a class="link" href="replication-options-binary-log.html#sysvar_binlog_format">
<code class="literal">
binlog_format=STATEMENT
</code>
</a>
is
set, or when
<a class="link" href="replication-options-binary-log.html#sysvar_binlog_format">
<code class="literal">
binlog_format=MIXED
</code>
</a>
is set
and the statement is logged in statement format. Slow
queries that are logged in row format when
<a class="link" href="replication-options-binary-log.html#sysvar_binlog_format">
<code class="literal">
binlog_format=MIXED
</code>
</a>
is set,
or that are logged when
<a class="link" href="replication-options-binary-log.html#sysvar_binlog_format">
<code class="literal">
binlog_format=ROW
</code>
</a>
is set,
are not added to the replica's slow query log, even if
<a class="link" href="replication-options-replica.html#sysvar_log_slow_replica_statements">
<code class="literal">
log_slow_replica_statements
</code>
</a>
is enabled.
</p>
<p>
Setting
<a class="link" href="replication-options-replica.html#sysvar_log_slow_replica_statements">
<code class="literal">
log_slow_replica_statements
</code>
</a>
has no immediate effect. The state of the variable applies
on all subsequent
<a class="link" href="start-replica.html" title="15.4.2.4 START REPLICA Statement">
<code class="literal">
START
REPLICA
</code>
</a>
statements. Also note that the global
setting for
<a class="link" href="server-system-variables.html#sysvar_long_query_time">
<code class="literal">
long_query_time
</code>
</a>
applies for the lifetime of the SQL thread. If you change
that setting, you must stop and restart the replication SQL
thread to implement the change there (for example, by
issuing
<a class="link" href="stop-replica.html" title="15.4.2.5 STOP REPLICA Statement">
<code class="literal">
STOP REPLICA
</code>
</a>
and
<a class="link" href="start-replica.html" title="15.4.2.4 START REPLICA Statement">
<code class="literal">
START REPLICA
</code>
</a>
statements with
the
<code class="literal">
SQL_THREAD
</code>
option).
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_log_slow_slave_statements">
</a>
<a class="link" href="replication-options-replica.html#sysvar_log_slow_slave_statements">
<code class="literal">
log_slow_slave_statements
</code>
</a>
</p>
<a class="indexterm" name="idm46045143181264">
</a>
<a class="indexterm" name="idm46045143180160">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for log_slow_slave_statements">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--log-slow-slave-statements[={OFF|ON}]
</code>
</td>
</tr>
<tr>
<th>
Deprecated
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_log_slow_slave_statements">
log_slow_slave_statements
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Boolean
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
OFF
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
Deprecated alias for
<a class="link" href="replication-options-replica.html#sysvar_log_slow_replica_statements">
<code class="literal">
log_slow_replica_statements
</code>
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_max_relay_log_size">
</a>
<a class="link" href="replication-options-replica.html#sysvar_max_relay_log_size">
<code class="literal">
max_relay_log_size
</code>
</a>
</p>
<a class="indexterm" name="idm46045143152288">
</a>
<a class="indexterm" name="idm46045143151248">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for max_relay_log_size">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--max-relay-log-size=#
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_max_relay_log_size">
max_relay_log_size
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Integer
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
0
</code>
</td>
</tr>
<tr>
<th>
Minimum Value
</th>
<td>
<code class="literal">
0
</code>
</td>
</tr>
<tr>
<th>
Maximum Value
</th>
<td>
<code class="literal">
1073741824
</code>
</td>
</tr>
<tr>
<th>
Unit
</th>
<td>
bytes
</td>
</tr>
<tr>
<th>
<a class="link" href="server-system-variables.html#system-variables-block-size" title="Note">
Block Size
</a>
</th>
<td>
<code class="literal">
4096
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
If a write by a replica to its relay log causes the current
log file size to exceed the value of this variable, the
replica rotates the relay logs (closes the current file and
opens the next one). If
<a class="link" href="replication-options-replica.html#sysvar_max_relay_log_size">
<code class="literal">
max_relay_log_size
</code>
</a>
is 0,
the server uses
<a class="link" href="replication-options-binary-log.html#sysvar_max_binlog_size">
<code class="literal">
max_binlog_size
</code>
</a>
for both
the binary log and the relay log. If
<a class="link" href="replication-options-replica.html#sysvar_max_relay_log_size">
<code class="literal">
max_relay_log_size
</code>
</a>
is
greater than 0, it constrains the size of the relay log,
which enables you to have different sizes for the two logs.
You must set
<a class="link" href="replication-options-replica.html#sysvar_max_relay_log_size">
<code class="literal">
max_relay_log_size
</code>
</a>
to
between 4096 bytes and 1GB (inclusive), or to 0. The default
value is 0. See
<a class="xref" href="replication-threads.html" title="19.2.3 Replication Threads">
Section 19.2.3, “Replication Threads”
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_relay_log">
</a>
<a class="link" href="replication-options-replica.html#sysvar_relay_log">
<code class="literal">
relay_log
</code>
</a>
</p>
<a class="indexterm" name="idm46045143110704">
</a>
<a class="indexterm" name="idm46045143109616">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for relay_log">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--relay-log=file_name
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_relay_log">
relay_log
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
No
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
File name
</td>
</tr>
</tbody>
</table>
</div>
<p>
The base name for relay log files. For the default
replication channel, the default base name for relay logs is
<code class="filename">
<em class="replaceable">
<code>
host_name
</code>
</em>
-relay-bin
</code>
.
For non-default replication channels, the default base name
for relay logs is
<code class="filename">
<em class="replaceable">
<code>
host_name
</code>
</em>
-relay-bin-
<em class="replaceable">
<code>
channel
</code>
</em>
</code>
,
where
<em class="replaceable">
<code>
channel
</code>
</em>
is the name of the
replication channel recorded in this relay log.
</p>
<p>
The server writes the file in the data directory unless the
base name is given with a leading absolute path name to
specify a different directory. The server creates relay log
files in sequence by adding a numeric suffix to the base
name.
</p>
<p>
The relay log and relay log index on a replication server
cannot be given the same names as the binary log and binary
log index, whose names are specified by the
<a class="link" href="replication-options-binary-log.html#option_mysqld_log-bin">
<code class="option">
--log-bin
</code>
</a>
and
<a class="link" href="replication-options-binary-log.html#option_mysqld_log-bin-index">
<code class="option">
--log-bin-index
</code>
</a>
options. The
server issues an error message and does not start if the
binary log and relay log file base names would be the same.
</p>
<p>
Due to the manner in which MySQL parses server options, if
you specify this variable at server startup, you must supply
a value;
<span class="emphasis">
<em>
the default base name is used only if the
option is not actually specified
</em>
</span>
. If you specify
the
<a class="link" href="replication-options-replica.html#sysvar_relay_log">
<code class="literal">
relay_log
</code>
</a>
system
variable at server startup without specifying a value,
unexpected behavior is likely to result; this behavior
depends on the other options used, the order in which they
are specified, and whether they are specified on the command
line or in an option file. For more information about how
MySQL handles server options, see
<a class="xref" href="program-options.html" title="6.2.2 Specifying Program Options">
Section 6.2.2, “Specifying Program Options”
</a>
.
</p>
<p>
If you specify this variable, the value specified is also
used as the base name for the relay log index file. You can
override this behavior by specifying a different relay log
index file base name using the
<a class="link" href="replication-options-replica.html#sysvar_relay_log_index">
<code class="literal">
relay_log_index
</code>
</a>
system
variable.
</p>
<p>
When the server reads an entry from the index file, it
checks whether the entry contains a relative path. If it
does, the relative part of the path is replaced with the
absolute path set using the
<a class="link" href="replication-options-replica.html#sysvar_relay_log">
<code class="literal">
relay_log
</code>
</a>
system variable.
An absolute path remains unchanged; in such a case, the
index must be edited manually to enable the new path or
paths to be used.
</p>
<p>
You may find the
<a class="link" href="replication-options-replica.html#sysvar_relay_log">
<code class="literal">
relay_log
</code>
</a>
system variable useful in performing the following tasks:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<p>
Creating relay logs whose names are independent of host
names.
</p>
</li>
<li class="listitem">
<p>
If you need to put the relay logs in some area other
than the data directory because your relay logs tend to
be very large and you do not want to decrease
<a class="link" href="replication-options-replica.html#sysvar_max_relay_log_size">
<code class="literal">
max_relay_log_size
</code>
</a>
.
</p>
</li>
<li class="listitem">
<p>
To increase speed by using load-balancing between disks.
</p>
</li>
</ul>
</div>
<p>
You can obtain the relay log file name (and path) from the
<a class="link" href="replication-options-replica.html#sysvar_relay_log_basename">
<code class="literal">
relay_log_basename
</code>
</a>
system
variable.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_relay_log_basename">
</a>
<a class="link" href="replication-options-replica.html#sysvar_relay_log_basename">
<code class="literal">
relay_log_basename
</code>
</a>
</p>
<a class="indexterm" name="idm46045143065728">
</a>
<a class="indexterm" name="idm46045143064688">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for relay_log_basename">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_relay_log_basename">
relay_log_basename
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
No
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
File name
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
datadir + '/' + hostname + '-relay-bin'
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
Holds the base name and complete path to the relay log file.
The maximum variable length is 256. This variable is set by
the server and is read only.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_relay_log_index">
</a>
<a class="link" href="replication-options-replica.html#sysvar_relay_log_index">
<code class="literal">
relay_log_index
</code>
</a>
</p>
<a class="indexterm" name="idm46045143042544">
</a>
<a class="indexterm" name="idm46045143041456">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for relay_log_index">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--relay-log-index=file_name
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_relay_log_index">
relay_log_index
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
No
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
File name
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
*host_name*-relay-bin.index
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
The name for the relay log index file. The maximum variable
length is 256. If you do not specify this variable, but the
<a class="link" href="replication-options-replica.html#sysvar_relay_log">
<code class="literal">
relay_log
</code>
</a>
system variable
is specified, its value is used as the default base name for
the relay log index file. If
<a class="link" href="replication-options-replica.html#sysvar_relay_log">
<code class="literal">
relay_log
</code>
</a>
is also not
specified, then for the default replication channel, the
default name is
<code class="filename">
<em class="replaceable">
<code>
host_name
</code>
</em>
-relay-bin.index
</code>
,
using the name of the host machine. For non-default
replication channels, the default name is
<code class="filename">
<em class="replaceable">
<code>
host_name
</code>
</em>
-relay-bin-
<em class="replaceable">
<code>
channel
</code>
</em>
.index
</code>
,
where
<em class="replaceable">
<code>
channel
</code>
</em>
is the name of the
replication channel recorded in this relay log index.
</p>
<p>
The default location for relay log files is the data
directory, or any other location that was specified using
the
<a class="link" href="replication-options-replica.html#sysvar_relay_log">
<code class="literal">
relay_log
</code>
</a>
system
variable. You can use the
<a class="link" href="replication-options-replica.html#sysvar_relay_log_index">
<code class="literal">
relay_log_index
</code>
</a>
system
variable to specify an alternative location, by adding a
leading absolute path name to the base name to specify a
different directory.
</p>
<p>
The relay log and relay log index on a replication server
cannot be given the same names as the binary log and binary
log index, whose names are specified by the
<a class="link" href="replication-options-binary-log.html#option_mysqld_log-bin">
<code class="option">
--log-bin
</code>
</a>
and
<a class="link" href="replication-options-binary-log.html#option_mysqld_log-bin-index">
<code class="option">
--log-bin-index
</code>
</a>
options. The
server issues an error message and does not start if the
binary log and relay log file base names would be the same.
</p>
<p>
Due to the manner in which MySQL parses server options, if
you specify this variable at server startup, you must supply
a value;
<span class="emphasis">
<em>
the default base name is used only if the
option is not actually specified
</em>
</span>
. If you specify
the
<a class="link" href="replication-options-replica.html#sysvar_relay_log_index">
<code class="literal">
relay_log_index
</code>
</a>
system
variable at server startup without specifying a value,
unexpected behavior is likely to result; this behavior
depends on the other options used, the order in which they
are specified, and whether they are specified on the command
line or in an option file. For more information about how
MySQL handles server options, see
<a class="xref" href="program-options.html" title="6.2.2 Specifying Program Options">
Section 6.2.2, “Specifying Program Options”
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_relay_log_purge">
</a>
<a class="link" href="replication-options-replica.html#sysvar_relay_log_purge">
<code class="literal">
relay_log_purge
</code>
</a>
</p>
<a class="indexterm" name="idm46045143001760">
</a>
<a class="indexterm" name="idm46045143000672">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for relay_log_purge">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--relay-log-purge[={OFF|ON}]
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_relay_log_purge">
relay_log_purge
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Boolean
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
ON
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
Disables or enables automatic purging of relay log files as
soon as they are not needed any more. The default value is 1
(
<code class="literal">
ON
</code>
).
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_relay_log_recovery">
</a>
<a class="link" href="replication-options-replica.html#sysvar_relay_log_recovery">
<code class="literal">
relay_log_recovery
</code>
</a>
</p>
<a class="indexterm" name="idm46045142975376">
</a>
<a class="indexterm" name="idm46045142973888">
</a>
<a class="indexterm" name="idm46045142972848">
</a>
<a class="indexterm" name="idm46045142971776">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for relay_log_recovery">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--relay-log-recovery[={OFF|ON}]
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_relay_log_recovery">
relay_log_recovery
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
No
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Boolean
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
OFF
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
If enabled, this variable enables automatic relay log
recovery immediately following server startup. The recovery
process creates a new relay log file, initializes the SQL
(applier) thread position to this new relay log, and
initializes the I/O (receiver) thread to the applier thread
position. Reading of the relay log from the source then
continues. If
<code class="literal">
SOURCE_AUTO_POSITION=1
</code>
was
set for the replication channel using a
<a class="link" href="change-replication-source-to.html" title="15.4.2.2 CHANGE REPLICATION SOURCE TO Statement">
<code class="literal">
CHANGE REPLICATION SOURCE TO
</code>
</a>
statement, the source position used to start replication
might be the one received in the connection and not the ones
assigned in this process.
</p>
<p>
When
<code class="literal">
relay_log_recovery
</code>
is disabled, the
server sanitizes the relay log on startup, by performing the
following actions:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<p>
Removing any transactions that remain uncompleted at the
end of the log
</p>
</li>
<li class="listitem">
<p>
Removing any relay log file which contains only parts of
unfinished transactions
</p>
</li>
<li class="listitem">
<p>
Removing any reference from the relay log index file to
any relay log file that has been removed
</p>
</li>
<li class="listitem">
<p>
When a valid source position and source filename are
obtained from the relay log, updating the position of
the receiver thread to match this file and position;
otherwise, updating the position of the receiver thread
to match the the position of the applier
</p>
</li>
</ul>
</div>
<p>
This global variable is read-only at runtime. Its value can
be set with the
<a class="link" href="replication-options-replica.html#sysvar_relay_log_recovery">
<code class="option">
--relay-log-recovery
</code>
</a>
option
at replica server startup, which should be used following an
unexpected halt of a replica to ensure that no possibly
corrupted relay logs are processed, and must be used in
order to guarantee a crash-safe replica. The default value
is 0 (disabled). For information on the combination of
settings on a replica that is most resilient to unexpected
halts, see
<a class="xref" href="replication-solutions-unexpected-replica-halt.html" title="19.4.2 Handling an Unexpected Halt of a Replica">
Section 19.4.2, “Handling an Unexpected Halt of a Replica”
</a>
.
</p>
<p>
For a multithreaded replica (where
<a class="link" href="replication-options-replica.html#sysvar_replica_parallel_workers">
<code class="literal">
replica_parallel_workers
</code>
</a>
is
greater than 0), setting
<a class="link" href="replication-options-replica.html#sysvar_relay_log_recovery">
<code class="option">
--relay-log-recovery
</code>
</a>
at
startup automatically handles any inconsistencies and gaps
in the sequence of transactions that have been executed from
the relay log. These gaps can occur when file position based
replication is in use. (For more details, see
<a class="xref" href="replication-features-transaction-inconsistencies.html" title="19.5.1.34 Replication and Transaction Inconsistencies">
Section 19.5.1.34, “Replication and Transaction Inconsistencies”
</a>
.)
The relay log recovery process deals with gaps using the
same method as the
<a class="link" href="start-replica.html" title="15.4.2.4 START REPLICA Statement">
<code class="literal">
START REPLICA
UNTIL SQL_AFTER_MTS_GAPS
</code>
</a>
statement would. When the
replica reaches a consistent gap-free state, the relay log
recovery process goes on to fetch further transactions from
the source beginning at the SQL (applier) thread position.
When GTID-based replication is in use, a multithreaded
replica checks first whether
<code class="literal">
SOURCE_AUTO_POSITION
</code>
is set to
<code class="literal">
ON
</code>
, and if it is, omits the step of
calculating the transactions that should be skipped or not
skipped, so that the old relay logs are not required for the
recovery process.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
This variable does not affect the following Group
Replication channels:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<p>
<code class="literal">
group_replication_applier
</code>
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
group_replication_recovery
</code>
</p>
</li>
</ul>
</div>
<p>
Any other channels running on a group are affected, such
as a channel which is replicating from an outside source
or another group.
</p>
</div>
</li>
<li class="listitem">
<p>
<a name="sysvar_relay_log_space_limit">
</a>
<a class="link" href="replication-options-replica.html#sysvar_relay_log_space_limit">
<code class="literal">
relay_log_space_limit
</code>
</a>
</p>
<a class="indexterm" name="idm46045142924512">
</a>
<a class="indexterm" name="idm46045142923472">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for relay_log_space_limit">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--relay-log-space-limit=#
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_relay_log_space_limit">
relay_log_space_limit
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
No
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Integer
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
0
</code>
</td>
</tr>
<tr>
<th>
Minimum Value
</th>
<td>
<code class="literal">
0
</code>
</td>
</tr>
<tr>
<th>
Maximum Value
</th>
<td>
<code class="literal">
18446744073709551615
</code>
</td>
</tr>
<tr>
<th>
Unit
</th>
<td>
bytes
</td>
</tr>
</tbody>
</table>
</div>
<p>
The maximum amount of space to use for all relay logs.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_replica_checkpoint_group">
</a>
<a class="link" href="replication-options-replica.html#sysvar_replica_checkpoint_group">
<code class="literal">
replica_checkpoint_group
</code>
</a>
</p>
<a class="indexterm" name="idm46045142892032">
</a>
<a class="indexterm" name="idm46045142890528">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for replica_checkpoint_group">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--replica-checkpoint-group=#
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_replica_checkpoint_group">
replica_checkpoint_group
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Integer
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
512
</code>
</td>
</tr>
<tr>
<th>
Minimum Value
</th>
<td>
<code class="literal">
32
</code>
</td>
</tr>
<tr>
<th>
Maximum Value
</th>
<td>
<code class="literal">
524280
</code>
</td>
</tr>
<tr>
<th>
<a class="link" href="server-system-variables.html#system-variables-block-size" title="Note">
Block Size
</a>
</th>
<td>
<code class="literal">
8
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
<a class="link" href="replication-options-replica.html#sysvar_replica_checkpoint_group">
<code class="literal">
replica_checkpoint_group
</code>
</a>
sets the maximum number of transactions that can be
processed by a multithreaded replica before a checkpoint
operation is called to update its status as shown by
<a class="link" href="show-replica-status.html" title="15.7.7.35 SHOW REPLICA STATUS Statement">
<code class="literal">
SHOW REPLICA STATUS
</code>
</a>
. Setting
this variable has no effect on replicas for which
multithreading is not enabled. Setting this variable has no
immediate effect. The state of the variable applies to all
subsequent
<a class="link" href="start-replica.html" title="15.4.2.4 START REPLICA Statement">
<code class="literal">
START REPLICA
</code>
</a>
statements.
</p>
<p>
This variable works in combination with the
<a class="link" href="replication-options-replica.html#sysvar_replica_checkpoint_period">
<code class="literal">
replica_checkpoint_period
</code>
</a>
system variable in such a way that, when either limit is
exceeded, the checkpoint is executed and the counters
tracking both the number of transactions and the time
elapsed since the last checkpoint are reset.
</p>
<p>
The minimum allowed value for this variable is 32, unless
the server was built using
<a class="link" href="source-configuration-options.html#option_cmake_with_debug">
<code class="option">
-DWITH_DEBUG
</code>
</a>
, in which case
the minimum value is 1. The effective value is always a
multiple of 8; you can set it to a value that is not such a
multiple, but the server rounds it down to the next lower
multiple of 8 before storing the value.
(
<span class="emphasis">
<em>
Exception
</em>
</span>
: No such rounding is
performed by the debug server.) Regardless of how the server
was built, the default value is 512, and the maximum allowed
value is 524280.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_replica_checkpoint_period">
</a>
<a class="link" href="replication-options-replica.html#sysvar_replica_checkpoint_period">
<code class="literal">
replica_checkpoint_period
</code>
</a>
</p>
<a class="indexterm" name="idm46045142850064">
</a>
<a class="indexterm" name="idm46045142848560">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for replica_checkpoint_period">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--replica-checkpoint-period=#
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_replica_checkpoint_period">
replica_checkpoint_period
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Integer
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
300
</code>
</td>
</tr>
<tr>
<th>
Minimum Value
</th>
<td>
<code class="literal">
1
</code>
</td>
</tr>
<tr>
<th>
Maximum Value
</th>
<td>
<code class="literal">
4294967295
</code>
</td>
</tr>
<tr>
<th>
Unit
</th>
<td>
milliseconds
</td>
</tr>
</tbody>
</table>
</div>
<p>
<code class="literal">
replica_checkpoint_period
</code>
sets the
maximum time (in milliseconds) that is allowed to pass
before a checkpoint operation is called to update the status
of a multithreaded replica as shown by
<a class="link" href="show-replica-status.html" title="15.7.7.35 SHOW REPLICA STATUS Statement">
<code class="literal">
SHOW REPLICA STATUS
</code>
</a>
. Setting
this variable has no effect on replicas for which
multithreading is not enabled. Setting this variable takes
effect for all replication channels immediately, including
running channels.
</p>
<p>
This variable works in combination with the
<a class="link" href="replication-options-replica.html#sysvar_replica_checkpoint_group">
<code class="literal">
replica_checkpoint_group
</code>
</a>
system variable in such a way that, when either limit is
exceeded, the checkpoint is executed and the counters
tracking both the number of transactions and the time
elapsed since the last checkpoint are reset.
</p>
<p>
The minimum allowed value for this variable is 1, unless the
server was built using
<a class="link" href="source-configuration-options.html#option_cmake_with_debug">
<code class="option">
-DWITH_DEBUG
</code>
</a>
, in which case
the minimum value is 0. Regardless of how the server was
built, the default value is 300 milliseconds, and the
maximum possible value is 4294967295 milliseconds
(approximately 49.7 days).
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_replica_compressed_protocol">
</a>
<a class="link" href="replication-options-replica.html#sysvar_replica_compressed_protocol">
<code class="literal">
replica_compressed_protocol
</code>
</a>
</p>
<a class="indexterm" name="idm46045142811440">
</a>
<a class="indexterm" name="idm46045142810336">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for replica_compressed_protocol">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--replica-compressed-protocol[={OFF|ON}]
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_replica_compressed_protocol">
replica_compressed_protocol
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Boolean
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
OFF
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
<a class="link" href="replication-options-replica.html#sysvar_replica_compressed_protocol">
<code class="literal">
replica_compressed_protocol
</code>
</a>
specifies whether to use compression of the source/replica
connection protocol if both source and replica support it.
If this variable is disabled (the default), connections are
uncompressed. Changes to this variable take effect on
subsequent connection attempts; this includes after issuing
a
<a class="link" href="start-replica.html" title="15.4.2.4 START REPLICA Statement">
<code class="literal">
START REPLICA
</code>
</a>
statement, as
well as reconnections made by a running replication I/O
(receiver) thread.
</p>
<p>
Binary log transaction compression, enabled by the
<a class="link" href="replication-options-binary-log.html#sysvar_binlog_transaction_compression">
<code class="literal">
binlog_transaction_compression
</code>
</a>
system variable, can also be used to save bandwidth. If you
use binary log transaction compression in combination with
protocol compression, protocol compression has less
opportunity to act on the data, but can still compress
headers and those events and transaction payloads that are
uncompressed. For more information on binary log transaction
compression, see
<a class="xref" href="binary-log-transaction-compression.html" title="7.4.4.5 Binary Log Transaction Compression">
Section 7.4.4.5, “Binary Log Transaction Compression”
</a>
.
</p>
<p>
If
<a class="link" href="replication-options-replica.html#sysvar_replica_compressed_protocol">
<code class="literal">
replica_compressed_protocol
</code>
</a>
is enabled, it takes precedence over any
<code class="literal">
SOURCE_COMPRESSION_ALGORITHMS
</code>
option
specified for the
<a class="link" href="change-replication-source-to.html" title="15.4.2.2 CHANGE REPLICATION SOURCE TO Statement">
<code class="literal">
CHANGE REPLICATION
SOURCE TO
</code>
</a>
statement. In this case, connections to
the source use
<code class="literal">
zlib
</code>
compression if both
the source and replica support that algorithm. If
<a class="link" href="replication-options-replica.html#sysvar_replica_compressed_protocol">
<code class="literal">
replica_compressed_protocol
</code>
</a>
is disabled, the value of
<code class="literal">
SOURCE_COMPRESSION_ALGORITHMS
</code>
applies.
For more information, see
<a class="xref" href="connection-compression-control.html" title="6.2.8 Connection Compression Control">
Section 6.2.8, “Connection Compression Control”
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_replica_exec_mode">
</a>
<a class="link" href="replication-options-replica.html#sysvar_replica_exec_mode">
<code class="literal">
replica_exec_mode
</code>
</a>
</p>
<a class="indexterm" name="idm46045142772464">
</a>
<a class="indexterm" name="idm46045142771424">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for replica_exec_mode">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--replica-exec-mode=mode
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_replica_exec_mode">
replica_exec_mode
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Enumeration
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<p class="valid-value">
<code class="literal">
IDEMPOTENT
</code>
(NDB)
</p>
<p class="valid-value">
<code class="literal">
STRICT
</code>
(Other)
</p>
</td>
</tr>
<tr>
<th>
Valid Values
</th>
<td>
<p class="valid-value">
<code class="literal">
STRICT
</code>
</p>
<p class="valid-value">
<code class="literal">
IDEMPOTENT
</code>
</p>
</td>
</tr>
</tbody>
</table>
</div>
<p>
<a class="link" href="replication-options-replica.html#sysvar_replica_exec_mode">
<code class="literal">
replica_exec_mode
</code>
</a>
controls
how a replication thread resolves conflicts and errors
during replication.
<code class="literal">
IDEMPOTENT
</code>
mode
causes suppression of duplicate-key and no-key-found errors;
<code class="literal">
STRICT
</code>
means no such suppression takes
place.
</p>
<p>
<code class="literal">
IDEMPOTENT
</code>
mode is intended for use in
multi-source replication, circular replication, and some
other special replication scenarios for NDB Cluster
Replication. (See
<a class="xref" href="mysql-cluster-replication-multi-source.html" title="25.7.10 NDB Cluster Replication: Bidirectional and Circular Replication">
Section 25.7.10, “NDB Cluster Replication: Bidirectional and Circular Replication”
</a>
,
and
<a class="xref" href="mysql-cluster-replication-conflict-resolution.html" title="25.7.12 NDB Cluster Replication Conflict Resolution">
Section 25.7.12, “NDB Cluster Replication Conflict Resolution”
</a>
,
for more information.) NDB Cluster ignores any value
explicitly set for
<a class="link" href="replication-options-replica.html#sysvar_replica_exec_mode">
<code class="literal">
replica_exec_mode
</code>
</a>
, and
always treats it as
<code class="literal">
IDEMPOTENT
</code>
.
</p>
<p>
In MySQL Server 8.4,
<code class="literal">
STRICT
</code>
mode is the default value.
</p>
<p>
Setting this variable takes immediate effect for all
replication channels, including running channels.
</p>
<p>
For storage engines other than
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDB
</code>
</a>
,
<span class="emphasis">
<em>
<code class="literal">
IDEMPOTENT
</code>
mode should be used
only when you are absolutely sure that duplicate-key errors
and key-not-found errors can safely be ignored
</em>
</span>
.
It is meant to be used in fail-over scenarios for NDB
Cluster where multi-source replication or circular
replication is employed, and is not recommended for use in
other cases.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_replica_load_tmpdir">
</a>
<a class="link" href="replication-options-replica.html#sysvar_replica_load_tmpdir">
<code class="literal">
replica_load_tmpdir
</code>
</a>
</p>
<a class="indexterm" name="idm46045142728560">
</a>
<a class="indexterm" name="idm46045142727520">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for replica_load_tmpdir">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--replica-load-tmpdir=dir_name
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_replica_load_tmpdir">
replica_load_tmpdir
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
No
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Directory name
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
Value of --tmpdir
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
<a class="link" href="replication-options-replica.html#sysvar_replica_load_tmpdir">
<code class="literal">
replica_load_tmpdir
</code>
</a>
specifies the name of the directory where the replica
creates temporary files. Setting this variable takes effect
for all replication channels immediately, including running
channels. The variable value is by default equal to the
value of the
<a class="link" href="server-system-variables.html#sysvar_tmpdir">
<code class="literal">
tmpdir
</code>
</a>
system
variable, or the default that applies when that system
variable is not specified.
</p>
<p>
When the replication SQL thread replicates a
<a class="link" href="load-data.html" title="15.2.9 LOAD DATA Statement">
<code class="literal">
LOAD DATA
</code>
</a>
statement, it
extracts the file to be loaded from the relay log into
temporary files, and then loads these into the table. If the
file loaded on the source is huge, the temporary files on
the replica are huge, too. Therefore, it might be advisable
to use this option to tell the replica to put temporary
files in a directory located in some file system that has a
lot of available space. In that case, the relay logs are
huge as well, so you might also want to set the
<a class="link" href="replication-options-replica.html#sysvar_relay_log">
<code class="literal">
relay_log
</code>
</a>
system variable
to place the relay logs in that file system.
</p>
<p>
The directory specified by this option should be located in
a disk-based file system (not a memory-based file system) so
that the temporary files used to replicate
<a class="link" href="load-data.html" title="15.2.9 LOAD DATA Statement">
<code class="literal">
LOAD DATA
</code>
</a>
statements can
survive machine restarts. The directory also should not be
one that is cleared by the operating system during the
system startup process. However, replication can now
continue after a restart if the temporary files have been
removed.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_replica_max_allowed_packet">
</a>
<a class="link" href="replication-options-replica.html#sysvar_replica_max_allowed_packet">
<code class="literal">
replica_max_allowed_packet
</code>
</a>
</p>
<a class="indexterm" name="idm46045142694464">
</a>
<a class="indexterm" name="idm46045142693360">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for replica_max_allowed_packet">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--replica-max-allowed-packet=#
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_replica_max_allowed_packet">
replica_max_allowed_packet
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Integer
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
1073741824
</code>
</td>
</tr>
<tr>
<th>
Minimum Value
</th>
<td>
<code class="literal">
1024
</code>
</td>
</tr>
<tr>
<th>
Maximum Value
</th>
<td>
<code class="literal">
1073741824
</code>
</td>
</tr>
<tr>
<th>
Unit
</th>
<td>
bytes
</td>
</tr>
<tr>
<th>
<a class="link" href="server-system-variables.html#system-variables-block-size" title="Note">
Block Size
</a>
</th>
<td>
<code class="literal">
1024
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
<a class="link" href="replication-options-replica.html#sysvar_replica_max_allowed_packet">
<code class="literal">
replica_max_allowed_packet
</code>
</a>
sets the maximum packet size in bytes that the replication
SQL (applier)and I/O (receiver) threads can handle. Setting
this variable takes effect for all replication channels
immediately, including running channels. It is possible for
a source to write binary log events longer than its
<a class="link" href="server-system-variables.html#sysvar_max_allowed_packet">
<code class="literal">
max_allowed_packet
</code>
</a>
setting
once the event header is added. The setting for
<a class="link" href="replication-options-replica.html#sysvar_replica_max_allowed_packet">
<code class="literal">
replica_max_allowed_packet
</code>
</a>
must be larger than the
<a class="link" href="server-system-variables.html#sysvar_max_allowed_packet">
<code class="literal">
max_allowed_packet
</code>
</a>
setting
on the source, so that large updates using row-based
replication do not cause replication to fail.
</p>
<p>
This global variable always has a value that is a positive
integer multiple of 1024; if you set it to some value that
is not, the value is rounded down to the next highest
multiple of 1024 for it is stored or used; setting
<code class="literal">
replica_max_allowed_packet
</code>
to 0 causes
1024 to be used. (A truncation warning is issued in all such
cases.) The default and maximum value is 1073741824 (1 GB);
the minimum is 1024.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_replica_net_timeout">
</a>
<a class="link" href="replication-options-replica.html#sysvar_replica_net_timeout">
<code class="literal">
replica_net_timeout
</code>
</a>
</p>
<a class="indexterm" name="idm46045142651600">
</a>
<a class="indexterm" name="idm46045142650560">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for replica_net_timeout">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--replica-net-timeout=#
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_replica_net_timeout">
replica_net_timeout
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Integer
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
60
</code>
</td>
</tr>
<tr>
<th>
Minimum Value
</th>
<td>
<code class="literal">
1
</code>
</td>
</tr>
<tr>
<th>
Maximum Value
</th>
<td>
<code class="literal">
31536000
</code>
</td>
</tr>
<tr>
<th>
Unit
</th>
<td>
seconds
</td>
</tr>
</tbody>
</table>
</div>
<p>
<a class="link" href="replication-options-replica.html#sysvar_replica_net_timeout">
<code class="literal">
replica_net_timeout
</code>
</a>
specifies the number of seconds to wait for more data or a
heartbeat signal from the source before the replica
considers the connection broken, aborts the read, and tries
to reconnect. Setting this variable has no immediate effect.
The state of the variable applies on all subsequent
<a class="link" href="start-replica.html" title="15.4.2.4 START REPLICA Statement">
<code class="literal">
START REPLICA
</code>
</a>
commands.
</p>
<p>
The default value is 60 seconds (one minute). The first
retry occurs immediately after the timeout. The interval
between retries is controlled by the
<code class="literal">
SOURCE_CONNECT_RETRY
</code>
option for the
<a class="link" href="change-replication-source-to.html" title="15.4.2.2 CHANGE REPLICATION SOURCE TO Statement">
<code class="literal">
CHANGE REPLICATION SOURCE TO
</code>
</a>
statement, and the number of reconnection attempts is
limited by the
<code class="literal">
SOURCE_RETRY_COUNT
</code>
option.
</p>
<p>
The heartbeat interval, which stops the connection timeout
occurring in the absence of data if the connection is still
good, is controlled by the
<code class="literal">
SOURCE_HEARTBEAT_PERIOD
</code>
option for the
<a class="link" href="change-replication-source-to.html" title="15.4.2.2 CHANGE REPLICATION SOURCE TO Statement">
<code class="literal">
CHANGE REPLICATION SOURCE TO
</code>
</a>
statement. The heartbeat interval defaults to half the value
of
<a class="link" href="replication-options-replica.html#sysvar_replica_net_timeout">
<code class="literal">
replica_net_timeout
</code>
</a>
, and
it is recorded in the replica's connection metadata
repository and shown in the
<a class="link" href="performance-schema-replication-connection-configuration-table.html" title="29.12.11.11 The replication_connection_configuration Table">
<code class="literal">
replication_connection_configuration
</code>
</a>
Performance Schema table. Note that a change to the value or
default setting of
<a class="link" href="replication-options-replica.html#sysvar_replica_net_timeout">
<code class="literal">
replica_net_timeout
</code>
</a>
does
not automatically change the heartbeat interval, whether
that has been set explicitly or is using a previously
calculated default. If the connection timeout is changed,
you must also issue
<a class="link" href="change-replication-source-to.html" title="15.4.2.2 CHANGE REPLICATION SOURCE TO Statement">
<code class="literal">
CHANGE REPLICATION
SOURCE TO
</code>
</a>
to adjust the heartbeat interval to an
appropriate value so that it occurs before the connection
timeout.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_replica_parallel_type">
</a>
<a class="link" href="replication-options-replica.html#sysvar_replica_parallel_type">
<code class="literal">
replica_parallel_type
</code>
</a>
</p>
<a class="indexterm" name="idm46045142604400">
</a>
<a class="indexterm" name="idm46045142603360">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for replica_parallel_type">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--replica-parallel-type=value
</code>
</td>
</tr>
<tr>
<th>
Deprecated
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_replica_parallel_type">
replica_parallel_type
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Enumeration
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
LOGICAL_CLOCK
</code>
</td>
</tr>
<tr>
<th>
Valid Values
</th>
<td>
<p class="valid-value">
<code class="literal">
DATABASE
</code>
</p>
<p class="valid-value">
<code class="literal">
LOGICAL_CLOCK
</code>
</p>
</td>
</tr>
</tbody>
</table>
</div>
<p>
For multithreaded replicas (replicas on which
<a class="link" href="replication-options-replica.html#sysvar_replica_parallel_workers">
<code class="literal">
replica_parallel_workers
</code>
</a>
is
set to a value greater than 0),
<a class="link" href="replication-options-replica.html#sysvar_replica_parallel_type">
<code class="literal">
replica_parallel_type
</code>
</a>
specifies the policy used to decide which transactions are
allowed to execute in parallel on the replica. The variable
has no effect on replicas for which multithreading is not
enabled. The possible values are:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<p>
<code class="literal">
LOGICAL_CLOCK
</code>
: Transactions are
applied in parallel on the replica, based on timestamps
which the replication source writes to the binary log.
Dependencies between transactions are tracked based on
their timestamps to provide additional parallelization
where possible.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
DATABASE
</code>
: Transactions that update
different databases are applied in parallel. This value
is only appropriate if data is partitioned into multiple
databases which are being updated independently and
concurrently on the source. There must be no
cross-database constraints, as such constraints may be
violated on the replica.
</p>
</li>
</ul>
</div>
<p>
When
<a class="link" href="replication-options-replica.html#sysvar_replica_preserve_commit_order">
<code class="literal">
replica_preserve_commit_order
</code>
</a>
is enabled, you must use
<code class="literal">
LOGICAL_CLOCK
</code>
.
Multithreading is enabled by default for replica servers
(
<a class="link" href="replication-options-replica.html#sysvar_replica_parallel_workers">
<code class="literal">
replica_parallel_workers=4
</code>
</a>
by default), and
<code class="literal">
LOGICAL_CLOCK
</code>
is the
default.
(
<a class="link" href="replication-options-replica.html#sysvar_replica_preserve_commit_order">
<code class="literal">
replica_preserve_commit_order
</code>
</a>
is also enabled by default.)
</p>
<p>
When the replication topology uses multiple levels of
replicas,
<code class="literal">
LOGICAL_CLOCK
</code>
may achieve less
parallelization for each level the replica is away from the
source.
</p>
<p>
When binary log transaction compression is enabled using the
<a class="link" href="replication-options-binary-log.html#sysvar_binlog_transaction_compression">
<code class="literal">
binlog_transaction_compression
</code>
</a>
system variable, if
<a class="link" href="replication-options-replica.html#sysvar_replica_parallel_type">
<code class="literal">
replica_parallel_type
</code>
</a>
is
set to
<code class="literal">
DATABASE
</code>
, all the databases
affected by the transaction are mapped before the
transaction is scheduled. The use of binary log transaction
compression with the
<code class="literal">
DATABASE
</code>
policy can
reduce parallelism compared to uncompressed transactions,
which are mapped and scheduled for each event.
</p>
<p>
<code class="literal">
replica_parallel_type
</code>
is deprecated, as
is support for parallelization of transactions using
database partitioning. Expect support for these to be
removed in a future release, and for
<code class="literal">
LOGICAL_CLOCK
</code>
to be used exclusively
thereafter.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_replica_parallel_workers">
</a>
<a class="link" href="replication-options-replica.html#sysvar_replica_parallel_workers">
<code class="literal">
replica_parallel_workers
</code>
</a>
</p>
<a class="indexterm" name="idm46045142552048">
</a>
<a class="indexterm" name="idm46045142550944">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for replica_parallel_workers">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--replica-parallel-workers=#
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_replica_parallel_workers">
replica_parallel_workers
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Integer
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
4
</code>
</td>
</tr>
<tr>
<th>
Minimum Value
</th>
<td>
<code class="literal">
0
</code>
</td>
</tr>
<tr>
<th>
Maximum Value
</th>
<td>
<code class="literal">
1024
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
<code class="literal">
replica_parallel_workers
</code>
enables
multithreading on the replica and sets the number of applier
threads for executing replication transactions in parallel.
When the value is greater than or equal to 1, the replica
uses the specified number of worker threads to execute
transactions, plus a coordinator thread that reads
transactions from the relay log and schedules them to
workers. When the value is 0, there is only one thread that
reads and applies transactions sequentially. If you are
using multiple replication channels, the value of this
variable applies to the threads used by each channel.
</p>
<p>
The default value is 4, which means that replicas are
multithreaded by default.
</p>
<p>
Setting this variable to 0 is deprecated, raises a warning,
and is subject to removal in a future MySQL release. For a
single worker, set
<code class="literal">
replica_parallel_workers
</code>
to 1 instead.
</p>
<p>
When
<a class="link" href="replication-options-replica.html#sysvar_replica_preserve_commit_order">
<code class="literal">
replica_preserve_commit_order
</code>
</a>
is
<code class="literal">
ON
</code>
(the default), transactions on a
replica are externalized on the replica in the same order as
they appear in the replica's relay log. The way in
which transactions are distributed among applier threads is
determined by
<a class="link" href="replication-options-replica.html#sysvar_replica_parallel_type">
<code class="literal">
replica_parallel_type
</code>
</a>
.
These system variables also have appropriate defaults for
multithreading.
</p>
<p>
To disable parallel execution, set
<code class="literal">
replica_parallel_workers
</code>
to 1, in which
case the replica uses one coordinator thread which reads
transactions, and one worker thread which applies them,
which means that transactions are applied sequentially. When
<code class="literal">
replica_parallel_workers
</code>
is equal to 1,
the
<a class="link" href="replication-options-replica.html#sysvar_replica_parallel_type">
<code class="literal">
replica_parallel_type
</code>
</a>
and
<a class="link" href="replication-options-replica.html#sysvar_replica_preserve_commit_order">
<code class="literal">
replica_preserve_commit_order
</code>
</a>
system variables have no effect and are ignored. If
<code class="literal">
replica_parallel_workers
</code>
is equal to 0
while the
<a class="link" href="change-replication-source-to.html" title="15.4.2.2 CHANGE REPLICATION SOURCE TO Statement">
<code class="literal">
CHANGE REPLICATION SOURCE
TO
</code>
</a>
option
<a class="link" href="change-replication-source-to.html#crs-opt-gtid_only">
<code class="literal">
GTID_ONLY
</code>
</a>
is enabled, the
replica has one coordinator thread and one worker thread,
exactly as if
<code class="literal">
replica_parallel_workers
</code>
had been set to 1. With one parallel worker, the
<a class="link" href="replication-options-replica.html#sysvar_replica_preserve_commit_order">
<code class="literal">
replica_preserve_commit_order
</code>
</a>
system variable also has no effect.
</p>
<p>
Setting
<a class="link" href="replication-options-replica.html#sysvar_replica_parallel_workers">
<code class="literal">
replica_parallel_workers
</code>
</a>
has no immediate effect but rather applies to all subsequent
<a class="link" href="start-replica.html" title="15.4.2.4 START REPLICA Statement">
<code class="literal">
START REPLICA
</code>
</a>
statements.
</p>
<p>
Multithreaded replicas are also supported by NDB Cluster
8.4. See
<a class="xref" href="mysql-cluster-replication-mta.html" title="25.7.11 NDB Cluster Replication Using the Multithreaded Applier">
Section 25.7.11, “NDB Cluster Replication Using the Multithreaded Applier”
</a>
, for more
information.
</p>
<p>
Increasing the number of workers improves the potential for
parallelism. Typically, this improves performance up to a
certain point, beyond which increasing the number of workers
reduces performance due to concurrency effects such as lock
contention. The ideal number depends on both hardware and
workload; it can be difficult to predict and typically has
to be found by testing. Tables without primary keys, which
always harm performance, may have even greater negative
performance impact on replicas having
<code class="literal">
replica_parallel_workers
</code>
> 1; so make
sure that all tables have primary keys before enabling this
option.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_replica_pending_jobs_size_max">
</a>
<a class="link" href="replication-options-replica.html#sysvar_replica_pending_jobs_size_max">
<code class="literal">
replica_pending_jobs_size_max
</code>
</a>
</p>
<a class="indexterm" name="idm46045142497776">
</a>
<a class="indexterm" name="idm46045142496272">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for replica_pending_jobs_size_max">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--replica-pending-jobs-size-max=#
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_replica_pending_jobs_size_max">
replica_pending_jobs_size_max
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Integer
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
128M
</code>
</td>
</tr>
<tr>
<th>
Minimum Value
</th>
<td>
<code class="literal">
1024
</code>
</td>
</tr>
<tr>
<th>
Maximum Value
</th>
<td>
<code class="literal">
16EiB
</code>
</td>
</tr>
<tr>
<th>
Unit
</th>
<td>
bytes
</td>
</tr>
<tr>
<th>
<a class="link" href="server-system-variables.html#system-variables-block-size" title="Note">
Block Size
</a>
</th>
<td>
<code class="literal">
1024
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
For multithreaded replicas, this variable sets the maximum
amount of memory (in bytes) available to applier queues
holding events not yet applied. Setting this variable has no
effect on replicas for which multithreading is not enabled.
Setting this variable has no immediate effect. The state of
the variable applies on all subsequent
<a class="link" href="start-replica.html" title="15.4.2.4 START REPLICA Statement">
<code class="literal">
START REPLICA
</code>
</a>
commands.
</p>
<p>
The minimum possible value for this variable is 1024 bytes;
the default is 128MB. The maximum possible value is
18446744073709551615 (16 exbibytes). Values that are not
exact multiples of 1024 bytes are rounded down to the next
lower multiple of 1024 bytes prior to being stored.
</p>
<p>
The value of this variable is a soft limit and can be set to
match the normal workload. If an unusually large event
exceeds this size, the transaction is held until all the
worker threads have empty queues, and then processed. All
subsequent transactions are held until the large transaction
has been completed.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_replica_preserve_commit_order">
</a>
<a class="link" href="replication-options-replica.html#sysvar_replica_preserve_commit_order">
<code class="literal">
replica_preserve_commit_order
</code>
</a>
</p>
<a class="indexterm" name="idm46045142458576">
</a>
<a class="indexterm" name="idm46045142457072">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for replica_preserve_commit_order">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--replica-preserve-commit-order[={OFF|ON}]
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_replica_preserve_commit_order">
replica_preserve_commit_order
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Boolean
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
ON
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
For multithreaded replicas (replicas on which
<a class="link" href="replication-options-replica.html#sysvar_replica_parallel_workers">
<code class="literal">
replica_parallel_workers
</code>
</a>
is
set to a value greater than 0), setting
<a class="link" href="replication-options-replica.html#sysvar_replica_preserve_commit_order">
<code class="literal">
replica_preserve_commit_order=ON
</code>
</a>
ensures that transactions are executed and committed on the
replica in the same order as they appear in the
replica's relay log. This prevents gaps in the sequence
of transactions that have been executed from the replica's
relay log, and preserves the same transaction history on the
replica as on the source (with the limitations listed
below). This variable has no effect on replicas for which
multithreading is not enabled.
</p>
<p>
Multithreading is enabled by default in MySQL
8.4 for replica servers
(
<a class="link" href="replication-options-replica.html#sysvar_replica_parallel_workers">
<code class="literal">
replica_parallel_workers=4
</code>
</a>
by default), so
<a class="link" href="replication-options-replica.html#sysvar_replica_preserve_commit_order">
<code class="literal">
replica_preserve_commit_order=ON
</code>
</a>
is the default, and the setting
<a class="link" href="replication-options-replica.html#sysvar_replica_parallel_type">
<code class="literal">
replica_parallel_type=LOGICAL_CLOCK
</code>
</a>
is also the default. In addition, the setting for
<a class="link" href="replication-options-replica.html#sysvar_replica_preserve_commit_order">
<code class="literal">
replica_preserve_commit_order
</code>
</a>
is ignored if
<a class="link" href="replication-options-replica.html#sysvar_replica_parallel_workers">
<code class="literal">
replica_parallel_workers
</code>
</a>
is
set to 1, because in that situation the order of
transactions is preserved anyway.
</p>
<p>
Binary logging and replica update logging are not required
on the replica to set
<a class="link" href="replication-options-replica.html#sysvar_replica_preserve_commit_order">
<code class="literal">
replica_preserve_commit_order=ON
</code>
</a>
,
and can be disabled if wanted. Setting
<a class="link" href="replication-options-replica.html#sysvar_replica_preserve_commit_order">
<code class="literal">
replica_preserve_commit_order=ON
</code>
</a>
requires that
<a class="link" href="replication-options-replica.html#sysvar_replica_parallel_type">
<code class="literal">
replica_parallel_type
</code>
</a>
is
set to
<code class="literal">
LOGICAL_CLOCK
</code>
, the default in
MySQL 8.4. Before changing the value of
<a class="link" href="replication-options-replica.html#sysvar_replica_preserve_commit_order">
<code class="literal">
replica_preserve_commit_order
</code>
</a>
and
<a class="link" href="replication-options-replica.html#sysvar_replica_parallel_type">
<code class="literal">
replica_parallel_type
</code>
</a>
,
the replication SQL thread (for all replication channels if
you are using multiple replication channels) must be
stopped.
</p>
<p>
When
<a class="link" href="replication-options-replica.html#sysvar_replica_preserve_commit_order">
<code class="literal">
replica_preserve_commit_order=OFF
</code>
</a>
is set, the transactions that a multithreaded replica
applies in parallel may commit out of order. Therefore,
checking for the most recently executed transaction does not
guarantee that all previous transactions from the source
have been executed on the replica. There is a chance of gaps
in the sequence of transactions that have been executed from
the replica's relay log. This has implications for logging
and recovery when using a multithreaded replica. See
<a class="xref" href="replication-features-transaction-inconsistencies.html" title="19.5.1.34 Replication and Transaction Inconsistencies">
Section 19.5.1.34, “Replication and Transaction Inconsistencies”
</a>
for more information.
</p>
<p>
When
<a class="link" href="replication-options-replica.html#sysvar_replica_preserve_commit_order">
<code class="literal">
replica_preserve_commit_order=ON
</code>
</a>
is set, the executing worker thread waits until all previous
transactions are committed before committing. While a given
thread is waiting for other worker threads to commit their
transactions, it reports its status as
<code class="literal">
Waiting for
preceding transaction to commit
</code>
. With this mode, a
multithreaded replica never enters a state that the source
was not in. This supports the use of replication for read
scale-out. See
<a class="xref" href="replication-solutions-scaleout.html" title="19.4.5 Using Replication for Scale-Out">
Section 19.4.5, “Using Replication for Scale-Out”
</a>
.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<p>
<a class="link" href="replication-options-replica.html#sysvar_replica_preserve_commit_order">
<code class="literal">
replica_preserve_commit_order=ON
</code>
</a>
does not prevent source binary log position lag, where
<code class="literal">
Exec_master_log_pos
</code>
is behind the
position up to which transactions have been executed.
See
<a class="xref" href="replication-features-transaction-inconsistencies.html" title="19.5.1.34 Replication and Transaction Inconsistencies">
Section 19.5.1.34, “Replication and Transaction Inconsistencies”
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a class="link" href="replication-options-replica.html#sysvar_replica_preserve_commit_order">
<code class="literal">
replica_preserve_commit_order=ON
</code>
</a>
does not preserve the commit order and transaction
history if the replica uses filters on its binary log,
such as
<a class="link" href="replication-options-binary-log.html#option_mysqld_binlog-do-db">
<code class="option">
--binlog-do-db
</code>
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a class="link" href="replication-options-replica.html#sysvar_replica_preserve_commit_order">
<code class="literal">
replica_preserve_commit_order=ON
</code>
</a>
does not preserve the order of non-transactional DML
updates. These might commit before transactions that
precede them in the relay log, which might result in
gaps in the sequence of transactions that have been
executed from the replica's relay log.
</p>
</li>
<li class="listitem">
<p>
A limitation to preserving the commit order on the
replica can occur if statement-based replication is in
use, and both transactional and non-transactional
storage engines participate in a non-XA transaction
that is rolled back on the source. Normally, non-XA
transactions that are rolled back on the source are
not replicated to the replica, but in this particular
situation, the transaction might be replicated to the
replica. If this does happen, a multithreaded replica
without binary logging does not handle the transaction
rollback, so the commit order on the replica diverges
from the relay log order of the transactions in that
case.
</p>
</li>
</ul>
</div>
</div>
</li>
<li class="listitem">
<p>
<a name="sysvar_replica_sql_verify_checksum">
</a>
<a class="link" href="replication-options-replica.html#sysvar_replica_sql_verify_checksum">
<code class="literal">
replica_sql_verify_checksum
</code>
</a>
</p>
<a class="indexterm" name="idm46045142396160">
</a>
<a class="indexterm" name="idm46045142395056">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for replica_sql_verify_checksum">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--replica-sql-verify-checksum[={OFF|ON}]
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_replica_sql_verify_checksum">
replica_sql_verify_checksum
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Boolean
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
ON
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
<a class="link" href="replication-options-replica.html#sysvar_replica_sql_verify_checksum">
<code class="literal">
replica_sql_verify_checksum
</code>
</a>
causes the replication SQL (applier) thread to verify data
using the checksums read from the relay log. In the event of
a mismatch, the replica stops with an error. Setting this
variable takes effect for all replication channels
immediately, including running channels.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
The replication I/O (receiver)thread always reads
checksums if possible when accepting events from over the
network.
</p>
</div>
</li>
<li class="listitem">
<p>
<a name="sysvar_replica_transaction_retries">
</a>
<a class="link" href="replication-options-replica.html#sysvar_replica_transaction_retries">
<code class="literal">
replica_transaction_retries
</code>
</a>
</p>
<a class="indexterm" name="idm46045142368000">
</a>
<a class="indexterm" name="idm46045142366896">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for replica_transaction_retries">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--replica-transaction-retries=#
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_replica_transaction_retries">
replica_transaction_retries
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Integer
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
10
</code>
</td>
</tr>
<tr>
<th>
Minimum Value
</th>
<td>
<code class="literal">
0
</code>
</td>
</tr>
<tr>
<th>
Maximum Value
</th>
<td>
<code class="literal">
18446744073709551615
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
<a class="link" href="replication-options-replica.html#sysvar_replica_transaction_retries">
<code class="literal">
replica_transaction_retries
</code>
</a>
sets the maximum number of times for replication SQL threads
on a single-threaded or multithreaded replica to
automatically retry failed transactions before stopping.
Setting this variable takes effect for all replication
channels immediately, including running channels. The
default value is 10. Setting the variable to 0 disables
automatic retrying of transactions.
</p>
<p>
If a replication SQL thread fails to execute a transaction
because of an
<a class="link" href="innodb-storage-engine.html" title="Chapter 17 The InnoDB Storage Engine">
<code class="literal">
InnoDB
</code>
</a>
deadlock
or because the transaction's execution time exceeded
<a class="link" href="innodb-storage-engine.html" title="Chapter 17 The InnoDB Storage Engine">
<code class="literal">
InnoDB
</code>
</a>
's
<a class="link" href="innodb-parameters.html#sysvar_innodb_lock_wait_timeout">
<code class="literal">
innodb_lock_wait_timeout
</code>
</a>
or
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDB
</code>
</a>
's
<a class="link" href="mysql-cluster-ndbd-definition.html#ndbparam-ndbd-transactiondeadlockdetectiontimeout">
<code class="literal">
TransactionDeadlockDetectionTimeout
</code>
</a>
or
<a class="link" href="mysql-cluster-ndbd-definition.html#ndbparam-ndbd-transactioninactivetimeout">
<code class="literal">
TransactionInactiveTimeout
</code>
</a>
,
it automatically retries
<a class="link" href="replication-options-replica.html#sysvar_replica_transaction_retries">
<code class="literal">
replica_transaction_retries
</code>
</a>
times before stopping with an error. Transactions with a
non-temporary error are not retried.
</p>
<p>
The Performance Schema table
<a class="link" href="performance-schema-replication-applier-status-table.html" title="29.12.11.5 The replication_applier_status Table">
<code class="literal">
replication_applier_status
</code>
</a>
shows the number of retries that took place on each
replication channel, in the
<code class="literal">
COUNT_TRANSACTIONS_RETRIES
</code>
column. The
Performance Schema table
<a class="link" href="performance-schema-replication-applier-status-by-worker-table.html" title="29.12.11.7 The replication_applier_status_by_worker Table">
<code class="literal">
replication_applier_status_by_worker
</code>
</a>
shows detailed information on transaction retries by
individual applier threads on a single-threaded or
multithreaded replica, and identifies the errors that caused
the last transaction and the transaction currently in
progress to be reattempted.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_replica_type_conversions">
</a>
<a class="link" href="replication-options-replica.html#sysvar_replica_type_conversions">
<code class="literal">
replica_type_conversions
</code>
</a>
</p>
<a class="indexterm" name="idm46045142321424">
</a>
<a class="indexterm" name="idm46045142320320">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for replica_type_conversions">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--replica-type-conversions=set
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_replica_type_conversions">
replica_type_conversions
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Set
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
</code>
</td>
</tr>
<tr>
<th>
Valid Values
</th>
<td>
<p class="valid-value">
<code class="literal">
ALL_LOSSY
</code>
</p>
<p class="valid-value">
<code class="literal">
ALL_NON_LOSSY
</code>
</p>
<p class="valid-value">
<code class="literal">
ALL_SIGNED
</code>
</p>
<p class="valid-value">
<code class="literal">
ALL_UNSIGNED
</code>
</p>
</td>
</tr>
</tbody>
</table>
</div>
<p>
<a class="link" href="replication-options-replica.html#sysvar_replica_type_conversions">
<code class="literal">
replica_type_conversions
</code>
</a>
controls the type conversion mode in effect on the replica
when using row-based replication. Its value is a
comma-delimited set of zero or more elements from the list:
<code class="literal">
ALL_LOSSY
</code>
,
<code class="literal">
ALL_NON_LOSSY
</code>
,
<code class="literal">
ALL_SIGNED
</code>
,
<code class="literal">
ALL_UNSIGNED
</code>
. Set this variable to an
empty string to disallow type conversions between the source
and the replica. Setting this variable takes effect for all
replication channels immediately, including running
channels.
</p>
<p>
For additional information on type conversion modes
applicable to attribute promotion and demotion in row-based
replication, see
<a class="xref" href="replication-features-differing-tables.html#replication-features-attribute-promotion" title="Row-based replication: attribute promotion and demotion">
Row-based replication: attribute promotion and demotion
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_replication_optimize_for_static_plugin_config">
</a>
<a class="link" href="replication-options-replica.html#sysvar_replication_optimize_for_static_plugin_config">
<code class="literal">
replication_optimize_for_static_plugin_config
</code>
</a>
</p>
<a class="indexterm" name="idm46045142284080">
</a>
<a class="indexterm" name="idm46045142283040">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for replication_optimize_for_static_plugin_config">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--replication-optimize-for-static-plugin-config[={OFF|ON}]
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_replication_optimize_for_static_plugin_config">
replication_optimize_for_static_plugin_config
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Boolean
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
OFF
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
Use shared locks, and avoid unnecessary lock acquisitions,
to improve performance for semisynchronous replication. This
setting and
<a class="link" href="replication-options-replica.html#sysvar_replication_sender_observe_commit_only">
<code class="literal">
replication_sender_observe_commit_only
</code>
</a>
help as the number of replicas increases, because contention
for locks can slow down performance. While this system
variable is enabled, the semisynchronous replication plugin
cannot be uninstalled, so you must disable the system
variable before the uninstall can complete.
</p>
<p>
This system variable can be enabled before or after
installing the semisynchronous replication plugin, and can
be enabled while replication is running. Semisynchronous
replication source servers can also get performance benefits
from enabling this system variable, because they use the
same locking mechanisms as the replicas.
</p>
<p>
<a class="link" href="replication-options-replica.html#sysvar_replication_optimize_for_static_plugin_config">
<code class="literal">
replication_optimize_for_static_plugin_config
</code>
</a>
can be enabled when Group Replication is in use on a server.
In that scenario, it might benefit performance when there is
contention for locks due to high workloads.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_replication_sender_observe_commit_only">
</a>
<a class="link" href="replication-options-replica.html#sysvar_replication_sender_observe_commit_only">
<code class="literal">
replication_sender_observe_commit_only
</code>
</a>
</p>
<a class="indexterm" name="idm46045142253760">
</a>
<a class="indexterm" name="idm46045142252720">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for replication_sender_observe_commit_only">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--replication-sender-observe-commit-only[={OFF|ON}]
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_replication_sender_observe_commit_only">
replication_sender_observe_commit_only
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Boolean
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
OFF
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
Limit callbacks to improve performance for semisynchronous
replication. This setting and
<a class="link" href="replication-options-replica.html#sysvar_replication_optimize_for_static_plugin_config">
<code class="literal">
replication_optimize_for_static_plugin_config
</code>
</a>
help as the number of replicas increases, because contention
for locks can slow down performance.
</p>
<p>
This system variable can be enabled before or after
installing the semisynchronous replication plugin, and can
be enabled while replication is running. Semisynchronous
replication source servers can also get performance benefits
from enabling this system variable, because they use the
same locking mechanisms as the replicas.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_report_host">
</a>
<a class="link" href="replication-options-replica.html#sysvar_report_host">
<code class="literal">
report_host
</code>
</a>
</p>
<a class="indexterm" name="idm46045142225808">
</a>
<a class="indexterm" name="idm46045142224720">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for report_host">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--report-host=host_name
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_report_host">
report_host
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
No
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
String
</td>
</tr>
</tbody>
</table>
</div>
<p>
The host name or IP address of the replica to be reported to
the source during replica registration. This value appears
in the output of
<a class="link" href="show-replicas.html" title="15.7.7.36 SHOW REPLICAS Statement">
<code class="literal">
SHOW
REPLICAS
</code>
</a>
on the source server. Leave the value
unset if you do not want the replica to register itself with
the source.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
It is not sufficient for the source to simply read the IP
address of the replica server from the TCP/IP socket after
the replica connects. Due to NAT and other routing issues,
that IP may not be valid for connecting to the replica
from the source or other hosts.
</p>
</div>
</li>
<li class="listitem">
<p>
<a name="sysvar_report_password">
</a>
<a class="link" href="replication-options-replica.html#sysvar_report_password">
<code class="literal">
report_password
</code>
</a>
</p>
<a class="indexterm" name="idm46045142200128">
</a>
<a class="indexterm" name="idm46045142199040">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for report_password">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--report-password=name
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_report_password">
report_password
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
No
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
String
</td>
</tr>
</tbody>
</table>
</div>
<p>
The account password of the replica to be reported to the
source during replica registration. This value appears in
the output of
<a class="link" href="show-replicas.html" title="15.7.7.36 SHOW REPLICAS Statement">
<code class="literal">
SHOW REPLICAS
</code>
</a>
on the source server if the source was started with
<a class="link" href="replication-options-source.html#option_mysqld_show-replica-auth-info">
<code class="option">
--show-replica-auth-info
</code>
</a>
.
</p>
<p>
Although the name of this variable might imply otherwise,
<a class="link" href="replication-options-replica.html#sysvar_report_password">
<code class="literal">
report_password
</code>
</a>
is not
connected to the MySQL user privilege system and so is not
necessarily (or even likely to be) the same as the password
for the MySQL replication user account.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_report_port">
</a>
<a class="link" href="replication-options-replica.html#sysvar_report_port">
<code class="literal">
report_port
</code>
</a>
</p>
<a class="indexterm" name="idm46045142172704">
</a>
<a class="indexterm" name="idm46045142171616">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for report_port">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--report-port=port_num
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_report_port">
report_port
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
No
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Integer
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
[slave_port]
</code>
</td>
</tr>
<tr>
<th>
Minimum Value
</th>
<td>
<code class="literal">
0
</code>
</td>
</tr>
<tr>
<th>
Maximum Value
</th>
<td>
<code class="literal">
65535
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
The TCP/IP port number for connecting to the replica, to be
reported to the source during replica registration. Set this
only if the replica is listening on a nondefault port or if
you have a special tunnel from the source or other clients
to the replica. If you are not sure, do not use this option.
</p>
<p>
The default value for this option is the port number
actually used by the replica. This is also the default value
displayed by
<a class="link" href="show-replicas.html" title="15.7.7.36 SHOW REPLICAS Statement">
<code class="literal">
SHOW REPLICAS
</code>
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_report_user">
</a>
<a class="link" href="replication-options-replica.html#sysvar_report_user">
<code class="literal">
report_user
</code>
</a>
</p>
<a class="indexterm" name="idm46045142140176">
</a>
<a class="indexterm" name="idm46045142139088">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for report_user">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--report-user=name
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_report_user">
report_user
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
No
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
String
</td>
</tr>
</tbody>
</table>
</div>
<p>
The account user name of the replica to be reported to the
source during replica registration. This value appears in
the output of
<a class="link" href="show-replicas.html" title="15.7.7.36 SHOW REPLICAS Statement">
<code class="literal">
SHOW REPLICAS
</code>
</a>
on the source server if the source was started with
<a class="link" href="replication-options-source.html#option_mysqld_show-replica-auth-info">
<code class="option">
--show-replica-auth-info
</code>
</a>
.
</p>
<p>
Although the name of this variable might imply otherwise,
<a class="link" href="replication-options-replica.html#sysvar_report_user">
<code class="literal">
report_user
</code>
</a>
is not
connected to the MySQL user privilege system and so is not
necessarily (or even likely to be) the same as the name of
the MySQL replication user account.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_rpl_read_size">
</a>
<a class="link" href="replication-options-replica.html#sysvar_rpl_read_size">
<code class="literal">
rpl_read_size
</code>
</a>
</p>
<a class="indexterm" name="idm46045142112800">
</a>
<a class="indexterm" name="idm46045142111312">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for rpl_read_size">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--rpl-read-size=#
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_rpl_read_size">
rpl_read_size
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Integer
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
8192
</code>
</td>
</tr>
<tr>
<th>
Minimum Value
</th>
<td>
<code class="literal">
8192
</code>
</td>
</tr>
<tr>
<th>
Maximum Value
</th>
<td>
<code class="literal">
4294959104
</code>
</td>
</tr>
<tr>
<th>
Unit
</th>
<td>
bytes
</td>
</tr>
<tr>
<th>
<a class="link" href="server-system-variables.html#system-variables-block-size" title="Note">
Block Size
</a>
</th>
<td>
<code class="literal">
8192
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
The
<a class="link" href="replication-options-replica.html#sysvar_rpl_read_size">
<code class="literal">
rpl_read_size
</code>
</a>
system
variable controls the minimum amount of data in bytes that
is read from the binary log files and relay log files. If
heavy disk I/O activity for these files is impeding
performance for the database, increasing the read size might
reduce file reads and I/O stalls when the file data is not
currently cached by the operating system.
</p>
<p>
The minimum and default value for
<a class="link" href="replication-options-replica.html#sysvar_rpl_read_size">
<code class="literal">
rpl_read_size
</code>
</a>
is 8192
bytes. The value must be a multiple of 4KB. Note that a
buffer the size of this value is allocated for each thread
that reads from the binary log and relay log files,
including dump threads on sources and coordinator threads on
replicas. Setting a large value might therefore have an
impact on memory consumption for servers.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_rpl_semi_sync_replica_enabled">
</a>
<a class="link" href="replication-options-replica.html#sysvar_rpl_semi_sync_replica_enabled">
<code class="literal">
rpl_semi_sync_replica_enabled
</code>
</a>
</p>
<a class="indexterm" name="idm46045142073536">
</a>
<a class="indexterm" name="idm46045142072432">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for rpl_semi_sync_replica_enabled">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--rpl-semi-sync-replica-enabled[={OFF|ON}]
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_rpl_semi_sync_replica_enabled">
rpl_semi_sync_replica_enabled
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Boolean
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
OFF
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
<a class="link" href="replication-options-replica.html#sysvar_rpl_semi_sync_replica_enabled">
<code class="literal">
rpl_semi_sync_replica_enabled
</code>
</a>
controls whether semisynchronous replication is enabled on
the replica server. To enable or disable the plugin, set
this variable to
<code class="literal">
ON
</code>
or
<code class="literal">
OFF
</code>
(or 1 or 0), respectively. The
default is
<code class="literal">
OFF
</code>
.
</p>
<p>
This variable is available only if the replica-side
semisynchronous replication plugin is installed.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_rpl_semi_sync_replica_trace_level">
</a>
<a class="link" href="replication-options-replica.html#sysvar_rpl_semi_sync_replica_trace_level">
<code class="literal">
rpl_semi_sync_replica_trace_level
</code>
</a>
</p>
<a class="indexterm" name="idm46045142043728">
</a>
<a class="indexterm" name="idm46045142042688">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for rpl_semi_sync_replica_trace_level">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--rpl-semi-sync-replica-trace-level=#
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_rpl_semi_sync_replica_trace_level">
rpl_semi_sync_replica_trace_level
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Integer
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
32
</code>
</td>
</tr>
<tr>
<th>
Minimum Value
</th>
<td>
<code class="literal">
0
</code>
</td>
</tr>
<tr>
<th>
Maximum Value
</th>
<td>
<code class="literal">
4294967295
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
<a class="link" href="replication-options-replica.html#sysvar_rpl_semi_sync_replica_trace_level">
<code class="literal">
rpl_semi_sync_replica_trace_level
</code>
</a>
controls the semisynchronous replication debug trace level
on the replica server. See
<a class="link" href="replication-options-source.html#sysvar_rpl_semi_sync_master_trace_level">
<code class="literal">
rpl_semi_sync_master_trace_level
</code>
</a>
for the permissible values.
</p>
<p>
This variable is available only if the replica-side
semisynchronous replication plugin is installed.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_rpl_semi_sync_slave_enabled">
</a>
<a class="link" href="replication-options-replica.html#sysvar_rpl_semi_sync_slave_enabled">
<code class="literal">
rpl_semi_sync_slave_enabled
</code>
</a>
</p>
<a class="indexterm" name="idm46045142009968">
</a>
<a class="indexterm" name="idm46045142008864">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for rpl_semi_sync_slave_enabled">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--rpl-semi-sync-slave-enabled[={OFF|ON}]
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_rpl_semi_sync_slave_enabled">
rpl_semi_sync_slave_enabled
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Boolean
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
OFF
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
Deprecated synonym for
<a class="link" href="replication-options-replica.html#sysvar_rpl_semi_sync_replica_enabled">
<code class="literal">
rpl_semi_sync_replica_enabled
</code>
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_rpl_semi_sync_slave_trace_level">
</a>
<a class="link" href="replication-options-replica.html#sysvar_rpl_semi_sync_slave_trace_level">
<code class="literal">
rpl_semi_sync_slave_trace_level
</code>
</a>
</p>
<a class="indexterm" name="idm46045141982960">
</a>
<a class="indexterm" name="idm46045141981856">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for rpl_semi_sync_slave_trace_level">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--rpl-semi-sync-slave-trace-level=#
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_rpl_semi_sync_slave_trace_level">
rpl_semi_sync_slave_trace_level
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Integer
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
32
</code>
</td>
</tr>
<tr>
<th>
Minimum Value
</th>
<td>
<code class="literal">
0
</code>
</td>
</tr>
<tr>
<th>
Maximum Value
</th>
<td>
<code class="literal">
4294967295
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
Deprecated synonym for
<a class="link" href="replication-options-replica.html#sysvar_rpl_semi_sync_replica_trace_level">
<code class="literal">
rpl_semi_sync_replica_trace_level
</code>
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_rpl_stop_replica_timeout">
</a>
<a class="link" href="replication-options-replica.html#sysvar_rpl_stop_replica_timeout">
<code class="literal">
rpl_stop_replica_timeout
</code>
</a>
</p>
<a class="indexterm" name="idm46045141951136">
</a>
<a class="indexterm" name="idm46045141949632">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for rpl_stop_replica_timeout">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--rpl-stop-replica-timeout=#
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_rpl_stop_replica_timeout">
rpl_stop_replica_timeout
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Integer
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
31536000
</code>
</td>
</tr>
<tr>
<th>
Minimum Value
</th>
<td>
<code class="literal">
2
</code>
</td>
</tr>
<tr>
<th>
Maximum Value
</th>
<td>
<code class="literal">
31536000
</code>
</td>
</tr>
<tr>
<th>
Unit
</th>
<td>
seconds
</td>
</tr>
</tbody>
</table>
</div>
<p>
You can control the length of time (in seconds) that
<a class="link" href="stop-replica.html" title="15.4.2.5 STOP REPLICA Statement">
<code class="literal">
STOP REPLICA
</code>
</a>
waits before
timing out by setting this variable. This can be used to
avoid deadlocks between
<a class="link" href="stop-replica.html" title="15.4.2.5 STOP REPLICA Statement">
<code class="literal">
STOP
REPLICA
</code>
</a>
and other SQL statements using different
client connections to the replica.
</p>
<p>
The maximum and default value of
<code class="literal">
rpl_stop_replica_timeout
</code>
is 31536000
seconds (1 year). The minimum is 2 seconds. Changes to this
variable take effect for subsequent
<a class="link" href="stop-replica.html" title="15.4.2.5 STOP REPLICA Statement">
<code class="literal">
STOP REPLICA
</code>
</a>
statements.
</p>
<p>
This variable affects only the client that issues a
<a class="link" href="stop-replica.html" title="15.4.2.5 STOP REPLICA Statement">
<code class="literal">
STOP REPLICA
</code>
</a>
statement. When
the timeout is reached, the issuing client returns an error
message stating that the command execution is incomplete.
The client then stops waiting for the replication I/O
(receiver)and SQL (applier) threads to stop, but the
replication threads continue to try to stop, and the
<a class="link" href="stop-replica.html" title="15.4.2.5 STOP REPLICA Statement">
<code class="literal">
STOP REPLICA
</code>
</a>
statement
remains in effect. Once the replication threads are no
longer busy, the
<a class="link" href="stop-replica.html" title="15.4.2.5 STOP REPLICA Statement">
<code class="literal">
STOP REPLICA
</code>
</a>
statement is executed and the replica stops.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_rpl_stop_slave_timeout">
</a>
<a class="link" href="replication-options-replica.html#sysvar_rpl_stop_slave_timeout">
<code class="literal">
rpl_stop_slave_timeout
</code>
</a>
</p>
<a class="indexterm" name="idm46045141908608">
</a>
<a class="indexterm" name="idm46045141907120">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for rpl_stop_slave_timeout">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--rpl-stop-slave-timeout=#
</code>
</td>
</tr>
<tr>
<th>
Deprecated
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_rpl_stop_slave_timeout">
rpl_stop_slave_timeout
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Integer
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
31536000
</code>
</td>
</tr>
<tr>
<th>
Minimum Value
</th>
<td>
<code class="literal">
2
</code>
</td>
</tr>
<tr>
<th>
Maximum Value
</th>
<td>
<code class="literal">
31536000
</code>
</td>
</tr>
<tr>
<th>
Unit
</th>
<td>
seconds
</td>
</tr>
</tbody>
</table>
</div>
<p>
Deprecated synonym for
<a class="link" href="replication-options-replica.html#sysvar_rpl_stop_replica_timeout">
<code class="literal">
rpl_stop_replica_timeout
</code>
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_skip_replica_start">
</a>
<a class="link" href="replication-options-replica.html#sysvar_skip_replica_start">
<code class="literal">
skip_replica_start
</code>
</a>
</p>
<a class="indexterm" name="idm46045141872800">
</a>
<a class="indexterm" name="idm46045141871760">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for skip-replica-start">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--skip-replica-start[={OFF|ON}]
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_skip_replica_start">
skip_replica_start
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
No
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Boolean
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
OFF
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
<a class="link" href="replication-options-replica.html#sysvar_skip_replica_start">
<code class="literal">
skip_replica_start
</code>
</a>
tells
the replica server not to start the replication I/O
(receiver) and SQL (applier) threads when the server starts.
To start the threads later, use a
<a class="link" href="start-replica.html" title="15.4.2.4 START REPLICA Statement">
<code class="literal">
START
REPLICA
</code>
</a>
statement.
</p>
<p>
This system variable is read-only and can be set by using
the
<code class="literal">
PERSIST_ONLY
</code>
keyword or the
<code class="literal">
@@persist_only
</code>
qualifier with the
<a class="link" href="set.html" title="13.3.6 The SET Type">
<code class="literal">
SET
</code>
</a>
statement. The
<a class="link" href="replication-options-replica.html#option_mysqld_skip-replica-start">
<code class="option">
--skip-replica-start
</code>
</a>
command
line option also sets this system variable. You can use the
system variable in place of the command line option to allow
access to this feature using MySQL Server’s privilege
structure, so that database administrators do not need any
privileged access to the operating system.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_skip_slave_start">
</a>
<a class="link" href="replication-options-replica.html#sysvar_skip_slave_start">
<code class="literal">
skip_slave_start
</code>
</a>
</p>
<a class="indexterm" name="idm46045141839824">
</a>
<a class="indexterm" name="idm46045141838736">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for skip-slave-start">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--skip-slave-start[={OFF|ON}]
</code>
</td>
</tr>
<tr>
<th>
Deprecated
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_skip_slave_start">
skip_slave_start
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
No
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Boolean
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
OFF
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
Deprecated synonym for
<a class="link" href="replication-options-replica.html#option_mysqld_skip-replica-start">
<code class="option">
--skip-replica-start
</code>
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_slave_checkpoint_group">
</a>
<a class="link" href="replication-options-replica.html#sysvar_slave_checkpoint_group">
<code class="literal">
slave_checkpoint_group
</code>
</a>
</p>
<a class="indexterm" name="idm46045141811232">
</a>
<a class="indexterm" name="idm46045141809744">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for slave_checkpoint_group">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--slave-checkpoint-group=#
</code>
</td>
</tr>
<tr>
<th>
Deprecated
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_slave_checkpoint_group">
slave_checkpoint_group
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Integer
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
512
</code>
</td>
</tr>
<tr>
<th>
Minimum Value
</th>
<td>
<code class="literal">
32
</code>
</td>
</tr>
<tr>
<th>
Maximum Value
</th>
<td>
<code class="literal">
524280
</code>
</td>
</tr>
<tr>
<th>
<a class="link" href="server-system-variables.html#system-variables-block-size" title="Note">
Block Size
</a>
</th>
<td>
<code class="literal">
8
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
Deprecated synonym for
<a class="link" href="replication-options-replica.html#sysvar_replica_checkpoint_group">
<code class="literal">
replica_checkpoint_group
</code>
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_slave_checkpoint_period">
</a>
<a class="link" href="replication-options-replica.html#sysvar_slave_checkpoint_period">
<code class="literal">
slave_checkpoint_period
</code>
</a>
</p>
<a class="indexterm" name="idm46045141774544">
</a>
<a class="indexterm" name="idm46045141773056">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for slave_checkpoint_period">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--slave-checkpoint-period=#
</code>
</td>
</tr>
<tr>
<th>
Deprecated
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_slave_checkpoint_period">
slave_checkpoint_period
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Integer
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
300
</code>
</td>
</tr>
<tr>
<th>
Minimum Value
</th>
<td>
<code class="literal">
1
</code>
</td>
</tr>
<tr>
<th>
Maximum Value
</th>
<td>
<code class="literal">
4294967295
</code>
</td>
</tr>
<tr>
<th>
Unit
</th>
<td>
milliseconds
</td>
</tr>
</tbody>
</table>
</div>
<p>
Deprecated synonym for
<a class="link" href="replication-options-replica.html#sysvar_replica_checkpoint_period">
<code class="literal">
replica_checkpoint_period
</code>
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_slave_compressed_protocol">
</a>
<a class="link" href="replication-options-replica.html#sysvar_slave_compressed_protocol">
<code class="literal">
slave_compressed_protocol
</code>
</a>
</p>
<a class="indexterm" name="idm46045141738736">
</a>
<a class="indexterm" name="idm46045141737632">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for slave_compressed_protocol">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--slave-compressed-protocol[={OFF|ON}]
</code>
</td>
</tr>
<tr>
<th>
Deprecated
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_slave_compressed_protocol">
slave_compressed_protocol
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Boolean
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
OFF
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
Deprecated alias for
<a class="link" href="replication-options-replica.html#sysvar_replica_compressed_protocol">
<code class="literal">
replica_compressed_protocol
</code>
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_slave_exec_mode">
</a>
<a class="link" href="replication-options-replica.html#sysvar_slave_exec_mode">
<code class="literal">
slave_exec_mode
</code>
</a>
</p>
<a class="indexterm" name="idm46045141709872">
</a>
<a class="indexterm" name="idm46045141708784">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for slave_exec_mode">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--slave-exec-mode=mode
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_slave_exec_mode">
slave_exec_mode
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Enumeration
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<p class="valid-value">
<code class="literal">
IDEMPOTENT
</code>
(NDB)
</p>
<p class="valid-value">
<code class="literal">
STRICT
</code>
(Other)
</p>
</td>
</tr>
<tr>
<th>
Valid Values
</th>
<td>
<p class="valid-value">
<code class="literal">
STRICT
</code>
</p>
<p class="valid-value">
<code class="literal">
IDEMPOTENT
</code>
</p>
</td>
</tr>
</tbody>
</table>
</div>
<p>
Deprecated alias for
<a class="link" href="replication-options-replica.html#sysvar_replica_exec_mode">
<code class="literal">
replica_exec_mode
</code>
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_slave_load_tmpdir">
</a>
<a class="link" href="replication-options-replica.html#sysvar_slave_load_tmpdir">
<code class="literal">
slave_load_tmpdir
</code>
</a>
</p>
<a class="indexterm" name="idm46045141677520">
</a>
<a class="indexterm" name="idm46045141676480">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for slave_load_tmpdir">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--slave-load-tmpdir=dir_name
</code>
</td>
</tr>
<tr>
<th>
Deprecated
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_slave_load_tmpdir">
slave_load_tmpdir
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
No
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Directory name
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
Value of --tmpdir
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
Deprecated alias for
<a class="link" href="replication-options-replica.html#sysvar_replica_load_tmpdir">
<code class="literal">
replica_load_tmpdir
</code>
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_slave_max_allowed_packet">
</a>
<a class="link" href="replication-options-replica.html#sysvar_slave_max_allowed_packet">
<code class="literal">
slave_max_allowed_packet
</code>
</a>
</p>
<a class="indexterm" name="idm46045141648672">
</a>
<a class="indexterm" name="idm46045141647568">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for slave_max_allowed_packet">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--slave-max-allowed-packet=#
</code>
</td>
</tr>
<tr>
<th>
Deprecated
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_slave_max_allowed_packet">
slave_max_allowed_packet
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Integer
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
1073741824
</code>
</td>
</tr>
<tr>
<th>
Minimum Value
</th>
<td>
<code class="literal">
1024
</code>
</td>
</tr>
<tr>
<th>
Maximum Value
</th>
<td>
<code class="literal">
1073741824
</code>
</td>
</tr>
<tr>
<th>
Unit
</th>
<td>
bytes
</td>
</tr>
<tr>
<th>
<a class="link" href="server-system-variables.html#system-variables-block-size" title="Note">
Block Size
</a>
</th>
<td>
<code class="literal">
1024
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
Deprecated alias for
<a class="link" href="replication-options-replica.html#sysvar_replica_max_allowed_packet">
<code class="literal">
replica_max_allowed_packet
</code>
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_slave_net_timeout">
</a>
<a class="link" href="replication-options-replica.html#sysvar_slave_net_timeout">
<code class="literal">
slave_net_timeout
</code>
</a>
</p>
<a class="indexterm" name="idm46045141609680">
</a>
<a class="indexterm" name="idm46045141608640">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for slave_net_timeout">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--slave-net-timeout=#
</code>
</td>
</tr>
<tr>
<th>
Deprecated
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_slave_net_timeout">
slave_net_timeout
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Integer
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
60
</code>
</td>
</tr>
<tr>
<th>
Minimum Value
</th>
<td>
<code class="literal">
1
</code>
</td>
</tr>
<tr>
<th>
Maximum Value
</th>
<td>
<code class="literal">
31536000
</code>
</td>
</tr>
<tr>
<th>
Unit
</th>
<td>
seconds
</td>
</tr>
</tbody>
</table>
</div>
<p>
Deprecated alias for
<a class="link" href="replication-options-replica.html#sysvar_replica_net_timeout">
<code class="literal">
replica_net_timeout
</code>
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_slave_parallel_type">
</a>
<a class="link" href="replication-options-replica.html#sysvar_slave_parallel_type">
<code class="literal">
slave_parallel_type
</code>
</a>
</p>
<a class="indexterm" name="idm46045141573872">
</a>
<a class="indexterm" name="idm46045141572832">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for slave_parallel_type">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--slave-parallel-type=value
</code>
</td>
</tr>
<tr>
<th>
Deprecated
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_slave_parallel_type">
slave_parallel_type
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Enumeration
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
LOGICAL_CLOCK
</code>
</td>
</tr>
<tr>
<th>
Valid Values
</th>
<td>
<p class="valid-value">
<code class="literal">
DATABASE
</code>
</p>
<p class="valid-value">
<code class="literal">
LOGICAL_CLOCK
</code>
</p>
</td>
</tr>
</tbody>
</table>
</div>
<p>
Deprecated alias for
<a class="link" href="replication-options-replica.html#sysvar_replica_parallel_type">
<code class="literal">
replica_parallel_type
</code>
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_slave_parallel_workers">
</a>
<a class="link" href="replication-options-replica.html#sysvar_slave_parallel_workers">
<code class="literal">
slave_parallel_workers
</code>
</a>
</p>
<a class="indexterm" name="idm46045141541184">
</a>
<a class="indexterm" name="idm46045141540144">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for slave_parallel_workers">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--slave-parallel-workers=#
</code>
</td>
</tr>
<tr>
<th>
Deprecated
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_slave_parallel_workers">
slave_parallel_workers
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Integer
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
4
</code>
</td>
</tr>
<tr>
<th>
Minimum Value
</th>
<td>
<code class="literal">
0
</code>
</td>
</tr>
<tr>
<th>
Maximum Value
</th>
<td>
<code class="literal">
1024
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
Deprecated alias for
<a class="link" href="replication-options-replica.html#sysvar_replica_parallel_workers">
<code class="literal">
replica_parallel_workers
</code>
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_slave_pending_jobs_size_max">
</a>
<a class="link" href="replication-options-replica.html#sysvar_slave_pending_jobs_size_max">
<code class="literal">
slave_pending_jobs_size_max
</code>
</a>
</p>
<a class="indexterm" name="idm46045141507488">
</a>
<a class="indexterm" name="idm46045141505984">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for slave_pending_jobs_size_max">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--slave-pending-jobs-size-max=#
</code>
</td>
</tr>
<tr>
<th>
Deprecated
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_slave_pending_jobs_size_max">
slave_pending_jobs_size_max
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Integer
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
128M
</code>
</td>
</tr>
<tr>
<th>
Minimum Value
</th>
<td>
<code class="literal">
1024
</code>
</td>
</tr>
<tr>
<th>
Maximum Value
</th>
<td>
<code class="literal">
16EiB
</code>
</td>
</tr>
<tr>
<th>
Unit
</th>
<td>
bytes
</td>
</tr>
<tr>
<th>
<a class="link" href="server-system-variables.html#system-variables-block-size" title="Note">
Block Size
</a>
</th>
<td>
<code class="literal">
1024
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
Deprecated alias for
<a class="link" href="replication-options-replica.html#sysvar_replica_pending_jobs_size_max">
<code class="literal">
replica_pending_jobs_size_max
</code>
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_slave_preserve_commit_order">
</a>
<a class="link" href="replication-options-replica.html#sysvar_slave_preserve_commit_order">
<code class="literal">
slave_preserve_commit_order
</code>
</a>
</p>
<a class="indexterm" name="idm46045141468576">
</a>
<a class="indexterm" name="idm46045141467072">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for slave_preserve_commit_order">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--slave-preserve-commit-order[={OFF|ON}]
</code>
</td>
</tr>
<tr>
<th>
Deprecated
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_slave_preserve_commit_order">
slave_preserve_commit_order
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Boolean
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
ON
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
Deprecated alias for
<a class="link" href="replication-options-replica.html#sysvar_replica_preserve_commit_order">
<code class="literal">
replica_preserve_commit_order
</code>
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_slave_skip_errors">
</a>
<a class="link" href="replication-options-replica.html#sysvar_slave_skip_errors">
<code class="literal">
slave_skip_errors
</code>
</a>
</p>
<a class="indexterm" name="idm46045141439536">
</a>
<a class="indexterm" name="idm46045141438496">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for slave-skip-errors">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--slave-skip-errors=name
</code>
</td>
</tr>
<tr>
<th>
Deprecated
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_slave_skip_errors">
slave_skip_errors
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
No
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
String
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
OFF
</code>
</td>
</tr>
<tr>
<th>
Valid Values
</th>
<td>
<p class="valid-value">
<code class="literal">
OFF
</code>
</p>
<p class="valid-value">
<code class="literal">
[list of error codes]
</code>
</p>
<p class="valid-value">
<code class="literal">
all
</code>
</p>
<p class="valid-value">
<code class="literal">
ddl_exist_errors
</code>
</p>
</td>
</tr>
</tbody>
</table>
</div>
<p>
Deprecated alias for
<a class="link" href="replication-options-replica.html#sysvar_replica_skip_errors">
<code class="literal">
replica_skip_errors
</code>
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_replica_skip_errors">
</a>
<a class="link" href="replication-options-replica.html#sysvar_replica_skip_errors">
<code class="literal">
replica_skip_errors
</code>
</a>
</p>
<a class="indexterm" name="idm46045141405024">
</a>
<a class="indexterm" name="idm46045141403984">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for replica_skip_errors">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--replica-skip-errors=name
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_replica_skip_errors">
replica_skip_errors
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
No
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
String
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
OFF
</code>
</td>
</tr>
<tr>
<th>
Valid Values
</th>
<td>
<p class="valid-value">
<code class="literal">
OFF
</code>
</p>
<p class="valid-value">
<code class="literal">
[list of error codes]
</code>
</p>
<p class="valid-value">
<code class="literal">
all
</code>
</p>
<p class="valid-value">
<code class="literal">
ddl_exist_errors
</code>
</p>
</td>
</tr>
</tbody>
</table>
</div>
<p>
Normally, replication stops when an error occurs on the
replica, which gives you the opportunity to resolve the
inconsistency in the data manually. This variable causes the
replication SQL thread to continue replication when a
statement returns any of the errors listed in the variable
value.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_slave_sql_verify_checksum">
</a>
<a class="link" href="replication-options-replica.html#sysvar_slave_sql_verify_checksum">
<code class="literal">
slave_sql_verify_checksum
</code>
</a>
</p>
<a class="indexterm" name="idm46045141373424">
</a>
<a class="indexterm" name="idm46045141372320">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for slave_sql_verify_checksum">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--slave-sql-verify-checksum[={OFF|ON}]
</code>
</td>
</tr>
<tr>
<th>
Deprecated
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_slave_sql_verify_checksum">
slave_sql_verify_checksum
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Boolean
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
ON
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
Deprecated alias for
<a class="link" href="replication-options-replica.html#sysvar_replica_sql_verify_checksum">
<code class="literal">
replica_sql_verify_checksum
</code>
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_slave_transaction_retries">
</a>
<a class="link" href="replication-options-replica.html#sysvar_slave_transaction_retries">
<code class="literal">
slave_transaction_retries
</code>
</a>
</p>
<a class="indexterm" name="idm46045141344480">
</a>
<a class="indexterm" name="idm46045141343376">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for slave_transaction_retries">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--slave-transaction-retries=#
</code>
</td>
</tr>
<tr>
<th>
Deprecated
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_slave_transaction_retries">
slave_transaction_retries
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Integer
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
10
</code>
</td>
</tr>
<tr>
<th>
Minimum Value
</th>
<td>
<code class="literal">
0
</code>
</td>
</tr>
<tr>
<th>
Maximum Value (64-bit platforms)
</th>
<td>
<code class="literal">
18446744073709551615
</code>
</td>
</tr>
<tr>
<th>
Maximum Value (32-bit platforms)
</th>
<td>
<code class="literal">
4294967295
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
Deprecated alias for
<a class="link" href="replication-options-replica.html#sysvar_replica_transaction_retries">
<code class="literal">
replica_transaction_retries
</code>
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_slave_type_conversions">
</a>
<a class="link" href="replication-options-replica.html#sysvar_slave_type_conversions">
<code class="literal">
slave_type_conversions
</code>
</a>
</p>
<a class="indexterm" name="idm46045141308160">
</a>
<a class="indexterm" name="idm46045141307120">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for slave_type_conversions">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--slave-type-conversions=set
</code>
</td>
</tr>
<tr>
<th>
Deprecated
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_slave_type_conversions">
slave_type_conversions
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Set
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
</code>
</td>
</tr>
<tr>
<th>
Valid Values
</th>
<td>
<p class="valid-value">
<code class="literal">
ALL_LOSSY
</code>
</p>
<p class="valid-value">
<code class="literal">
ALL_NON_LOSSY
</code>
</p>
<p class="valid-value">
<code class="literal">
ALL_SIGNED
</code>
</p>
<p class="valid-value">
<code class="literal">
ALL_UNSIGNED
</code>
</p>
</td>
</tr>
</tbody>
</table>
</div>
<p>
Deprecated alias for
<a class="link" href="replication-options-replica.html#sysvar_replica_type_conversions">
<code class="literal">
replica_type_conversions
</code>
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_sql_replica_skip_counter">
</a>
<a class="link" href="replication-options-replica.html#sysvar_sql_replica_skip_counter">
<code class="literal">
sql_replica_skip_counter
</code>
</a>
</p>
<a class="indexterm" name="idm46045141273760">
</a>
<a class="indexterm" name="idm46045141272656">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for sql_replica_skip_counter">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_sql_replica_skip_counter">
sql_replica_skip_counter
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Integer
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
0
</code>
</td>
</tr>
<tr>
<th>
Minimum Value
</th>
<td>
<code class="literal">
0
</code>
</td>
</tr>
<tr>
<th>
Maximum Value
</th>
<td>
<code class="literal">
4294967295
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
<a class="link" href="replication-options-replica.html#sysvar_sql_replica_skip_counter">
<code class="literal">
sql_replica_skip_counter
</code>
</a>
specifies the number of events from the source that a
replica should skip. Setting the option has no immediate
effect. The variable applies to the next
<a class="link" href="start-replica.html" title="15.4.2.4 START REPLICA Statement">
<code class="literal">
START REPLICA
</code>
</a>
statement; the
next
<a class="link" href="start-replica.html" title="15.4.2.4 START REPLICA Statement">
<code class="literal">
START REPLICA
</code>
</a>
statement
also changes the value back to 0. When this variable is set
to a nonzero value and there are multiple replication
channels configured, the
<a class="link" href="start-replica.html" title="15.4.2.4 START REPLICA Statement">
<code class="literal">
START
REPLICA
</code>
</a>
statement can only be used with the
<code class="literal">
FOR CHANNEL
<em class="replaceable">
<code>
channel
</code>
</em>
</code>
clause.
</p>
<p>
This option is incompatible with GTID-based replication, and
must not be set to a nonzero value when
<a class="link" href="replication-options-gtids.html#sysvar_gtid_mode">
<code class="literal">
gtid_mode=ON
</code>
</a>
is set. If you
need to skip transactions when employing GTIDs, use
<a class="link" href="replication-options-gtids.html#sysvar_gtid_executed">
<code class="literal">
gtid_executed
</code>
</a>
from the
source instead. If you have enabled GTID assignment on a
replication channel using the
<code class="literal">
ASSIGN_GTIDS_TO_ANONYMOUS_TRANSACTIONS
</code>
option of the
<a class="link" href="change-replication-source-to.html" title="15.4.2.2 CHANGE REPLICATION SOURCE TO Statement">
<code class="literal">
CHANGE REPLICATION SOURCE
TO
</code>
</a>
statement,
<a class="link" href="replication-options-replica.html#sysvar_sql_replica_skip_counter">
<code class="literal">
sql_replica_skip_counter
</code>
</a>
is
available. See
<a class="xref" href="replication-administration-skip.html" title="19.1.7.3 Skipping Transactions">
Section 19.1.7.3, “Skipping Transactions”
</a>
.
</p>
<div class="important" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Important
</div>
<p>
If skipping the number of events specified by setting this
variable would cause the replica to begin in the middle of
an event group, the replica continues to skip until it
finds the beginning of the next event group and begins
from that point. For more information, see
<a class="xref" href="replication-administration-skip.html" title="19.1.7.3 Skipping Transactions">
Section 19.1.7.3, “Skipping Transactions”
</a>
.
</p>
</div>
</li>
<li class="listitem">
<p>
<a name="sysvar_sql_slave_skip_counter">
</a>
<a class="link" href="replication-options-replica.html#sysvar_sql_slave_skip_counter">
<code class="literal">
sql_slave_skip_counter
</code>
</a>
</p>
<a class="indexterm" name="idm46045141230144">
</a>
<a class="indexterm" name="idm46045141229104">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for sql_slave_skip_counter">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Deprecated
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_sql_slave_skip_counter">
sql_slave_skip_counter
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Integer
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
0
</code>
</td>
</tr>
<tr>
<th>
Minimum Value
</th>
<td>
<code class="literal">
0
</code>
</td>
</tr>
<tr>
<th>
Maximum Value
</th>
<td>
<code class="literal">
4294967295
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
Deprecated alias for
<a class="link" href="replication-options-replica.html#sysvar_sql_replica_skip_counter">
<code class="literal">
sql_replica_skip_counter
</code>
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_sync_master_info">
</a>
<a class="link" href="replication-options-replica.html#sysvar_sync_master_info">
<code class="literal">
sync_master_info
</code>
</a>
</p>
<a class="indexterm" name="idm46045141198928">
</a>
<a class="indexterm" name="idm46045141197840">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for sync_master_info">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--sync-master-info=#
</code>
</td>
</tr>
<tr>
<th>
Deprecated
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_sync_master_info">
sync_master_info
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Integer
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
10000
</code>
</td>
</tr>
<tr>
<th>
Minimum Value
</th>
<td>
<code class="literal">
0
</code>
</td>
</tr>
<tr>
<th>
Maximum Value
</th>
<td>
<code class="literal">
4294967295
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
Deprecated alias for
<a class="link" href="replication-options-replica.html#sysvar_sync_source_info">
<code class="literal">
sync_source_info
</code>
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_sync_relay_log">
</a>
<a class="link" href="replication-options-replica.html#sysvar_sync_relay_log">
<code class="literal">
sync_relay_log
</code>
</a>
</p>
<a class="indexterm" name="idm46045141165328">
</a>
<a class="indexterm" name="idm46045141164240">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for sync_relay_log">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--sync-relay-log=#
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_sync_relay_log">
sync_relay_log
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Integer
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
10000
</code>
</td>
</tr>
<tr>
<th>
Minimum Value
</th>
<td>
<code class="literal">
0
</code>
</td>
</tr>
<tr>
<th>
Maximum Value
</th>
<td>
<code class="literal">
4294967295
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
If the value of this variable is greater than 0, the MySQL
server synchronizes its relay log to disk (using
<code class="literal">
fdatasync()
</code>
) after every
<code class="literal">
sync_relay_log
</code>
events are written to the
relay log. Setting this variable takes effect for all
replication channels immediately, including running
channels.
</p>
<p>
Setting
<code class="literal">
sync_relay_log
</code>
to 0 causes no
synchronization to be done to disk; in this case, the server
relies on the operating system to flush the relay log's
contents from time to time as for any other file.
</p>
<p>
A value of 1 is the safest choice because in the event of an
unexpected halt you lose at most one event from the relay
log. However, it is also the slowest choice (unless the disk
has a battery-backed cache, which makes synchronization very
fast). For information on the combination of settings on a
replica that is most resilient to unexpected halts, see
<a class="xref" href="replication-solutions-unexpected-replica-halt.html" title="19.4.2 Handling an Unexpected Halt of a Replica">
Section 19.4.2, “Handling an Unexpected Halt of a Replica”
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_sync_relay_log_info">
</a>
<a class="link" href="replication-options-replica.html#sysvar_sync_relay_log_info">
<code class="literal">
sync_relay_log_info
</code>
</a>
</p>
<a class="indexterm" name="idm46045141130144">
</a>
<a class="indexterm" name="idm46045141129104">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for sync_relay_log_info">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--sync-relay-log-info=#
</code>
</td>
</tr>
<tr>
<th>
Deprecated
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_sync_relay_log_info">
sync_relay_log_info
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Integer
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
10000
</code>
</td>
</tr>
<tr>
<th>
Minimum Value
</th>
<td>
<code class="literal">
0
</code>
</td>
</tr>
<tr>
<th>
Maximum Value
</th>
<td>
<code class="literal">
4294967295
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
The number of transactions after which the replica updates
the applier metadata repository. When the applier metadata
repository is stored as an
<a class="link" href="innodb-storage-engine.html" title="Chapter 17 The InnoDB Storage Engine">
<code class="literal">
InnoDB
</code>
</a>
table, which is the
default, it is updated after every transaction and this
system variable is ignored. If the applier metadata
repository is stored as a file (deprecated), the replica
synchronizes its
<code class="literal">
relay-log.info
</code>
file to
disk (using
<code class="literal">
fdatasync()
</code>
) after this many
transactions.
<code class="literal">
0
</code>
(zero) means that the
file contents are flushed by the operating system only.
Setting this variable takes effect for all replication
channels immediately, including running channels.
</p>
<p>
Since storing applier metadata as a file is deprecated, this
variable is also deprecated, and the server raises a warning
whenever you set it or read its value. You should expect
<code class="literal">
sync_relay_log_info
</code>
to be removed in a
future version of MySQL, and migrate applications now that
may depend on it.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_sync_source_info">
</a>
<a class="link" href="replication-options-replica.html#sysvar_sync_source_info">
<code class="literal">
sync_source_info
</code>
</a>
</p>
<a class="indexterm" name="idm46045141092336">
</a>
<a class="indexterm" name="idm46045141091248">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for sync_source_info">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--sync-source-info=#
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_sync_source_info">
sync_source_info
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Integer
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
10000
</code>
</td>
</tr>
<tr>
<th>
Minimum Value
</th>
<td>
<code class="literal">
0
</code>
</td>
</tr>
<tr>
<th>
Maximum Value
</th>
<td>
<code class="literal">
4294967295
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
<a class="link" href="replication-options-replica.html#sysvar_sync_source_info">
<code class="literal">
sync_source_info
</code>
</a>
specifies
the number of events after which the replica updates the
connection metadata repository. When the connection metadata
repository is stored as an
<a class="link" href="innodb-storage-engine.html" title="Chapter 17 The InnoDB Storage Engine">
<code class="literal">
InnoDB
</code>
</a>
table (the default, it
is updated after this number of events. If the connection
metadata repository is stored as a file (deprecated), the
replica synchronizes its
<code class="literal">
master.info
</code>
file
to disk (using
<code class="literal">
fdatasync()
</code>
) after this
number of events. The default value is 10000, and a zero
value means that the repository is never updated. Setting
this variable takes effect for all replication channels
immediately, including running channels.
</p>
</li>
<li class="listitem">
<p>
<a name="sysvar_terminology_use_previous">
</a>
<a class="link" href="replication-options-replica.html#sysvar_terminology_use_previous">
<code class="literal">
terminology_use_previous
</code>
</a>
</p>
<a class="indexterm" name="idm46045141057392">
</a>
<a class="indexterm" name="idm46045141056288">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for terminology_use_previous">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--terminology-use-previous=#
</code>
</td>
</tr>
<tr>
<th>
System Variable
</th>
<td>
<code class="literal">
<a class="link" href="replication-options-replica.html#sysvar_terminology_use_previous">
terminology_use_previous
</a>
</code>
</td>
</tr>
<tr>
<th>
Scope
</th>
<td>
Global, Session
</td>
</tr>
<tr>
<th>
Dynamic
</th>
<td>
Yes
</td>
</tr>
<tr>
<th>
<a class="link" href="optimizer-hints.html#optimizer-hints-set-var" title="Variable-Setting Hint Syntax">
<code class="literal">
SET_VAR
</code>
</a>
Hint Applies
</th>
<td>
No
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Enumeration
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
NONE
</code>
</td>
</tr>
<tr>
<th>
Valid Values
</th>
<td>
<p class="valid-value">
<code class="literal">
NONE
</code>
</p>
<p class="valid-value">
<code class="literal">
BEFORE_8_0_26
</code>
</p>
<p class="valid-value">
<code class="literal">
BEFORE_8_2_0
</code>
</p>
</td>
</tr>
</tbody>
</table>
</div>
<p>
Incompatible changes were made in MySQL 8.0 to
instrumentation names containing the terms
<code class="literal">
master
</code>
,
<code class="literal">
slave
</code>
, and
<code class="literal">
mts
</code>
(for
<span class="quote">
“
<span class="quote">
Multi-Threaded
Slave
</span>
”
</span>
), which were changed respectively to
<code class="literal">
source
</code>
,
<code class="literal">
replica
</code>
, and
<code class="literal">
mta
</code>
(for
<span class="quote">
“
<span class="quote">
Multi-Threaded
Applier
</span>
”
</span>
). If these incompatible changes impact your
applications, set
<code class="literal">
terminology_use_previous
</code>
to
<code class="literal">
BEFORE_8_0_26
</code>
to make the MySQL server
use the old versions of the names for the objects specified
in the previous list. This enables monitoring tools that
rely on the old names to continue working until they can be
updated to use the new names.
</p>
<p>
MySQL 8.4 normally displays
<code class="literal">
REPLICA_SIDE_DISABLED
</code>
rather than
<code class="literal">
SLAVESIDE_DISABLED
</code>
in the output of
<code class="literal">
SHOW CREATE EVENT
</code>
,
<code class="literal">
SHOW
EVENTS
</code>
, and queries against the Information Schema
<code class="literal">
EVENTS
</code>
table. You can cause
<code class="literal">
SLAVESIDE_DISABLED
</code>
to be shown instead by
setting
<code class="literal">
terminology_use_previous
</code>
to
<code class="literal">
BEFORE_8_0_26
</code>
or
<code class="literal">
BEFORE_8_2_0
</code>
.
</p>
<p>
Set the
<a class="link" href="replication-options-replica.html#sysvar_terminology_use_previous">
<code class="literal">
terminology_use_previous
</code>
</a>
system variable with session scope to support individual
users, or with global scope to be the default for all new
sessions. When global scope is used, the slow query log
contains the old versions of the names.
</p>
<p>
The affected instrumentation names are given in the
following list. The
<a class="link" href="replication-options-replica.html#sysvar_terminology_use_previous">
<code class="literal">
terminology_use_previous
</code>
</a>
system variable only affects these items. It does not affect
the new aliases for system variables, status variables, and
command-line options that were also introduced in MySQL 8.0,
and these can still be used when it is enabled.
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<p>
Instrumented locks (mutexes), visible in the
<code class="literal">
mutex_instances
</code>
and
<code class="literal">
events_waits_*
</code>
Performance Schema
tables with the prefix
<code class="literal">
wait/synch/mutex/
</code>
</p>
</li>
<li class="listitem">
<p>
Read/write locks, visible in the
<code class="literal">
rwlock_instances
</code>
and
<code class="literal">
events_waits_*
</code>
Performance Schema
tables with the prefix
<code class="literal">
wait/synch/rwlock/
</code>
</p>
</li>
<li class="listitem">
<p>
Instrumented condition variables, visible in the
<code class="literal">
cond_instances
</code>
and
<code class="literal">
events_waits_*
</code>
Performance Schema
tables with the prefix
<code class="literal">
wait/synch/cond/
</code>
</p>
</li>
<li class="listitem">
<p>
Instrumented memory allocations, visible in the
<code class="literal">
memory_summary_*
</code>
Performance Schema
tables with the prefix
<code class="literal">
memory/sql/
</code>
</p>
</li>
<li class="listitem">
<p>
Thread names, visible in the
<code class="literal">
threads
</code>
Performance Schema table with the prefix
<code class="literal">
thread/sql/
</code>
</p>
</li>
<li class="listitem">
<p>
Thread stages, visible in the
<code class="literal">
events_stages_*
</code>
Performance Schema
tables with the prefix
<code class="literal">
stage/sql/
</code>
,
and without the prefix in the
<code class="literal">
threads
</code>
and
<code class="literal">
processlist
</code>
Performance Schema
tables, the output from the
<code class="literal">
SHOW
PROCESSLIST
</code>
statement, the Information Schema
<code class="literal">
processlist
</code>
table, and the slow query
log
</p>
</li>
<li class="listitem">
<p>
Thread commands, visible in the
<code class="literal">
events_statements_history*
</code>
and
<code class="literal">
events_statements_summary_*_by_event_name
</code>
Performance Schema tables with the prefix
<code class="literal">
statement/com/
</code>
, and without the
prefix in the
<code class="literal">
threads
</code>
and
<code class="literal">
processlist
</code>
Performance Schema
tables, the output from the
<code class="literal">
SHOW
PROCESSLIST
</code>
statement, the Information Schema
<code class="literal">
processlist
</code>
table, and the output
from the
<code class="literal">
SHOW REPLICA STATUS
</code>
statement
</p>
</li>
</ul>
</div>
</li>
</ul>
</div>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/identifier-length.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="identifier-length">
</a>
11.2.1 Identifier Length Limits
</h3>
</div>
</div>
</div>
<p>
The following table describes the maximum length for each type
of identifier.
</p>
<div class="informaltable">
<table summary="The maximum length for each type of MySQL object identifier.">
<colgroup>
<col style="width: 15%"/>
<col style="width: 15%"/>
</colgroup>
<thead>
<tr>
<th>
Identifier Type
</th>
<th>
Maximum Length (characters)
</th>
</tr>
</thead>
<tbody>
<tr>
<td>
Database
</td>
<td>
64
</td>
</tr>
<tr>
<td>
Table
</td>
<td>
64
</td>
</tr>
<tr>
<td>
Column
</td>
<td>
64
</td>
</tr>
<tr>
<td>
Index
</td>
<td>
64
</td>
</tr>
<tr>
<td>
Constraint
</td>
<td>
64
</td>
</tr>
<tr>
<td>
Stored Program
</td>
<td>
64
</td>
</tr>
<tr>
<td>
View
</td>
<td>
64
</td>
</tr>
<tr>
<td>
Tablespace
</td>
<td>
64
</td>
</tr>
<tr>
<td>
Server
</td>
<td>
64
</td>
</tr>
<tr>
<td>
Log File Group
</td>
<td>
64
</td>
</tr>
<tr>
<td>
Alias
</td>
<td>
256 (see exception following table)
</td>
</tr>
<tr>
<td>
Compound Statement Label
</td>
<td>
16
</td>
</tr>
<tr>
<td>
User-Defined Variable
</td>
<td>
64
</td>
</tr>
<tr>
<td>
Resource Group
</td>
<td>
64
</td>
</tr>
</tbody>
</table>
</div>
<div class="informaltable">
<table cellpadding="0" cellspacing="0" style="position: fixed; top: 0px; display: none; left: 401px; width: 739px;">
<thead>
<tr>
<th style="width: 369px;">
Identifier Type
</th>
<th style="width: 369px;">
Maximum Length (characters)
</th>
</tr>
</thead>
</table>
</div>
<p>
Aliases for column names in
<a class="link" href="create-view.html" title="15.1.23 CREATE VIEW Statement">
<code class="literal">
CREATE
VIEW
</code>
</a>
statements are checked against the maximum column
length of 64 characters (not the maximum alias length of 256
characters).
</p>
<p>
For constraint definitions that include no constraint name, the
server internally generates a name derived from the associated
table name. For example, internally generated foreign key and
<code class="literal">
CHECK
</code>
constraint names consist of the table
name plus
<code class="literal">
_ibfk_
</code>
or
<code class="literal">
_chk_
</code>
and a number. If the table name is close to the length limit for
constraint names, the additional characters required for the
constraint name may cause that name to exceed the limit,
resulting in an error.
</p>
<p>
Identifiers are stored using Unicode (UTF-8). This applies to
identifiers in table definitions and to identifiers stored in
the grant tables in the
<code class="literal">
mysql
</code>
database. The
sizes of the identifier string columns in the grant tables are
measured in characters. You can use multibyte characters without
reducing the number of characters permitted for values stored in
these columns.
</p>
<p>
Values such as user name and host names in MySQL account names
are strings rather than identifiers. For information about the
maximum length of such values as stored in grant tables, see
<a class="xref" href="grant-tables.html#grant-tables-scope-column-properties" title="Grant Table Scope Column Properties">
Grant Table Scope Column Properties
</a>
.
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/mysql-innodb-cluster-introduction.html | <div id="docs-body">
<div class="chapter">
<div class="titlepage">
<div>
<div>
<h1 class="title">
<a name="mysql-innodb-cluster-introduction">
</a>
Chapter 23 InnoDB Cluster
</h1>
</div>
</div>
</div>
<a class="indexterm" name="idm46045124525200">
</a>
<p>
This chapter introduces MySQL InnoDB Cluster, which combines MySQL
technologies to enable you to deploy and administer a complete
integrated high availability solution for MySQL. This content is a
high-level overview of InnoDB Cluster, for full documentation, see
<a class="ulink" href="/doc/mysql-shell/8.4/en/mysql-innodb-cluster.html" target="_top">
MySQL InnoDB Cluster
</a>
.
</p>
<div class="important" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Important
</div>
<p>
InnoDB Cluster does not provide support for MySQL NDB Cluster. For
more information about MySQL NDB Cluster, see
<a class="xref" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
Chapter 25,
<i>
MySQL NDB Cluster 8.4
</i>
</a>
and
<a class="xref" href="mysql-cluster-compared.html" title="25.2.6 MySQL Server Using InnoDB Compared with NDB Cluster">
Section 25.2.6, “MySQL Server Using InnoDB Compared with NDB Cluster”
</a>
.
</p>
</div>
<p>
An InnoDB Cluster consists of at least three MySQL Server
instances, and it provides high-availability and scaling features.
InnoDB Cluster uses the following MySQL technologies:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<a class="ulink" href="/doc/mysql-shell/8.4/en/" target="_top">
MySQL Shell
</a>
, which is an
advanced client and code editor for MySQL.
</p>
</li>
<li class="listitem">
<p>
MySQL Server, and
<a class="link" href="group-replication.html" title="Chapter 20 Group Replication">
Group
Replication
</a>
, which enables a set of MySQL instances to
provide high-availability. InnoDB Cluster provides an
alternative, easy to use programmatic way to work with Group
Replication.
</p>
</li>
<li class="listitem">
<p>
<a class="ulink" href="/doc/mysql-router/8.4/en/" target="_top">
MySQL Router
</a>
, a lightweight
middleware that provides transparent routing between your
application and InnoDB Cluster.
</p>
</li>
</ul>
</div>
<p>
The following diagram shows an overview of how these technologies
work together:
</p>
<div class="figure">
<a name="innodb-cluster-overview-image">
</a>
<p class="title">
<b>
Figure 23.1 InnoDB Cluster overview
</b>
</p>
<div class="figure-contents">
<div class="mediaobject">
<img alt="Three MySQL servers are grouped together as a high availability cluster. One of the servers is the read/write primary instance, and the other two are read-only secondary instances. Group Replication is used to replicate data from the primary instance to the secondary instances. MySQL Router connects client applications (in this example, a MySQL Connector) to the primary instance." src="images/innodb_cluster_overview.png" style="width: 100%; max-width: 394px;"/>
</div>
</div>
</div>
<br class="figure-break"/>
<p>
Being built on MySQL
<a class="link" href="group-replication.html" title="Chapter 20 Group Replication">
Group
Replication
</a>
, provides features such as automatic membership
management, fault tolerance, automatic failover, and so on. An
InnoDB Cluster usually runs in a single-primary mode, with one
primary instance (read-write) and multiple secondary instances
(read-only). Advanced users can also take advantage of a
<a class="link" href="group-replication-multi-primary-mode.html" title="20.1.3.2 Multi-Primary Mode">
multi-primary
</a>
mode, where all instances are primaries. You can even change the
topology of the cluster while InnoDB Cluster is online, to ensure
the highest possible availability.
</p>
<p>
You work with InnoDB Cluster using the
<a class="ulink" href="/doc/mysql-shell/8.4/en/admin-api-overview.html" target="_top">
AdminAPI
</a>
, provided as
part of MySQL Shell. AdminAPI is available in JavaScript and
Python, and is well suited to scripting and automation of
deployments of MySQL to achieve high-availability and scalability.
By using MySQL Shell's AdminAPI, you can avoid the need to
configure many instances manually. Instead, AdminAPI provides an
effective modern interface to sets of MySQL instances and enables
you to provision, administer, and monitor your deployment from one
central tool.
</p>
<p>
To get started with InnoDB Cluster you need to
<a class="ulink" href="https://dev.mysql.com/downloads/shell/" target="_top">
download
</a>
and
<a class="ulink" href="/doc/mysql-shell/8.4/en/mysql-shell-install.html" target="_top">
install
</a>
MySQL Shell.
You need some hosts with MySQL Server instances
<a class="link" href="installing.html" title="Chapter 2 Installing MySQL">
installed
</a>
, and you can also
<a class="ulink" href="/doc/mysql-router/8.4/en/mysql-router-installation.html" target="_top">
install
</a>
MySQL Router.
</p>
<p>
InnoDB Cluster supports
<a class="link" href="clone-plugin.html" title="7.6.7 The Clone Plugin">
MySQL
Clone
</a>
, which enables you to provision instances simply. In
the past, to provision a new instance before it joins a set of MySQL
instances you would need to somehow manually transfer the
transactions to the joining instance. This could involve making file
copies, manually copying them, and so on. Using InnoDB Cluster,
you can simply
<a class="ulink" href="/doc/mysql-shell/8.4/en/add-instances-cluster.html" target="_top">
add an
instance
</a>
to the cluster and it is automatically provisioned.
</p>
<p>
Similarly, InnoDB Cluster is tightly integrated with
<a class="ulink" href="/doc/mysql-router/8.4/en/" target="_top">
MySQL Router
</a>
, and you can use
AdminAPI to
<a class="ulink" href="/doc/mysql-shell/8.4/en/registered-routers.html" target="_top">
work with
</a>
them together. MySQL Router can automatically configure itself based on
an InnoDB Cluster, in a process called
<a class="ulink" href="/doc/mysql-shell/8.4/en/admin-api-bootstrapping-router.html" target="_top">
bootstrapping
</a>
,
which removes the need for you to configure routing manually.
MySQL Router then transparently connects client applications to the
InnoDB Cluster, providing routing and load-balancing for client
connections. This integration also enables you to administer some
aspects of a MySQL Router bootstrapped against an InnoDB Cluster using
AdminAPI. InnoDB Cluster status information includes details
about MySQL Routers bootstrapped against the cluster. Operations enable
you to
<a class="ulink" href="/doc/mysql-shell/8.4/en/configuring-router-user.html" target="_top">
create MySQL Router
users
</a>
at the cluster level, to work with the MySQL Routers
bootstrapped against the cluster, and so on.
</p>
<p>
For more information on these technologies, see the user
documentation linked in the descriptions. In addition to this user
documentation, there is developer documentation for all AdminAPI
methods in the MySQL Shell JavaScript API Reference or MySQL Shell
Python API Reference, available from
<a class="ulink" href="/doc/index-connectors.html" target="_top">
Connectors and APIs
</a>
.
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/backup-policy.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="backup-policy">
</a>
9.3.1 Establishing a Backup Policy
</h3>
</div>
</div>
</div>
<p>
To be useful, backups must be scheduled regularly. A full backup
(a snapshot of the data at a point in time) can be done in MySQL
with several tools. For example,
<a class="link" href="mysql-enterprise-backup.html" title="32.1 MySQL Enterprise Backup Overview">
MySQL Enterprise Backup
</a>
can perform
a
<a class="link" href="glossary.html#glos_physical_backup" title="physical backup">
physical backup
</a>
of
an entire instance, with optimizations to minimize overhead and
avoid disruption when backing up
<code class="literal">
InnoDB
</code>
data
files;
<a class="link" href="mysqldump.html" title="6.5.4 mysqldump — A Database Backup Program">
<span class="command">
<strong>
mysqldump
</strong>
</span>
</a>
provides online
<a class="link" href="glossary.html#glos_logical_backup" title="logical backup">
logical backup
</a>
. This
discussion uses
<a class="link" href="mysqldump.html" title="6.5.4 mysqldump — A Database Backup Program">
<span class="command">
<strong>
mysqldump
</strong>
</span>
</a>
.
</p>
<p>
Assume that we make a full backup of all our
<code class="literal">
InnoDB
</code>
tables in all databases using the
following command on Sunday at 1 p.m., when load is low:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-terminal"><div class="docs-select-all right" id="sa77511381"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-terminal"><span class="token prompt">$> </span><span class="token command">mysqldump</span> <span class="token property">--all-databases</span> <span class="token property">--source-data</span> <span class="token property">--single-transaction</span> > backup_sunday_1_PM<span class="token punctuation">.</span>sql</code></pre>
</div>
<p>
The resulting
<code class="filename">
.sql
</code>
file produced by
<a class="link" href="mysqldump.html" title="6.5.4 mysqldump — A Database Backup Program">
<span class="command">
<strong>
mysqldump
</strong>
</span>
</a>
contains a set of SQL
<a class="link" href="insert.html" title="15.2.7 INSERT Statement">
<code class="literal">
INSERT
</code>
</a>
statements that can be
used to reload the dumped tables at a later time.
</p>
<p>
This backup operation acquires a global read lock on all tables
at the beginning of the dump (using
<a class="link" href="flush.html#flush-tables-with-read-lock">
<code class="literal">
FLUSH
TABLES WITH READ LOCK
</code>
</a>
). As soon as this lock has been
acquired, the binary log coordinates are read and the lock is
released. If long updating statements are running when the
<a class="link" href="flush.html" title="15.7.8.3 FLUSH Statement">
<code class="literal">
FLUSH
</code>
</a>
statement is issued, the
backup operation may stall until those statements finish. After
that, the dump becomes lock-free and does not disturb reads and
writes on the tables.
</p>
<p>
It was assumed earlier that the tables to back up are
<code class="literal">
InnoDB
</code>
tables, so
<a class="link" href="mysqldump.html#option_mysqldump_single-transaction">
<code class="option">
--single-transaction
</code>
</a>
uses a
consistent read and guarantees that data seen by
<a class="link" href="mysqldump.html" title="6.5.4 mysqldump — A Database Backup Program">
<span class="command">
<strong>
mysqldump
</strong>
</span>
</a>
does not change. (Changes made by
other clients to
<code class="literal">
InnoDB
</code>
tables are not seen
by the
<a class="link" href="mysqldump.html" title="6.5.4 mysqldump — A Database Backup Program">
<span class="command">
<strong>
mysqldump
</strong>
</span>
</a>
process.) If the backup
operation includes nontransactional tables, consistency requires
that they do not change during the backup. For example, for the
<code class="literal">
MyISAM
</code>
tables in the
<code class="literal">
mysql
</code>
database, there must be no administrative changes to MySQL
accounts during the backup.
</p>
<p>
Full backups are necessary, but it is not always convenient to
create them. They produce large backup files and take time to
generate. They are not optimal in the sense that each successive
full backup includes all data, even that part that has not
changed since the previous full backup. It is more efficient to
make an initial full backup, and then to make incremental
backups. The incremental backups are smaller and take less time
to produce. The tradeoff is that, at recovery time, you cannot
restore your data just by reloading the full backup. You must
also process the incremental backups to recover the incremental
changes.
</p>
<p>
To make incremental backups, we need to save the incremental
changes. In MySQL, these changes are represented in the binary
log, so the MySQL server should always be started with the
<a class="link" href="replication-options-binary-log.html#option_mysqld_log-bin">
<code class="option">
--log-bin
</code>
</a>
option to enable that
log. With binary logging enabled, the server writes each data
change into a file while it updates data. Looking at the data
directory of a MySQL server that has been running for some days,
we find these MySQL binary log files:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-simple"><div class="docs-select-all right" id="sa81602084"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-simple"><span class="token operator">-</span>rw<span class="token operator">-</span>rw<span class="token operator">--</span><span class="token operator">--</span> 1 guilhem guilhem 1277324 Nov 10 23<span class="token operator">:</span>59 gbichot2<span class="token operator">-</span>bin<span class="token punctuation">.</span>000001
<span class="token operator">-</span>rw<span class="token operator">-</span>rw<span class="token operator">--</span><span class="token operator">--</span> 1 guilhem guilhem 4 Nov 10 23<span class="token operator">:</span>59 gbichot2<span class="token operator">-</span>bin<span class="token punctuation">.</span>000002
<span class="token operator">-</span>rw<span class="token operator">-</span>rw<span class="token operator">--</span><span class="token operator">--</span> 1 guilhem guilhem 79 Nov 11 11<span class="token operator">:</span>06 gbichot2<span class="token operator">-</span>bin<span class="token punctuation">.</span>000003
<span class="token operator">-</span>rw<span class="token operator">-</span>rw<span class="token operator">--</span><span class="token operator">--</span> 1 guilhem guilhem 508 Nov 11 11<span class="token operator">:</span>08 gbichot2<span class="token operator">-</span>bin<span class="token punctuation">.</span>000004
<span class="token operator">-</span>rw<span class="token operator">-</span>rw<span class="token operator">--</span><span class="token operator">--</span> 1 guilhem guilhem 220047446 Nov 12 16<span class="token operator">:</span>47 gbichot2<span class="token operator">-</span>bin<span class="token punctuation">.</span>000005
<span class="token operator">-</span>rw<span class="token operator">-</span>rw<span class="token operator">--</span><span class="token operator">--</span> 1 guilhem guilhem 998412 Nov 14 10<span class="token operator">:</span>08 gbichot2<span class="token operator">-</span>bin<span class="token punctuation">.</span>000006
<span class="token operator">-</span>rw<span class="token operator">-</span>rw<span class="token operator">--</span><span class="token operator">--</span> 1 guilhem guilhem 361 Nov 14 10<span class="token operator">:</span>07 gbichot2<span class="token operator">-</span>bin<span class="token punctuation">.</span>index</code></pre>
</div>
<p>
Each time it restarts, the MySQL server creates a new binary log
file using the next number in the sequence. While the server is
running, you can also tell it to close the current binary log
file and begin a new one manually by issuing a
<a class="link" href="flush.html#flush-logs">
<code class="literal">
FLUSH LOGS
</code>
</a>
SQL statement or with
a
<a class="link" href="mysqladmin.html" title="6.5.2 mysqladmin — A MySQL Server Administration Program">
<span class="command">
<strong>
mysqladmin flush-logs
</strong>
</span>
</a>
command.
<a class="link" href="mysqldump.html" title="6.5.4 mysqldump — A Database Backup Program">
<span class="command">
<strong>
mysqldump
</strong>
</span>
</a>
also has an option to flush the
logs. The
<code class="literal">
.index
</code>
file in the data directory
contains the list of all MySQL binary logs in the directory.
</p>
<p>
The MySQL binary logs are important for recovery because they
form the set of incremental backups. If you make sure to flush
the logs when you make your full backup, the binary log files
created afterward contain all the data changes made since the
backup. Let's modify the previous
<a class="link" href="mysqldump.html" title="6.5.4 mysqldump — A Database Backup Program">
<span class="command">
<strong>
mysqldump
</strong>
</span>
</a>
command a bit so that it flushes the MySQL binary logs at the
moment of the full backup, and so that the dump file contains
the name of the new current binary log:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-terminal"><div class="docs-select-all right" id="sa89859330"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-terminal"><span class="token prompt">$> </span><span class="token command">mysqldump</span> <span class="token property">--single-transaction</span> <span class="token property">--flush-logs</span> <span class="token constant">--source-data</span><span class="token attr-value"><span class="token punctuation">=</span>2</span> \
<span class="token property">--all-databases</span> > backup_sunday_1_PM<span class="token punctuation">.</span>sql</code></pre>
</div>
<p>
After executing this command, the data directory contains a new
binary log file,
<code class="filename">
gbichot2-bin.000007
</code>
,
because the
<a class="link" href="mysqldump.html#option_mysqldump_flush-logs">
<code class="option">
--flush-logs
</code>
</a>
option causes the server to flush its logs. The
<a class="link" href="mysqldump.html#option_mysqldump_source-data">
<code class="option">
--source-data
</code>
</a>
option causes
<a class="link" href="mysqldump.html" title="6.5.4 mysqldump — A Database Backup Program">
<span class="command">
<strong>
mysqldump
</strong>
</span>
</a>
to write binary log information to
its output, so the resulting
<code class="filename">
.sql
</code>
dump file
includes these lines:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-simple"><div class="docs-select-all right" id="sa31677991"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-simple"><span class="token operator">--</span> Position to start replication or point<span class="token operator">-</span>in<span class="token operator">-</span>time recovery from
<span class="token operator">--</span> CHANGE REPLICATION SOURCE TO SOURCE_LOG_FILE<span class="token operator">=</span>'gbichot2<span class="token operator">-</span>bin<span class="token punctuation">.</span>000007'<span class="token punctuation">,</span>SOURCE_LOG_POS<span class="token operator">=</span>4<span class="token punctuation">;</span></code></pre>
</div>
<p>
Because the
<a class="link" href="mysqldump.html" title="6.5.4 mysqldump — A Database Backup Program">
<span class="command">
<strong>
mysqldump
</strong>
</span>
</a>
command made a full
backup, those lines mean two things:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
The dump file contains all changes made before any changes
written to the
<code class="filename">
gbichot2-bin.000007
</code>
binary log file or higher.
</p>
</li>
<li class="listitem">
<p>
All data changes logged after the backup are not present in
the dump file, but are present in the
<code class="filename">
gbichot2-bin.000007
</code>
binary log file or
higher.
</p>
</li>
</ul>
</div>
<p>
On Monday at 1 p.m., we can create an incremental backup by
flushing the logs to begin a new binary log file. For example,
executing a
<a class="link" href="mysqladmin.html" title="6.5.2 mysqladmin — A MySQL Server Administration Program">
<span class="command">
<strong>
mysqladmin flush-logs
</strong>
</span>
</a>
command
creates
<code class="filename">
gbichot2-bin.000008
</code>
. All changes
between the Sunday 1 p.m. full backup and Monday 1 p.m. are
written in
<code class="filename">
gbichot2-bin.000007
</code>
. This
incremental backup is important, so it is a good idea to copy it
to a safe place. (For example, back it up on tape or DVD, or
copy it to another machine.) On Tuesday at 1 p.m., execute
another
<a class="link" href="mysqladmin.html" title="6.5.2 mysqladmin — A MySQL Server Administration Program">
<span class="command">
<strong>
mysqladmin flush-logs
</strong>
</span>
</a>
command. All
changes between Monday 1 p.m. and Tuesday 1 p.m. are written in
<code class="filename">
gbichot2-bin.000008
</code>
(which also should be
copied somewhere safe).
</p>
<p>
The MySQL binary logs take up disk space. To free up space,
purge them from time to time. One way to do this is by deleting
the binary logs that are no longer needed, such as when we make
a full backup:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-terminal"><div class="docs-select-all right" id="sa78319973"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-terminal"><span class="token prompt">$> </span><span class="token command">mysqldump</span> <span class="token property">--single-transaction</span> <span class="token property">--flush-logs</span> <span class="token constant">--source-data</span><span class="token attr-value"><span class="token punctuation">=</span>2</span> \
<span class="token property">--all-databases</span> <span class="token property">--delete-source-logs</span> > backup_sunday_1_PM<span class="token punctuation">.</span>sql</code></pre>
</div>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
Deleting the MySQL binary logs with
<a class="link" href="mysqldump.html" title="6.5.4 mysqldump — A Database Backup Program">
<span class="command">
<strong>
mysqldump
</strong>
</span>
</a>
<a class="link" href="mysqldump.html#option_mysqldump_delete-source-logs">
<code class="option">
--delete-source-logs
</code>
</a>
can be
dangerous if your server is a replication source server,
because replicas might not yet fully have processed the
contents of the binary log. The description for the
<a class="link" href="purge-binary-logs.html" title="15.4.1.1 PURGE BINARY LOGS Statement">
<code class="literal">
PURGE BINARY LOGS
</code>
</a>
statement
explains what should be verified before deleting the MySQL
binary logs. See
<a class="xref" href="purge-binary-logs.html" title="15.4.1.1 PURGE BINARY LOGS Statement">
Section 15.4.1.1, “PURGE BINARY LOGS Statement”
</a>
.
</p>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/create-table.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="create-table">
</a>
15.1.20 CREATE TABLE Statement
</h3>
</div>
</div>
</div>
<div class="toc">
<dl class="toc">
<dt>
<span class="section">
<a href="create-table-files.html">
15.1.20.1 Files Created by CREATE TABLE
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="create-temporary-table.html">
15.1.20.2 CREATE TEMPORARY TABLE Statement
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="create-table-like.html">
15.1.20.3 CREATE TABLE ... LIKE Statement
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="create-table-select.html">
15.1.20.4 CREATE TABLE ... SELECT Statement
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="create-table-foreign-keys.html">
15.1.20.5 FOREIGN KEY Constraints
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="create-table-check-constraints.html">
15.1.20.6 CHECK Constraints
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="silent-column-changes.html">
15.1.20.7 Silent Column Specification Changes
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="create-table-generated-columns.html">
15.1.20.8 CREATE TABLE and Generated Columns
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="create-table-secondary-indexes.html">
15.1.20.9 Secondary Indexes and Generated Columns
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="invisible-columns.html">
15.1.20.10 Invisible Columns
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="create-table-gipks.html">
15.1.20.11 Generated Invisible Primary Keys
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="create-table-ndb-comment-options.html">
15.1.20.12 Setting NDB Comment Options
</a>
</span>
</dt>
</dl>
</div>
<a class="indexterm" name="idm46045186637392">
</a>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa92168710"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token punctuation">[</span><span class="token keyword">TEMPORARY</span><span class="token punctuation">]</span> <span class="token keyword">TABLE</span> <span class="token punctuation">[</span><span class="token keyword">IF</span> <span class="token operator">NOT</span> <span class="token keyword">EXISTS</span><span class="token punctuation">]</span> <em class="replaceable">tbl_name</em>
<span class="token punctuation">(</span><em class="replaceable">create_definition</em><span class="token punctuation">,</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">)</span>
<span class="token punctuation">[</span><em class="replaceable">table_options</em><span class="token punctuation">]</span>
<span class="token punctuation">[</span><em class="replaceable">partition_options</em><span class="token punctuation">]</span>
<span class="token keyword">CREATE</span> <span class="token punctuation">[</span><span class="token keyword">TEMPORARY</span><span class="token punctuation">]</span> <span class="token keyword">TABLE</span> <span class="token punctuation">[</span><span class="token keyword">IF</span> <span class="token operator">NOT</span> <span class="token keyword">EXISTS</span><span class="token punctuation">]</span> <em class="replaceable">tbl_name</em>
<span class="token punctuation">[</span><span class="token punctuation">(</span><em class="replaceable">create_definition</em><span class="token punctuation">,</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">)</span><span class="token punctuation">]</span>
<span class="token punctuation">[</span><em class="replaceable">table_options</em><span class="token punctuation">]</span>
<span class="token punctuation">[</span><em class="replaceable">partition_options</em><span class="token punctuation">]</span>
<span class="token punctuation">[</span><span class="token keyword">IGNORE</span> <span class="token operator">|</span> <span class="token keyword">REPLACE</span><span class="token punctuation">]</span>
<span class="token punctuation">[</span><span class="token keyword">AS</span><span class="token punctuation">]</span> <em class="replaceable">query_expression</em>
<span class="token keyword">CREATE</span> <span class="token punctuation">[</span><span class="token keyword">TEMPORARY</span><span class="token punctuation">]</span> <span class="token keyword">TABLE</span> <span class="token punctuation">[</span><span class="token keyword">IF</span> <span class="token operator">NOT</span> <span class="token keyword">EXISTS</span><span class="token punctuation">]</span> <em class="replaceable">tbl_name</em>
{ <span class="token operator">LIKE</span> <em class="replaceable">old_tbl_name</em> <span class="token operator">|</span> <span class="token punctuation">(</span><span class="token operator">LIKE</span> <em class="replaceable">old_tbl_name</em><span class="token punctuation">)</span> }
<em class="replaceable">create_definition</em>: {
<em class="replaceable">col_name</em> <em class="replaceable">column_definition</em>
<span class="token operator">|</span> {<span class="token keyword">INDEX</span> <span class="token operator">|</span> <span class="token keyword">KEY</span>} <span class="token punctuation">[</span><em class="replaceable">index_name</em><span class="token punctuation">]</span> <span class="token punctuation">[</span><em class="replaceable">index_type</em><span class="token punctuation">]</span> <span class="token punctuation">(</span><em class="replaceable">key_part</em><span class="token punctuation">,</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">)</span>
<span class="token punctuation">[</span><em class="replaceable">index_option</em><span class="token punctuation">]</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token operator">|</span> {<span class="token keyword">FULLTEXT</span> <span class="token operator">|</span> <span class="token keyword">SPATIAL</span>} <span class="token punctuation">[</span><span class="token keyword">INDEX</span> <span class="token operator">|</span> <span class="token keyword">KEY</span><span class="token punctuation">]</span> <span class="token punctuation">[</span><em class="replaceable">index_name</em><span class="token punctuation">]</span> <span class="token punctuation">(</span><em class="replaceable">key_part</em><span class="token punctuation">,</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">)</span>
<span class="token punctuation">[</span><em class="replaceable">index_option</em><span class="token punctuation">]</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token operator">|</span> <span class="token punctuation">[</span><span class="token keyword">CONSTRAINT</span> <span class="token punctuation">[</span><em class="replaceable">symbol</em><span class="token punctuation">]</span><span class="token punctuation">]</span> <span class="token keyword">PRIMARY</span> <span class="token keyword">KEY</span>
<span class="token punctuation">[</span><em class="replaceable">index_type</em><span class="token punctuation">]</span> <span class="token punctuation">(</span><em class="replaceable">key_part</em><span class="token punctuation">,</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">)</span>
<span class="token punctuation">[</span><em class="replaceable">index_option</em><span class="token punctuation">]</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token operator">|</span> <span class="token punctuation">[</span><span class="token keyword">CONSTRAINT</span> <span class="token punctuation">[</span><em class="replaceable">symbol</em><span class="token punctuation">]</span><span class="token punctuation">]</span> <span class="token keyword">UNIQUE</span> <span class="token punctuation">[</span><span class="token keyword">INDEX</span> <span class="token operator">|</span> <span class="token keyword">KEY</span><span class="token punctuation">]</span>
<span class="token punctuation">[</span><em class="replaceable">index_name</em><span class="token punctuation">]</span> <span class="token punctuation">[</span><em class="replaceable">index_type</em><span class="token punctuation">]</span> <span class="token punctuation">(</span><em class="replaceable">key_part</em><span class="token punctuation">,</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">)</span>
<span class="token punctuation">[</span><em class="replaceable">index_option</em><span class="token punctuation">]</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token operator">|</span> <span class="token punctuation">[</span><span class="token keyword">CONSTRAINT</span> <span class="token punctuation">[</span><em class="replaceable">symbol</em><span class="token punctuation">]</span><span class="token punctuation">]</span> <span class="token keyword">FOREIGN</span> <span class="token keyword">KEY</span>
<span class="token punctuation">[</span><em class="replaceable">index_name</em><span class="token punctuation">]</span> <span class="token punctuation">(</span><em class="replaceable">col_name</em><span class="token punctuation">,</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">)</span>
<em class="replaceable">reference_definition</em>
<span class="token operator">|</span> <em class="replaceable">check_constraint_definition</em>
}
<em class="replaceable">column_definition</em>: {
<em class="replaceable">data_type</em> <span class="token punctuation">[</span><span class="token operator">NOT</span> <span class="token boolean">NULL</span> <span class="token operator">|</span> <span class="token boolean">NULL</span><span class="token punctuation">]</span> <span class="token punctuation">[</span><span class="token keyword">DEFAULT</span> {<em class="replaceable">literal</em> <span class="token operator">|</span> <span class="token punctuation">(</span><em class="replaceable">expr</em><span class="token punctuation">)</span>} <span class="token punctuation">]</span>
<span class="token punctuation">[</span><span class="token keyword">VISIBLE</span> <span class="token operator">|</span> <span class="token keyword">INVISIBLE</span><span class="token punctuation">]</span>
<span class="token punctuation">[</span><span class="token keyword">AUTO_INCREMENT</span><span class="token punctuation">]</span> <span class="token punctuation">[</span><span class="token keyword">UNIQUE</span> <span class="token punctuation">[</span><span class="token keyword">KEY</span><span class="token punctuation">]</span><span class="token punctuation">]</span> <span class="token punctuation">[</span><span class="token punctuation">[</span><span class="token keyword">PRIMARY</span><span class="token punctuation">]</span> <span class="token keyword">KEY</span><span class="token punctuation">]</span>
<span class="token punctuation">[</span><span class="token keyword">COMMENT</span> <span class="token string">'<em class="replaceable">string</em>'</span><span class="token punctuation">]</span>
<span class="token punctuation">[</span><span class="token keyword">COLLATE</span> <em class="replaceable">collation_name</em><span class="token punctuation">]</span>
<span class="token punctuation">[</span><span class="token keyword">COLUMN_FORMAT</span> {<span class="token keyword">FIXED</span> <span class="token operator">|</span> <span class="token keyword">DYNAMIC</span> <span class="token operator">|</span> <span class="token keyword">DEFAULT</span>}<span class="token punctuation">]</span>
<span class="token punctuation">[</span><span class="token keyword">ENGINE_ATTRIBUTE</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> <span class="token string">'<em class="replaceable">string</em>'</span><span class="token punctuation">]</span>
<span class="token punctuation">[</span><span class="token keyword">SECONDARY_ENGINE_ATTRIBUTE</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> <span class="token string">'<em class="replaceable">string</em>'</span><span class="token punctuation">]</span>
<span class="token punctuation">[</span><span class="token keyword">STORAGE</span> {<span class="token keyword">DISK</span> <span class="token operator">|</span> <span class="token keyword">MEMORY</span>}<span class="token punctuation">]</span>
<span class="token punctuation">[</span><em class="replaceable">reference_definition</em><span class="token punctuation">]</span>
<span class="token punctuation">[</span><em class="replaceable">check_constraint_definition</em><span class="token punctuation">]</span>
<span class="token operator">|</span> <em class="replaceable">data_type</em>
<span class="token punctuation">[</span><span class="token keyword">COLLATE</span> <em class="replaceable">collation_name</em><span class="token punctuation">]</span>
<span class="token punctuation">[</span><span class="token keyword">GENERATED</span> <span class="token keyword">ALWAYS</span><span class="token punctuation">]</span> <span class="token keyword">AS</span> <span class="token punctuation">(</span><em class="replaceable">expr</em><span class="token punctuation">)</span>
<span class="token punctuation">[</span><span class="token keyword">VIRTUAL</span> <span class="token operator">|</span> <span class="token keyword">STORED</span><span class="token punctuation">]</span> <span class="token punctuation">[</span><span class="token operator">NOT</span> <span class="token boolean">NULL</span> <span class="token operator">|</span> <span class="token boolean">NULL</span><span class="token punctuation">]</span>
<span class="token punctuation">[</span><span class="token keyword">VISIBLE</span> <span class="token operator">|</span> <span class="token keyword">INVISIBLE</span><span class="token punctuation">]</span>
<span class="token punctuation">[</span><span class="token keyword">UNIQUE</span> <span class="token punctuation">[</span><span class="token keyword">KEY</span><span class="token punctuation">]</span><span class="token punctuation">]</span> <span class="token punctuation">[</span><span class="token punctuation">[</span><span class="token keyword">PRIMARY</span><span class="token punctuation">]</span> <span class="token keyword">KEY</span><span class="token punctuation">]</span>
<span class="token punctuation">[</span><span class="token keyword">COMMENT</span> <span class="token string">'<em class="replaceable">string</em>'</span><span class="token punctuation">]</span>
<span class="token punctuation">[</span><em class="replaceable">reference_definition</em><span class="token punctuation">]</span>
<span class="token punctuation">[</span><em class="replaceable">check_constraint_definition</em><span class="token punctuation">]</span>
}
<em class="replaceable">data_type</em>:
<span class="token punctuation">(</span>see Chapter <span class="token number">13</span><span class="token punctuation">,</span> <span class="token keyword">Data</span> <span class="token keyword">Types</span><span class="token punctuation">)</span>
<em class="replaceable">key_part</em>: {<em class="replaceable">col_name</em> <span class="token punctuation">[</span><span class="token punctuation">(</span><em class="replaceable">length</em><span class="token punctuation">)</span><span class="token punctuation">]</span> <span class="token operator">|</span> <span class="token punctuation">(</span><em class="replaceable">expr</em><span class="token punctuation">)</span>} <span class="token punctuation">[</span><span class="token keyword">ASC</span> <span class="token operator">|</span> <span class="token keyword">DESC</span><span class="token punctuation">]</span>
<em class="replaceable">index_type</em>:
<span class="token keyword">USING</span> {<span class="token keyword">BTREE</span> <span class="token operator">|</span> <span class="token keyword">HASH</span>}
<em class="replaceable">index_option</em>: {
<span class="token keyword">KEY_BLOCK_SIZE</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> <span class="token keyword"><em class="replaceable">value</em></span>
<span class="token operator">|</span> <em class="replaceable">index_type</em>
<span class="token operator">|</span> <span class="token keyword">WITH</span> <span class="token keyword">PARSER</span> <em class="replaceable">parser_name</em>
<span class="token operator">|</span> <span class="token keyword">COMMENT</span> <span class="token string">'<em class="replaceable">string</em>'</span>
<span class="token operator">|</span> {<span class="token keyword">VISIBLE</span> <span class="token operator">|</span> <span class="token keyword">INVISIBLE</span>}
<span class="token operator">|</span><span class="token keyword">ENGINE_ATTRIBUTE</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> <span class="token string">'<em class="replaceable">string</em>'</span>
<span class="token operator">|</span><span class="token keyword">SECONDARY_ENGINE_ATTRIBUTE</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> <span class="token string">'<em class="replaceable">string</em>'</span>
}
<em class="replaceable">check_constraint_definition</em>:
<span class="token punctuation">[</span><span class="token keyword">CONSTRAINT</span> <span class="token punctuation">[</span><em class="replaceable">symbol</em><span class="token punctuation">]</span><span class="token punctuation">]</span> <span class="token keyword">CHECK</span> <span class="token punctuation">(</span><em class="replaceable">expr</em><span class="token punctuation">)</span> <span class="token punctuation">[</span><span class="token punctuation">[</span><span class="token operator">NOT</span><span class="token punctuation">]</span> <span class="token keyword">ENFORCED</span><span class="token punctuation">]</span>
<em class="replaceable">reference_definition</em>:
<span class="token keyword">REFERENCES</span> <em class="replaceable">tbl_name</em> <span class="token punctuation">(</span><em class="replaceable">key_part</em><span class="token punctuation">,</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">)</span>
<span class="token punctuation">[</span><span class="token operator">MATCH</span> <span class="token keyword">FULL</span> <span class="token operator">|</span> <span class="token operator">MATCH</span> <span class="token keyword">PARTIAL</span> <span class="token operator">|</span> <span class="token operator">MATCH</span> <span class="token keyword">SIMPLE</span><span class="token punctuation">]</span>
<span class="token punctuation">[</span><span class="token keyword">ON</span> <span class="token keyword">DELETE</span> <em class="replaceable">reference_option</em><span class="token punctuation">]</span>
<span class="token punctuation">[</span><span class="token keyword">ON</span> <span class="token keyword">UPDATE</span> <em class="replaceable">reference_option</em><span class="token punctuation">]</span>
<em class="replaceable">reference_option</em>:
<span class="token keyword">RESTRICT</span> <span class="token operator">|</span> <span class="token keyword">CASCADE</span> <span class="token operator">|</span> <span class="token keyword">SET</span> <span class="token boolean">NULL</span> <span class="token operator">|</span> <span class="token keyword">NO</span> <span class="token keyword">ACTION</span> <span class="token operator">|</span> <span class="token keyword">SET</span> <span class="token keyword">DEFAULT</span>
<em class="replaceable">table_options</em>:
<em class="replaceable">table_option</em> <span class="token punctuation">[</span><span class="token punctuation">[</span><span class="token punctuation">,</span><span class="token punctuation">]</span> <em class="replaceable">table_option</em><span class="token punctuation">]</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<em class="replaceable">table_option</em>: {
<span class="token keyword">AUTOEXTEND_SIZE</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> <span class="token keyword"><em class="replaceable">value</em></span>
<span class="token operator">|</span> <span class="token keyword">AUTO_INCREMENT</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> <span class="token keyword"><em class="replaceable">value</em></span>
<span class="token operator">|</span> <span class="token keyword">AVG_ROW_LENGTH</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> <span class="token keyword"><em class="replaceable">value</em></span>
<span class="token operator">|</span> <span class="token punctuation">[</span><span class="token keyword">DEFAULT</span><span class="token punctuation">]</span> <span class="token keyword">CHARACTER</span> <span class="token keyword">SET</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> <em class="replaceable">charset_name</em>
<span class="token operator">|</span> <span class="token keyword">CHECKSUM</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> {<span class="token number">0</span> <span class="token operator">|</span> <span class="token number">1</span>}
<span class="token operator">|</span> <span class="token punctuation">[</span><span class="token keyword">DEFAULT</span><span class="token punctuation">]</span> <span class="token keyword">COLLATE</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> <em class="replaceable">collation_name</em>
<span class="token operator">|</span> <span class="token keyword">COMMENT</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> <span class="token string">'<em class="replaceable">string</em>'</span>
<span class="token operator">|</span> <span class="token keyword">COMPRESSION</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> {<span class="token string">'ZLIB'</span> <span class="token operator">|</span> <span class="token string">'LZ4'</span> <span class="token operator">|</span> <span class="token string">'NONE'</span>}
<span class="token operator">|</span> <span class="token keyword">CONNECTION</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> <span class="token string">'<em class="replaceable">connect_string</em>'</span>
<span class="token operator">|</span> {<span class="token keyword">DATA</span> <span class="token operator">|</span> <span class="token keyword">INDEX</span>} <span class="token keyword">DIRECTORY</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> <span class="token string">'<em class="replaceable">absolute path to directory</em>'</span>
<span class="token operator">|</span> <span class="token keyword">DELAY_KEY_WRITE</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> {<span class="token number">0</span> <span class="token operator">|</span> <span class="token number">1</span>}
<span class="token operator">|</span> <span class="token keyword">ENCRYPTION</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> {<span class="token string">'Y'</span> <span class="token operator">|</span> <span class="token string">'N'</span>}
<span class="token operator">|</span> <span class="token keyword">ENGINE</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> <em class="replaceable">engine_name</em>
<span class="token operator">|</span> <span class="token keyword">ENGINE_ATTRIBUTE</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> <span class="token string">'<em class="replaceable">string</em>'</span>
<span class="token operator">|</span> <span class="token keyword">INSERT_METHOD</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> { <span class="token keyword">NO</span> <span class="token operator">|</span> <span class="token keyword">FIRST</span> <span class="token operator">|</span> <span class="token keyword">LAST</span> }
<span class="token operator">|</span> <span class="token keyword">KEY_BLOCK_SIZE</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> <span class="token keyword"><em class="replaceable">value</em></span>
<span class="token operator">|</span> <span class="token keyword">MAX_ROWS</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> <span class="token keyword"><em class="replaceable">value</em></span>
<span class="token operator">|</span> <span class="token keyword">MIN_ROWS</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> <span class="token keyword"><em class="replaceable">value</em></span>
<span class="token operator">|</span> <span class="token keyword">PACK_KEYS</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> {<span class="token number">0</span> <span class="token operator">|</span> <span class="token number">1</span> <span class="token operator">|</span> <span class="token keyword">DEFAULT</span>}
<span class="token operator">|</span> <span class="token keyword">PASSWORD</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> <span class="token string">'<em class="replaceable">string</em>'</span>
<span class="token operator">|</span> <span class="token keyword">ROW_FORMAT</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> {<span class="token keyword">DEFAULT</span> <span class="token operator">|</span> <span class="token keyword">DYNAMIC</span> <span class="token operator">|</span> <span class="token keyword">FIXED</span> <span class="token operator">|</span> <span class="token keyword">COMPRESSED</span> <span class="token operator">|</span> <span class="token keyword">REDUNDANT</span> <span class="token operator">|</span> <span class="token keyword">COMPACT</span>}
<span class="token operator">|</span> <span class="token keyword">START</span> <span class="token keyword">TRANSACTION</span>
<span class="token operator">|</span> <span class="token keyword">SECONDARY_ENGINE_ATTRIBUTE</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> <span class="token string">'<em class="replaceable">string</em>'</span>
<span class="token operator">|</span> <span class="token keyword">STATS_AUTO_RECALC</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> {<span class="token keyword">DEFAULT</span> <span class="token operator">|</span> <span class="token number">0</span> <span class="token operator">|</span> <span class="token number">1</span>}
<span class="token operator">|</span> <span class="token keyword">STATS_PERSISTENT</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> {<span class="token keyword">DEFAULT</span> <span class="token operator">|</span> <span class="token number">0</span> <span class="token operator">|</span> <span class="token number">1</span>}
<span class="token operator">|</span> <span class="token keyword">STATS_SAMPLE_PAGES</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> <span class="token keyword"><em class="replaceable">value</em></span>
<span class="token operator">|</span> <em class="replaceable">tablespace_option</em>
<span class="token operator">|</span> <span class="token keyword">UNION</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> <span class="token punctuation">(</span><em class="replaceable">tbl_name</em><span class="token punctuation">[</span><span class="token punctuation">,</span><em class="replaceable">tbl_name</em><span class="token punctuation">]</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">)</span>
}
<em class="replaceable">partition_options</em>:
<span class="token keyword">PARTITION</span> <span class="token keyword">BY</span>
{ <span class="token punctuation">[</span><span class="token keyword">LINEAR</span><span class="token punctuation">]</span> <span class="token keyword">HASH</span><span class="token punctuation">(</span><em class="replaceable">expr</em><span class="token punctuation">)</span>
<span class="token operator">|</span> <span class="token punctuation">[</span><span class="token keyword">LINEAR</span><span class="token punctuation">]</span> <span class="token keyword">KEY</span> <span class="token punctuation">[</span><span class="token keyword">ALGORITHM</span><span class="token operator">=</span>{<span class="token number">1</span> <span class="token operator">|</span> <span class="token number">2</span>}<span class="token punctuation">]</span> <span class="token punctuation">(</span><em class="replaceable">column_list</em><span class="token punctuation">)</span>
<span class="token operator">|</span> <span class="token keyword">RANGE</span>{<span class="token punctuation">(</span><em class="replaceable">expr</em><span class="token punctuation">)</span> <span class="token operator">|</span> <span class="token keyword">COLUMNS</span><span class="token punctuation">(</span><em class="replaceable">column_list</em><span class="token punctuation">)</span>}
<span class="token operator">|</span> <span class="token keyword">LIST</span>{<span class="token punctuation">(</span><em class="replaceable">expr</em><span class="token punctuation">)</span> <span class="token operator">|</span> <span class="token keyword">COLUMNS</span><span class="token punctuation">(</span><em class="replaceable">column_list</em><span class="token punctuation">)</span>} }
<span class="token punctuation">[</span><span class="token keyword">PARTITIONS</span> <em class="replaceable">num</em><span class="token punctuation">]</span>
<span class="token punctuation">[</span><span class="token keyword">SUBPARTITION</span> <span class="token keyword">BY</span>
{ <span class="token punctuation">[</span><span class="token keyword">LINEAR</span><span class="token punctuation">]</span> <span class="token keyword">HASH</span><span class="token punctuation">(</span><em class="replaceable">expr</em><span class="token punctuation">)</span>
<span class="token operator">|</span> <span class="token punctuation">[</span><span class="token keyword">LINEAR</span><span class="token punctuation">]</span> <span class="token keyword">KEY</span> <span class="token punctuation">[</span><span class="token keyword">ALGORITHM</span><span class="token operator">=</span>{<span class="token number">1</span> <span class="token operator">|</span> <span class="token number">2</span>}<span class="token punctuation">]</span> <span class="token punctuation">(</span><em class="replaceable">column_list</em><span class="token punctuation">)</span> }
<span class="token punctuation">[</span><span class="token keyword">SUBPARTITIONS</span> <em class="replaceable">num</em><span class="token punctuation">]</span>
<span class="token punctuation">]</span>
<span class="token punctuation">[</span><span class="token punctuation">(</span><em class="replaceable">partition_definition</em> <span class="token punctuation">[</span><span class="token punctuation">,</span> <em class="replaceable">partition_definition</em><span class="token punctuation">]</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">)</span><span class="token punctuation">]</span>
<em class="replaceable">partition_definition</em>:
<span class="token keyword">PARTITION</span> <em class="replaceable">partition_name</em>
<span class="token punctuation">[</span><span class="token keyword">VALUES</span>
{<span class="token keyword">LESS</span> <span class="token keyword">THAN</span> {<span class="token punctuation">(</span><em class="replaceable">expr</em> <span class="token operator">|</span> <em class="replaceable">value_list</em><span class="token punctuation">)</span> <span class="token operator">|</span> <span class="token keyword">MAXVALUE</span>}
<span class="token operator">|</span>
<span class="token keyword">IN</span> <span class="token punctuation">(</span><em class="replaceable">value_list</em><span class="token punctuation">)</span>}<span class="token punctuation">]</span>
<span class="token punctuation">[</span><span class="token punctuation">[</span><span class="token keyword">STORAGE</span><span class="token punctuation">]</span> <span class="token keyword">ENGINE</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> <em class="replaceable">engine_name</em><span class="token punctuation">]</span>
<span class="token punctuation">[</span><span class="token keyword">COMMENT</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> <span class="token string">'<em class="replaceable">string</em>'</span> <span class="token punctuation">]</span>
<span class="token punctuation">[</span><span class="token keyword">DATA</span> <span class="token keyword">DIRECTORY</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> <span class="token string">'<em class="replaceable">data_dir</em>'</span><span class="token punctuation">]</span>
<span class="token punctuation">[</span><span class="token keyword">INDEX</span> <span class="token keyword">DIRECTORY</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> <span class="token string">'<em class="replaceable">index_dir</em>'</span><span class="token punctuation">]</span>
<span class="token punctuation">[</span><span class="token keyword">MAX_ROWS</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> <em class="replaceable">max_number_of_rows</em><span class="token punctuation">]</span>
<span class="token punctuation">[</span><span class="token keyword">MIN_ROWS</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> <em class="replaceable">min_number_of_rows</em><span class="token punctuation">]</span>
<span class="token punctuation">[</span><span class="token keyword">TABLESPACE</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> tablespace_name<span class="token punctuation">]</span>
<span class="token punctuation">[</span><span class="token punctuation">(</span><em class="replaceable">subpartition_definition</em> <span class="token punctuation">[</span><span class="token punctuation">,</span> <em class="replaceable">subpartition_definition</em><span class="token punctuation">]</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">)</span><span class="token punctuation">]</span>
<em class="replaceable">subpartition_definition</em>:
<span class="token keyword">SUBPARTITION</span> <em class="replaceable">logical_name</em>
<span class="token punctuation">[</span><span class="token punctuation">[</span><span class="token keyword">STORAGE</span><span class="token punctuation">]</span> <span class="token keyword">ENGINE</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> <em class="replaceable">engine_name</em><span class="token punctuation">]</span>
<span class="token punctuation">[</span><span class="token keyword">COMMENT</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> <span class="token string">'<em class="replaceable">string</em>'</span> <span class="token punctuation">]</span>
<span class="token punctuation">[</span><span class="token keyword">DATA</span> <span class="token keyword">DIRECTORY</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> <span class="token string">'<em class="replaceable">data_dir</em>'</span><span class="token punctuation">]</span>
<span class="token punctuation">[</span><span class="token keyword">INDEX</span> <span class="token keyword">DIRECTORY</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> <span class="token string">'<em class="replaceable">index_dir</em>'</span><span class="token punctuation">]</span>
<span class="token punctuation">[</span><span class="token keyword">MAX_ROWS</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> <em class="replaceable">max_number_of_rows</em><span class="token punctuation">]</span>
<span class="token punctuation">[</span><span class="token keyword">MIN_ROWS</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> <em class="replaceable">min_number_of_rows</em><span class="token punctuation">]</span>
<span class="token punctuation">[</span><span class="token keyword">TABLESPACE</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> tablespace_name<span class="token punctuation">]</span>
<em class="replaceable">tablespace_option</em>:
<span class="token keyword">TABLESPACE</span> <em class="replaceable">tablespace_name</em> <span class="token punctuation">[</span><span class="token keyword">STORAGE</span> <span class="token keyword">DISK</span><span class="token punctuation">]</span>
<span class="token operator">|</span> <span class="token punctuation">[</span><span class="token keyword">TABLESPACE</span> <em class="replaceable">tablespace_name</em><span class="token punctuation">]</span> <span class="token keyword">STORAGE</span> <span class="token keyword">MEMORY</span>
<em class="replaceable">query_expression:</em>
<span class="token keyword">SELECT</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span> <span class="token punctuation">(</span><span class="token keyword"></span><em class="replaceable"><span class="token keyword">Some</span> valid <span class="token keyword">select</span> <span class="token operator">or</span> <span class="token keyword">union</span> statement</em><span class="token punctuation">)</span></code></pre>
</div>
<p>
<a class="link" href="create-table.html" title="15.1.20 CREATE TABLE Statement">
<code class="literal">
CREATE TABLE
</code>
</a>
creates a table with
the given name. You must have the
<a class="link" href="privileges-provided.html#priv_create">
<code class="literal">
CREATE
</code>
</a>
privilege for the table.
</p>
<p>
By default, tables are created in the default database, using the
<a class="link" href="innodb-storage-engine.html" title="Chapter 17 The InnoDB Storage Engine">
<code class="literal">
InnoDB
</code>
</a>
storage engine. An error
occurs if the table exists, if there is no default database, or if
the database does not exist.
</p>
<a class="indexterm" name="idm46045186561072">
</a>
<a class="indexterm" name="idm46045186559568">
</a>
<p>
MySQL has no limit on the number of tables. The underlying file
system may have a limit on the number of files that represent
tables. Individual storage engines may impose engine-specific
constraints.
<code class="literal">
InnoDB
</code>
permits up to 4 billion
tables.
</p>
<p>
For information about the physical representation of a table, see
<a class="xref" href="create-table-files.html" title="15.1.20.1 Files Created by CREATE TABLE">
Section 15.1.20.1, “Files Created by CREATE TABLE”
</a>
.
</p>
<p>
There are several aspects to the
<a class="link" href="create-table.html" title="15.1.20 CREATE TABLE Statement">
<code class="literal">
CREATE
TABLE
</code>
</a>
statement, described under the following topics in
this section:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<a class="xref" href="create-table.html#create-table-name" title="Table Name">
Table Name
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="create-table.html#create-table-temporary-tables" title="Temporary Tables">
Temporary Tables
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="create-table.html#create-table-clone-copy" title="Table Cloning and Copying">
Table Cloning and Copying
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="create-table.html#create-table-types-attributes" title="Column Data Types and Attributes">
Column Data Types and Attributes
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="create-table.html#create-table-indexes-keys" title="Indexes, Foreign Keys, and CHECK Constraints">
Indexes, Foreign Keys, and CHECK Constraints
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="create-table.html#create-table-options" title="Table Options">
Table Options
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="create-table.html#create-table-partitioning" title="Table Partitioning">
Table Partitioning
</a>
</p>
</li>
</ul>
</div>
<h4>
<a name="create-table-name">
</a>
Table Name
</h4>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<code class="literal">
<em class="replaceable">
<code>
tbl_name
</code>
</em>
</code>
</p>
<p>
The table name can be specified as
<em class="replaceable">
<code>
db_name.tbl_name
</code>
</em>
to create the
table in a specific database. This works regardless of whether
there is a default database, assuming that the database
exists. If you use quoted identifiers, quote the database and
table names separately. For example, write
<code class="literal">
`mydb`.`mytbl`
</code>
, not
<code class="literal">
`mydb.mytbl`
</code>
.
</p>
<p>
Rules for permissible table names are given in
<a class="xref" href="identifiers.html" title="11.2 Schema Object Names">
Section 11.2, “Schema Object Names”
</a>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
IF NOT EXISTS
</code>
</p>
<p>
Prevents an error from occurring if the table exists. However,
there is no verification that the existing table has a
structure identical to that indicated by the
<a class="link" href="create-table.html" title="15.1.20 CREATE TABLE Statement">
<code class="literal">
CREATE TABLE
</code>
</a>
statement.
</p>
</li>
</ul>
</div>
<h4>
<a name="create-table-temporary-tables">
</a>
Temporary Tables
</h4>
<p>
You can use the
<code class="literal">
TEMPORARY
</code>
keyword when creating
a table. A
<code class="literal">
TEMPORARY
</code>
table is visible only
within the current session, and is dropped automatically when the
session is closed. For more information, see
<a class="xref" href="create-temporary-table.html" title="15.1.20.2 CREATE TEMPORARY TABLE Statement">
Section 15.1.20.2, “CREATE TEMPORARY TABLE Statement”
</a>
.
</p>
<h4>
<a name="create-table-clone-copy">
</a>
Table Cloning and Copying
</h4>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<code class="literal">
LIKE
</code>
</p>
<p>
Use
<code class="literal">
CREATE TABLE ... LIKE
</code>
to create an
empty table based on the definition of another table,
including any column attributes and indexes defined in the
original table:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa12918098"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> <em class="replaceable">new_tbl</em> <span class="token operator">LIKE</span> <em class="replaceable">orig_tbl</em><span class="token punctuation">;</span></code></pre>
</div>
<p>
For more information, see
<a class="xref" href="create-table-like.html" title="15.1.20.3 CREATE TABLE ... LIKE Statement">
Section 15.1.20.3, “CREATE TABLE ... LIKE Statement”
</a>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
[AS]
<em class="replaceable">
<code>
query_expression
</code>
</em>
</code>
</p>
<p>
To create one table from another, add a
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT
</code>
</a>
statement at the end of
the
<a class="link" href="create-table.html" title="15.1.20 CREATE TABLE Statement">
<code class="literal">
CREATE TABLE
</code>
</a>
statement:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa11989747"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> <em class="replaceable">new_tbl</em> <span class="token keyword">AS</span> <span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> <em class="replaceable">orig_tbl</em><span class="token punctuation">;</span></code></pre>
</div>
<p>
For more information, see
<a class="xref" href="create-table-select.html" title="15.1.20.4 CREATE TABLE ... SELECT Statement">
Section 15.1.20.4, “CREATE TABLE ... SELECT Statement”
</a>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
IGNORE | REPLACE
</code>
</p>
<p>
The
<code class="literal">
IGNORE
</code>
and
<code class="literal">
REPLACE
</code>
options indicate how to handle rows that duplicate unique key
values when copying a table using a
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT
</code>
</a>
statement.
</p>
<p>
For more information, see
<a class="xref" href="create-table-select.html" title="15.1.20.4 CREATE TABLE ... SELECT Statement">
Section 15.1.20.4, “CREATE TABLE ... SELECT Statement”
</a>
.
</p>
</li>
</ul>
</div>
<h4>
<a name="create-table-types-attributes">
</a>
Column Data Types and Attributes
</h4>
<p>
There is a hard limit of 4096 columns per table, but the effective
maximum may be less for a given table and depends on the factors
discussed in
<a class="xref" href="column-count-limit.html" title="10.4.7 Limits on Table Column Count and Row Size">
Section 10.4.7, “Limits on Table Column Count and Row Size”
</a>
.
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<code class="literal">
<em class="replaceable">
<code>
data_type
</code>
</em>
</code>
</p>
<p>
<em class="replaceable">
<code>
data_type
</code>
</em>
represents the data type
in a column definition. For a full description of the syntax
available for specifying column data types, as well as
information about the properties of each type, see
<a class="xref" href="data-types.html" title="Chapter 13 Data Types">
Chapter 13,
<i>
Data Types
</i>
</a>
.
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<p>
<code class="literal">
AUTO_INCREMENT
</code>
applies only to integer
types.
</p>
</li>
<li class="listitem">
<p>
Character data types (
<a class="link" href="char.html" title="13.3.2 The CHAR and VARCHAR Types">
<code class="literal">
CHAR
</code>
</a>
,
<a class="link" href="char.html" title="13.3.2 The CHAR and VARCHAR Types">
<code class="literal">
VARCHAR
</code>
</a>
, the
<a class="link" href="blob.html" title="13.3.4 The BLOB and TEXT Types">
<code class="literal">
TEXT
</code>
</a>
types,
<a class="link" href="enum.html" title="13.3.5 The ENUM Type">
<code class="literal">
ENUM
</code>
</a>
,
<a class="link" href="set.html" title="13.3.6 The SET Type">
<code class="literal">
SET
</code>
</a>
, and any synonyms) can
include
<code class="literal">
CHARACTER SET
</code>
to specify the
character set for the column.
<code class="literal">
CHARSET
</code>
is a synonym for
<code class="literal">
CHARACTER SET
</code>
. A
collation for the character set can be specified with the
<code class="literal">
COLLATE
</code>
attribute, along with any other
attributes. For details, see
<a class="xref" href="charset.html" title="Chapter 12 Character Sets, Collations, Unicode">
Chapter 12,
<i>
Character Sets, Collations, Unicode
</i>
</a>
.
Example:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa84979021"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> t <span class="token punctuation">(</span>c <span class="token datatype">CHAR</span><span class="token punctuation">(</span><span class="token number">20</span><span class="token punctuation">)</span> <span class="token keyword">CHARACTER</span> <span class="token keyword">SET</span> utf8mb4 <span class="token keyword">COLLATE</span> utf8mb4_bin<span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
MySQL 8.4 interprets length specifications in
character column definitions in characters. Lengths for
<a class="link" href="binary-varbinary.html" title="13.3.3 The BINARY and VARBINARY Types">
<code class="literal">
BINARY
</code>
</a>
and
<a class="link" href="binary-varbinary.html" title="13.3.3 The BINARY and VARBINARY Types">
<code class="literal">
VARBINARY
</code>
</a>
are in bytes.
</p>
</li>
<li class="listitem">
<p>
For
<a class="link" href="char.html" title="13.3.2 The CHAR and VARCHAR Types">
<code class="literal">
CHAR
</code>
</a>
,
<a class="link" href="char.html" title="13.3.2 The CHAR and VARCHAR Types">
<code class="literal">
VARCHAR
</code>
</a>
,
<a class="link" href="binary-varbinary.html" title="13.3.3 The BINARY and VARBINARY Types">
<code class="literal">
BINARY
</code>
</a>
, and
<a class="link" href="binary-varbinary.html" title="13.3.3 The BINARY and VARBINARY Types">
<code class="literal">
VARBINARY
</code>
</a>
columns, indexes
can be created that use only the leading part of column
values, using
<code class="literal">
<em class="replaceable">
<code>
col_name
</code>
</em>
(
<em class="replaceable">
<code>
length
</code>
</em>
)
</code>
syntax to specify an index prefix length.
<a class="link" href="blob.html" title="13.3.4 The BLOB and TEXT Types">
<code class="literal">
BLOB
</code>
</a>
and
<a class="link" href="blob.html" title="13.3.4 The BLOB and TEXT Types">
<code class="literal">
TEXT
</code>
</a>
columns also can be
indexed, but a prefix length
<span class="emphasis">
<em>
must
</em>
</span>
be
given. Prefix lengths are given in characters for
nonbinary string types and in bytes for binary string
types. That is, index entries consist of the first
<em class="replaceable">
<code>
length
</code>
</em>
characters of each
column value for
<a class="link" href="char.html" title="13.3.2 The CHAR and VARCHAR Types">
<code class="literal">
CHAR
</code>
</a>
,
<a class="link" href="char.html" title="13.3.2 The CHAR and VARCHAR Types">
<code class="literal">
VARCHAR
</code>
</a>
, and
<a class="link" href="blob.html" title="13.3.4 The BLOB and TEXT Types">
<code class="literal">
TEXT
</code>
</a>
columns, and the first
<em class="replaceable">
<code>
length
</code>
</em>
bytes of each column
value for
<a class="link" href="binary-varbinary.html" title="13.3.3 The BINARY and VARBINARY Types">
<code class="literal">
BINARY
</code>
</a>
,
<a class="link" href="binary-varbinary.html" title="13.3.3 The BINARY and VARBINARY Types">
<code class="literal">
VARBINARY
</code>
</a>
, and
<a class="link" href="blob.html" title="13.3.4 The BLOB and TEXT Types">
<code class="literal">
BLOB
</code>
</a>
columns. Indexing only
a prefix of column values like this can make the index
file much smaller. For additional information about index
prefixes, see
<a class="xref" href="create-index.html" title="15.1.15 CREATE INDEX Statement">
Section 15.1.15, “CREATE INDEX Statement”
</a>
.
</p>
<a class="indexterm" name="idm46045186468928">
</a>
<a class="indexterm" name="idm46045186467440">
</a>
<a class="indexterm" name="idm46045186465952">
</a>
<a class="indexterm" name="idm46045186464464">
</a>
<p>
Only the
<code class="literal">
InnoDB
</code>
and
<code class="literal">
MyISAM
</code>
storage engines support indexing
on
<a class="link" href="blob.html" title="13.3.4 The BLOB and TEXT Types">
<code class="literal">
BLOB
</code>
</a>
and
<a class="link" href="blob.html" title="13.3.4 The BLOB and TEXT Types">
<code class="literal">
TEXT
</code>
</a>
columns. For example:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa22760630"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> test <span class="token punctuation">(</span>blob_col <span class="token datatype">BLOB</span><span class="token punctuation">,</span> <span class="token keyword">INDEX</span><span class="token punctuation">(</span>blob_col<span class="token punctuation">(</span><span class="token number">10</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
If a specified index prefix exceeds the maximum column
data type size,
<a class="link" href="create-table.html" title="15.1.20 CREATE TABLE Statement">
<code class="literal">
CREATE
TABLE
</code>
</a>
handles the index as follows:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: square; ">
<li class="listitem">
<p>
For a nonunique index, either an error occurs (if
strict SQL mode is enabled), or the index length is
reduced to lie within the maximum column data type
size and a warning is produced (if strict SQL mode is
not enabled).
</p>
</li>
<li class="listitem">
<p>
For a unique index, an error occurs regardless of SQL
mode because reducing the index length might enable
insertion of nonunique entries that do not meet the
specified uniqueness requirement.
</p>
</li>
</ul>
</div>
</li>
<li class="listitem">
<p>
<a class="link" href="json.html" title="13.5 The JSON Data Type">
<code class="literal">
JSON
</code>
</a>
columns cannot be
indexed. You can work around this restriction by creating
an index on a generated column that extracts a scalar
value from the
<code class="literal">
JSON
</code>
column. See
<a class="xref" href="create-table-secondary-indexes.html#json-column-indirect-index" title="Indexing a Generated Column to Provide a JSON Column Index">
Indexing a Generated Column to Provide a JSON Column Index
</a>
, for a
detailed example.
</p>
</li>
</ul>
</div>
</li>
<li class="listitem">
<p>
<code class="literal">
NOT NULL | NULL
</code>
</p>
<a class="indexterm" name="idm46045186447856">
</a>
<a class="indexterm" name="idm46045186446368">
</a>
<p>
If neither
<code class="literal">
NULL
</code>
nor
<code class="literal">
NOT
NULL
</code>
is specified, the column is treated as though
<code class="literal">
NULL
</code>
had been specified.
</p>
<p>
In MySQL 8.4, only the
<code class="literal">
InnoDB
</code>
,
<code class="literal">
MyISAM
</code>
, and
<code class="literal">
MEMORY
</code>
storage engines support indexes on columns that can have
<code class="literal">
NULL
</code>
values. In other cases, you must
declare indexed columns as
<code class="literal">
NOT NULL
</code>
or an
error results.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
DEFAULT
</code>
</p>
<a class="indexterm" name="idm46045186436656">
</a>
<a class="indexterm" name="idm46045186435584">
</a>
<p>
Specifies a default value for a column. For more information
about default value handling, including the case that a column
definition includes no explicit
<code class="literal">
DEFAULT
</code>
value, see
<a class="xref" href="data-type-defaults.html" title="13.6 Data Type Default Values">
Section 13.6, “Data Type Default Values”
</a>
.
</p>
<p>
If the
<a class="link" href="sql-mode.html#sqlmode_no_zero_date">
<code class="literal">
NO_ZERO_DATE
</code>
</a>
or
<a class="link" href="sql-mode.html#sqlmode_no_zero_in_date">
<code class="literal">
NO_ZERO_IN_DATE
</code>
</a>
SQL mode is
enabled and a date-valued default is not correct according to
that mode,
<a class="link" href="create-table.html" title="15.1.20 CREATE TABLE Statement">
<code class="literal">
CREATE TABLE
</code>
</a>
produces a warning if strict SQL mode is not enabled and an
error if strict mode is enabled. For example, with
<a class="link" href="sql-mode.html#sqlmode_no_zero_in_date">
<code class="literal">
NO_ZERO_IN_DATE
</code>
</a>
enabled,
<code class="literal">
c1 DATE DEFAULT '2010-00-00'
</code>
produces a
warning.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
VISIBLE
</code>
,
<code class="literal">
INVISIBLE
</code>
</p>
<p>
Specify column visibility. The default is
<code class="literal">
VISIBLE
</code>
if neither keyword is present. A
table must have at least one visible column. Attempting to
make all columns invisible produces an error. For more
information, see
<a class="xref" href="invisible-columns.html" title="15.1.20.10 Invisible Columns">
Section 15.1.20.10, “Invisible Columns”
</a>
.
</p>
<a class="indexterm" name="idm46045186422032">
</a>
</li>
<li class="listitem">
<p>
<code class="literal">
AUTO_INCREMENT
</code>
</p>
<p>
An integer column can have the additional attribute
<code class="literal">
AUTO_INCREMENT
</code>
. When you insert a value of
<code class="literal">
NULL
</code>
(recommended) or
<code class="literal">
0
</code>
into an indexed
<code class="literal">
AUTO_INCREMENT
</code>
column, the
column is set to the next sequence value. Typically this is
<code class="literal">
<em class="replaceable">
<code>
value
</code>
</em>
+1
</code>
, where
<em class="replaceable">
<code>
value
</code>
</em>
is the largest value for the
column currently in the table.
<code class="literal">
AUTO_INCREMENT
</code>
sequences begin with
<code class="literal">
1
</code>
.
</p>
<p>
To retrieve an
<code class="literal">
AUTO_INCREMENT
</code>
value after
inserting a row, use the
<a class="link" href="information-functions.html#function_last-insert-id">
<code class="literal">
LAST_INSERT_ID()
</code>
</a>
SQL function
or the
<a class="ulink" href="/doc/c-api/8.4/en/mysql-insert-id.html" target="_top">
<code class="literal">
mysql_insert_id()
</code>
</a>
C API
function. See
<a class="xref" href="information-functions.html" title="14.15 Information Functions">
Section 14.15, “Information Functions”
</a>
, and
<a class="ulink" href="/doc/c-api/8.4/en/mysql-insert-id.html" target="_top">
mysql_insert_id()
</a>
.
</p>
<p>
If the
<a class="link" href="sql-mode.html#sqlmode_no_auto_value_on_zero">
<code class="literal">
NO_AUTO_VALUE_ON_ZERO
</code>
</a>
SQL mode is enabled, you can store
<code class="literal">
0
</code>
in
<code class="literal">
AUTO_INCREMENT
</code>
columns as
<code class="literal">
0
</code>
without generating a new sequence value.
See
<a class="xref" href="sql-mode.html" title="7.1.11 Server SQL Modes">
Section 7.1.11, “Server SQL Modes”
</a>
.
</p>
<p>
There can be only one
<code class="literal">
AUTO_INCREMENT
</code>
column
per table, it must be indexed, and it cannot have a
<code class="literal">
DEFAULT
</code>
value. An
<code class="literal">
AUTO_INCREMENT
</code>
column works properly only
if it contains only positive values. Inserting a negative
number is regarded as inserting a very large positive number.
This is done to avoid precision problems when numbers
<span class="quote">
“
<span class="quote">
wrap
</span>
”
</span>
over from positive to negative and also to
ensure that you do not accidentally get an
<code class="literal">
AUTO_INCREMENT
</code>
column that contains
<code class="literal">
0
</code>
.
</p>
<p>
For
<code class="literal">
MyISAM
</code>
tables, you can specify an
<code class="literal">
AUTO_INCREMENT
</code>
secondary column in a
multiple-column key. See
<a class="xref" href="example-auto-increment.html" title="5.6.9 Using AUTO_INCREMENT">
Section 5.6.9, “Using AUTO_INCREMENT”
</a>
.
</p>
<a class="indexterm" name="idm46045186395984">
</a>
<a class="indexterm" name="idm46045186394912">
</a>
<p>
To make MySQL compatible with some ODBC applications, you can
find the
<code class="literal">
AUTO_INCREMENT
</code>
value for the last
inserted row with the following query:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa81083193"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> <em class="replaceable">tbl_name</em> <span class="token keyword">WHERE</span> <em class="replaceable">auto_col</em> <span class="token operator">IS</span> <span class="token boolean">NULL</span></code></pre>
</div>
<p>
This method requires that
<a class="link" href="server-system-variables.html#sysvar_sql_auto_is_null">
<code class="literal">
sql_auto_is_null
</code>
</a>
variable is
not set to 0. See
<a class="xref" href="server-system-variables.html" title="7.1.8 Server System Variables">
Section 7.1.8, “Server System Variables”
</a>
.
</p>
<p>
For information about
<code class="literal">
InnoDB
</code>
and
<code class="literal">
AUTO_INCREMENT
</code>
, see
<a class="xref" href="innodb-auto-increment-handling.html" title="17.6.1.6 AUTO_INCREMENT Handling in InnoDB">
Section 17.6.1.6, “AUTO_INCREMENT Handling in InnoDB”
</a>
. For
information about
<code class="literal">
AUTO_INCREMENT
</code>
and MySQL
Replication, see
<a class="xref" href="replication-features-auto-increment.html" title="19.5.1.1 Replication and AUTO_INCREMENT">
Section 19.5.1.1, “Replication and AUTO_INCREMENT”
</a>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
COMMENT
</code>
</p>
<a class="indexterm" name="idm46045186382384">
</a>
<p>
A comment for a column can be specified with the
<code class="literal">
COMMENT
</code>
option, up to 1024 characters long.
The comment is displayed by the
<a class="link" href="show-create-table.html" title="15.7.7.11 SHOW CREATE TABLE Statement">
<code class="literal">
SHOW
CREATE TABLE
</code>
</a>
and
<a class="link" href="show-columns.html" title="15.7.7.6 SHOW COLUMNS Statement">
<code class="literal">
SHOW FULL
COLUMNS
</code>
</a>
statements. It is also shown in the
<code class="literal">
COLUMN_COMMENT
</code>
column of the Information
Schema
<a class="link" href="information-schema-columns-table.html" title="28.3.8 The INFORMATION_SCHEMA COLUMNS Table">
<code class="literal">
COLUMNS
</code>
</a>
table.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
COLUMN_FORMAT
</code>
</p>
<a class="indexterm" name="idm46045186374064">
</a>
<p>
In NDB Cluster, it is also possible to specify a data storage
format for individual columns of
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDB
</code>
</a>
tables using
<code class="literal">
COLUMN_FORMAT
</code>
. Permissible column formats
are
<code class="literal">
FIXED
</code>
,
<code class="literal">
DYNAMIC
</code>
, and
<code class="literal">
DEFAULT
</code>
.
<code class="literal">
FIXED
</code>
is used
to specify fixed-width storage,
<code class="literal">
DYNAMIC
</code>
permits the column to be variable-width, and
<code class="literal">
DEFAULT
</code>
causes the column to use
fixed-width or variable-width storage as determined by the
column's data type (possibly overridden by a
<code class="literal">
ROW_FORMAT
</code>
specifier).
</p>
<p>
For
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDB
</code>
</a>
tables, the default value
for
<code class="literal">
COLUMN_FORMAT
</code>
is
<code class="literal">
FIXED
</code>
.
</p>
<p>
In NDB Cluster, the maximum possible offset for a column
defined with
<code class="literal">
COLUMN_FORMAT=FIXED
</code>
is 8188
bytes. For more information and possible workarounds, see
<a class="xref" href="mysql-cluster-limitations-database-objects.html" title="25.2.7.5 Limits Associated with Database Objects in NDB Cluster">
Section 25.2.7.5, “Limits Associated with Database Objects in NDB Cluster”
</a>
.
</p>
<p>
<code class="literal">
COLUMN_FORMAT
</code>
currently has no effect on
columns of tables using storage engines other than
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDB
</code>
</a>
. MySQL 8.4
silently ignores
<code class="literal">
COLUMN_FORMAT
</code>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
ENGINE_ATTRIBUTE
</code>
and
<code class="literal">
SECONDARY_ENGINE_ATTRIBUTE
</code>
options are used
to specify column attributes for primary and secondary storage
engines. The options are reserved for future use.
</p>
<p>
The value assigned to this option is a string literal
containing a valid JSON document or an empty string ('').
Invalid JSON is rejected.
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa16901957"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> t1 <span class="token punctuation">(</span>c1 <span class="token datatype">INT</span> <span class="token keyword">ENGINE_ATTRIBUTE</span><span class="token operator">=</span><span class="token string">'{"<em class="replaceable">key</em>":"<em class="replaceable">value</em>"}'</span><span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
<code class="literal">
ENGINE_ATTRIBUTE
</code>
and
<code class="literal">
SECONDARY_ENGINE_ATTRIBUTE
</code>
values can be
repeated without error. In this case, the last specified value
is used.
</p>
<p>
<code class="literal">
ENGINE_ATTRIBUTE
</code>
and
<code class="literal">
SECONDARY_ENGINE_ATTRIBUTE
</code>
values are not
checked by the server, nor are they cleared when the
table's storage engine is changed.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
STORAGE
</code>
</p>
<a class="indexterm" name="idm46045186346864">
</a>
<p>
For
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDB
</code>
</a>
tables, it is possible to
specify whether the column is stored on disk or in memory by
using a
<code class="literal">
STORAGE
</code>
clause.
<code class="literal">
STORAGE
DISK
</code>
causes the column to be stored on disk, and
<code class="literal">
STORAGE MEMORY
</code>
causes in-memory storage to
be used. The
<a class="link" href="create-table.html" title="15.1.20 CREATE TABLE Statement">
<code class="literal">
CREATE TABLE
</code>
</a>
statement used must still include a
<code class="literal">
TABLESPACE
</code>
clause:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa83009651"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> t1 <span class="token punctuation">(</span>
<span class="token prompt"> -></span> c1 <span class="token datatype">INT</span> <span class="token keyword">STORAGE</span> <span class="token keyword">DISK</span><span class="token punctuation">,</span>
<span class="token prompt"> -></span> c2 <span class="token datatype">INT</span> <span class="token keyword">STORAGE</span> <span class="token keyword">MEMORY</span>
<span class="token prompt"> -></span> <span class="token punctuation">)</span> <span class="token keyword">ENGINE</span> <span class="token keyword">NDB</span><span class="token punctuation">;</span>
<span class="token output">ERROR 1005 (HY000)<span class="token punctuation">:</span> Can't create table 'c.t1' (errno<span class="token punctuation">:</span> 140)
</span>
<span class="token prompt">mysql></span> <span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> t1 <span class="token punctuation">(</span>
<span class="token prompt"> -></span> c1 <span class="token datatype">INT</span> <span class="token keyword">STORAGE</span> <span class="token keyword">DISK</span><span class="token punctuation">,</span>
<span class="token prompt"> -></span> c2 <span class="token datatype">INT</span> <span class="token keyword">STORAGE</span> <span class="token keyword">MEMORY</span>
<span class="token prompt"> -></span> <span class="token punctuation">)</span> <span class="token keyword">TABLESPACE</span> ts_1 <span class="token keyword">ENGINE</span> <span class="token keyword">NDB</span><span class="token punctuation">;</span>
<span class="token output">Query OK, 0 rows affected (1.06 sec)</span></code></pre>
</div>
<p>
For
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDB
</code>
</a>
tables,
<code class="literal">
STORAGE
DEFAULT
</code>
is equivalent to
<code class="literal">
STORAGE
MEMORY
</code>
.
</p>
<p>
The
<code class="literal">
STORAGE
</code>
clause has no effect on tables
using storage engines other than
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDB
</code>
</a>
. The
<code class="literal">
STORAGE
</code>
keyword is supported only in the
build of
<a class="link" href="mysqld.html" title="6.3.1 mysqld — The MySQL Server">
<span class="command">
<strong>
mysqld
</strong>
</span>
</a>
that is supplied with NDB
Cluster; it is not recognized in any other version of MySQL,
where any attempt to use the
<code class="literal">
STORAGE
</code>
keyword causes a syntax error.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
GENERATED ALWAYS
</code>
</p>
<p>
Used to specify a generated column expression. For information
about
<a class="link" href="glossary.html#glos_generated_column" title="generated column">
generated
columns
</a>
, see
<a class="xref" href="create-table-generated-columns.html" title="15.1.20.8 CREATE TABLE and Generated Columns">
Section 15.1.20.8, “CREATE TABLE and Generated Columns”
</a>
.
</p>
<p>
<a class="link" href="glossary.html#glos_stored_generated_column" title="stored generated column">
Stored generated
columns
</a>
can be indexed.
<code class="literal">
InnoDB
</code>
supports secondary indexes on
<a class="link" href="glossary.html#glos_virtual_generated_column" title="virtual generated column">
virtual
generated columns
</a>
. See
<a class="xref" href="create-table-secondary-indexes.html" title="15.1.20.9 Secondary Indexes and Generated Columns">
Section 15.1.20.9, “Secondary Indexes and Generated Columns”
</a>
.
</p>
</li>
</ul>
</div>
<h4>
<a name="create-table-indexes-keys">
</a>
Indexes, Foreign Keys, and CHECK Constraints
</h4>
<p>
Several keywords apply to creation of indexes, foreign keys, and
<code class="literal">
CHECK
</code>
constraints. For general background in
addition to the following descriptions, see
<a class="xref" href="create-index.html" title="15.1.15 CREATE INDEX Statement">
Section 15.1.15, “CREATE INDEX Statement”
</a>
,
<a class="xref" href="create-table-foreign-keys.html" title="15.1.20.5 FOREIGN KEY Constraints">
Section 15.1.20.5, “FOREIGN KEY Constraints”
</a>
, and
<a class="xref" href="create-table-check-constraints.html" title="15.1.20.6 CHECK Constraints">
Section 15.1.20.6, “CHECK Constraints”
</a>
.
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<code class="literal">
CONSTRAINT
<em class="replaceable">
<code>
symbol
</code>
</em>
</code>
</p>
<p>
The
<code class="literal">
CONSTRAINT
<em class="replaceable">
<code>
symbol
</code>
</em>
</code>
clause may be
given to name a constraint. If the clause is not given, or a
<em class="replaceable">
<code>
symbol
</code>
</em>
is not included following
the
<code class="literal">
CONSTRAINT
</code>
keyword, MySQL automatically
generates a constraint name, with the exception noted below.
The
<em class="replaceable">
<code>
symbol
</code>
</em>
value, if used, must be
unique per schema (database), per constraint type. A duplicate
<em class="replaceable">
<code>
symbol
</code>
</em>
results in an error. See
also the discussion about length limits of generated
constraint identifiers at
<a class="xref" href="identifier-length.html" title="11.2.1 Identifier Length Limits">
Section 11.2.1, “Identifier Length Limits”
</a>
.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
If the
<code class="literal">
CONSTRAINT
<em class="replaceable">
<code>
symbol
</code>
</em>
</code>
clause is not
given in a foreign key definition, or a
<em class="replaceable">
<code>
symbol
</code>
</em>
is not included following
the
<code class="literal">
CONSTRAINT
</code>
keyword, MySQL
automatically generates a constraint name.
</p>
</div>
<p>
The SQL standard specifies that all types of constraints
(primary key, unique index, foreign key, check) belong to the
same namespace. In MySQL, each constraint type has its own
namespace per schema. Consequently, names for each type of
constraint must be unique per schema, but constraints of
different types can have the same name.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
PRIMARY KEY
</code>
</p>
<a class="indexterm" name="idm46045186300288">
</a>
<p>
A unique index where all key columns must be defined as
<code class="literal">
NOT NULL
</code>
. If they are not explicitly
declared as
<code class="literal">
NOT NULL
</code>
, MySQL declares them
so implicitly (and silently). A table can have only one
<code class="literal">
PRIMARY KEY
</code>
. The name of a
<code class="literal">
PRIMARY
KEY
</code>
is always
<code class="literal">
PRIMARY
</code>
, which thus
cannot be used as the name for any other kind of index.
</p>
<p>
If you do not have a
<code class="literal">
PRIMARY KEY
</code>
and an
application asks for the
<code class="literal">
PRIMARY KEY
</code>
in
your tables, MySQL returns the first
<code class="literal">
UNIQUE
</code>
index that has no
<code class="literal">
NULL
</code>
columns as the
<code class="literal">
PRIMARY KEY
</code>
.
</p>
<p>
In
<code class="literal">
InnoDB
</code>
tables, keep the
<code class="literal">
PRIMARY
KEY
</code>
short to minimize storage overhead for secondary
indexes. Each secondary index entry contains a copy of the
primary key columns for the corresponding row. (See
<a class="xref" href="innodb-index-types.html" title="17.6.2.1 Clustered and Secondary Indexes">
Section 17.6.2.1, “Clustered and Secondary Indexes”
</a>
.)
</p>
<p>
In the created table, a
<code class="literal">
PRIMARY KEY
</code>
is
placed first, followed by all
<code class="literal">
UNIQUE
</code>
indexes, and then the nonunique indexes. This helps the MySQL
optimizer to prioritize which index to use and also more
quickly to detect duplicated
<code class="literal">
UNIQUE
</code>
keys.
</p>
<p>
A
<code class="literal">
PRIMARY KEY
</code>
can be a multiple-column
index. However, you cannot create a multiple-column index
using the
<code class="literal">
PRIMARY KEY
</code>
key attribute in a
column specification. Doing so only marks that single column
as primary. You must use a separate
<code class="literal">
PRIMARY
KEY(
<em class="replaceable">
<code>
key_part
</code>
</em>
, ...)
</code>
clause.
</p>
<a class="indexterm" name="idm46045186282080">
</a>
<p>
If a table has a
<code class="literal">
PRIMARY KEY
</code>
or
<code class="literal">
UNIQUE NOT NULL
</code>
index that consists of a
single column that has an integer type, you can use
<code class="literal">
_rowid
</code>
to refer to the indexed column in
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT
</code>
</a>
statements, as described
in
<a class="xref" href="create-index.html#create-index-unique" title="Unique Indexes">
Unique Indexes
</a>
.
</p>
<p>
In MySQL, the name of a
<code class="literal">
PRIMARY KEY
</code>
is
<code class="literal">
PRIMARY
</code>
. For other indexes, if you do not
assign a name, the index is assigned the same name as the
first indexed column, with an optional suffix
(
<code class="literal">
_2
</code>
,
<code class="literal">
_3
</code>
,
<code class="literal">
...
</code>
) to make it unique. You can see index
names for a table using
<code class="literal">
SHOW INDEX FROM
<em class="replaceable">
<code>
tbl_name
</code>
</em>
</code>
. See
<a class="xref" href="show-index.html" title="15.7.7.23 SHOW INDEX Statement">
Section 15.7.7.23, “SHOW INDEX Statement”
</a>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
KEY | INDEX
</code>
</p>
<p>
<code class="literal">
KEY
</code>
is normally a synonym for
<code class="literal">
INDEX
</code>
. The key attribute
<code class="literal">
PRIMARY
KEY
</code>
can also be specified as just
<code class="literal">
KEY
</code>
when given in a column definition. This
was implemented for compatibility with other database systems.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
UNIQUE
</code>
</p>
<p>
A
<code class="literal">
UNIQUE
</code>
index creates a constraint such
that all values in the index must be distinct. An error occurs
if you try to add a new row with a key value that matches an
existing row. For all engines, a
<code class="literal">
UNIQUE
</code>
index permits multiple
<code class="literal">
NULL
</code>
values for
columns that can contain
<code class="literal">
NULL
</code>
. If you
specify a prefix value for a column in a
<code class="literal">
UNIQUE
</code>
index, the column values must be
unique within the prefix length.
</p>
<a class="indexterm" name="idm46045186259392">
</a>
<p>
If a table has a
<code class="literal">
PRIMARY KEY
</code>
or
<code class="literal">
UNIQUE NOT NULL
</code>
index that consists of a
single column that has an integer type, you can use
<code class="literal">
_rowid
</code>
to refer to the indexed column in
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT
</code>
</a>
statements, as described
in
<a class="xref" href="create-index.html#create-index-unique" title="Unique Indexes">
Unique Indexes
</a>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
FULLTEXT
</code>
</p>
<p>
A
<code class="literal">
FULLTEXT
</code>
index is a special type of index
used for full-text searches. Only the
<a class="link" href="innodb-storage-engine.html" title="Chapter 17 The InnoDB Storage Engine">
<code class="literal">
InnoDB
</code>
</a>
and
<a class="link" href="myisam-storage-engine.html" title="18.2 The MyISAM Storage Engine">
<code class="literal">
MyISAM
</code>
</a>
storage engines support
<code class="literal">
FULLTEXT
</code>
indexes. They can be created only
from
<a class="link" href="char.html" title="13.3.2 The CHAR and VARCHAR Types">
<code class="literal">
CHAR
</code>
</a>
,
<a class="link" href="char.html" title="13.3.2 The CHAR and VARCHAR Types">
<code class="literal">
VARCHAR
</code>
</a>
, and
<a class="link" href="blob.html" title="13.3.4 The BLOB and TEXT Types">
<code class="literal">
TEXT
</code>
</a>
columns. Indexing always
happens over the entire column; column prefix indexing is not
supported and any prefix length is ignored if specified. See
<a class="xref" href="fulltext-search.html" title="14.9 Full-Text Search Functions">
Section 14.9, “Full-Text Search Functions”
</a>
, for details of operation. A
<code class="literal">
WITH PARSER
</code>
clause can be specified as an
<em class="replaceable">
<code>
index_option
</code>
</em>
value to associate a
parser plugin with the index if full-text indexing and
searching operations need special handling. This clause is
valid only for
<code class="literal">
FULLTEXT
</code>
indexes.
<a class="link" href="innodb-storage-engine.html" title="Chapter 17 The InnoDB Storage Engine">
<code class="literal">
InnoDB
</code>
</a>
and
<a class="link" href="myisam-storage-engine.html" title="18.2 The MyISAM Storage Engine">
<code class="literal">
MyISAM
</code>
</a>
support full-text parser
plugins. See
<a class="ulink" href="/doc/extending-mysql/8.4/en/plugin-types.html#full-text-plugin-type" target="_top">
Full-Text Parser Plugins
</a>
and
<a class="ulink" href="/doc/extending-mysql/8.4/en/writing-full-text-plugins.html" target="_top">
Writing Full-Text Parser Plugins
</a>
for more
information.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
SPATIAL
</code>
</p>
<p>
You can create
<code class="literal">
SPATIAL
</code>
indexes on spatial
data types. Spatial types are supported only for
<code class="literal">
InnoDB
</code>
and
<code class="literal">
MyISAM
</code>
tables, and indexed columns must be declared as
<code class="literal">
NOT
NULL
</code>
. See
<a class="xref" href="spatial-types.html" title="13.4 Spatial Data Types">
Section 13.4, “Spatial Data Types”
</a>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
FOREIGN KEY
</code>
</p>
<p>
MySQL supports foreign keys, which let you cross-reference
related data across tables, and foreign key constraints, which
help keep this spread-out data consistent. For definition and
option information, see
<a class="link" href="create-table.html#create-table-reference-definition">
<em class="replaceable">
<code>
reference_definition
</code>
</em>
</a>
,
and
<a class="link" href="create-table.html#create-table-reference-option">
<em class="replaceable">
<code>
reference_option
</code>
</em>
</a>
.
</p>
<p>
Partitioned tables employing the
<a class="link" href="innodb-storage-engine.html" title="Chapter 17 The InnoDB Storage Engine">
<code class="literal">
InnoDB
</code>
</a>
storage engine do not
support foreign keys. See
<a class="xref" href="partitioning-limitations.html" title="26.6 Restrictions and Limitations on Partitioning">
Section 26.6, “Restrictions and Limitations on Partitioning”
</a>
, for more
information.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
CHECK
</code>
</p>
<p>
The
<code class="literal">
CHECK
</code>
clause enables the creation of
constraints to be checked for data values in table rows. See
<a class="xref" href="create-table-check-constraints.html" title="15.1.20.6 CHECK Constraints">
Section 15.1.20.6, “CHECK Constraints”
</a>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
<em class="replaceable">
<code>
key_part
</code>
</em>
</code>
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<p>
A
<em class="replaceable">
<code>
key_part
</code>
</em>
specification can
end with
<code class="literal">
ASC
</code>
or
<code class="literal">
DESC
</code>
to specify whether index values are stored in ascending or
descending order. The default is ascending if no order
specifier is given.
</p>
</li>
<li class="listitem">
<p>
Prefixes, defined by the
<em class="replaceable">
<code>
length
</code>
</em>
attribute, can be up to 767 bytes long for
<code class="literal">
InnoDB
</code>
tables that use the
<code class="literal">
<a class="link" href="glossary.html#glos_redundant_row_format" title="redundant row format">
REDUNDANT
</a>
</code>
or
<code class="literal">
<a class="link" href="glossary.html#glos_compact_row_format" title="compact row format">
COMPACT
</a>
</code>
row format. The prefix length limit is 3072 bytes for
<code class="literal">
InnoDB
</code>
tables that use the
<code class="literal">
<a class="link" href="glossary.html#glos_dynamic_row_format" title="dynamic row format">
DYNAMIC
</a>
</code>
or
<code class="literal">
<a class="link" href="glossary.html#glos_compressed_row_format" title="compressed row format">
COMPRESSED
</a>
</code>
row format. For
<code class="literal">
MyISAM
</code>
tables, the
prefix length limit is 1000 bytes.
</p>
<p>
Prefix
<span class="emphasis">
<em>
limits
</em>
</span>
are measured in bytes.
However, prefix
<span class="emphasis">
<em>
lengths
</em>
</span>
for index
specifications in
<a class="link" href="create-table.html" title="15.1.20 CREATE TABLE Statement">
<code class="literal">
CREATE
TABLE
</code>
</a>
,
<a class="link" href="alter-table.html" title="15.1.9 ALTER TABLE Statement">
<code class="literal">
ALTER
TABLE
</code>
</a>
, and
<a class="link" href="create-index.html" title="15.1.15 CREATE INDEX Statement">
<code class="literal">
CREATE
INDEX
</code>
</a>
statements are interpreted as number of
characters for nonbinary string types
(
<a class="link" href="char.html" title="13.3.2 The CHAR and VARCHAR Types">
<code class="literal">
CHAR
</code>
</a>
,
<a class="link" href="char.html" title="13.3.2 The CHAR and VARCHAR Types">
<code class="literal">
VARCHAR
</code>
</a>
,
<a class="link" href="blob.html" title="13.3.4 The BLOB and TEXT Types">
<code class="literal">
TEXT
</code>
</a>
) and number of bytes
for binary string types
(
<a class="link" href="binary-varbinary.html" title="13.3.3 The BINARY and VARBINARY Types">
<code class="literal">
BINARY
</code>
</a>
,
<a class="link" href="binary-varbinary.html" title="13.3.3 The BINARY and VARBINARY Types">
<code class="literal">
VARBINARY
</code>
</a>
,
<a class="link" href="blob.html" title="13.3.4 The BLOB and TEXT Types">
<code class="literal">
BLOB
</code>
</a>
). Take this into
account when specifying a prefix length for a nonbinary
string column that uses a multibyte character set.
</p>
</li>
<li class="listitem">
<p>
The
<em class="replaceable">
<code>
expr
</code>
</em>
for a
<em class="replaceable">
<code>
key_part
</code>
</em>
specification can take
the form
<code class="literal">
(CAST
<em class="replaceable">
<code>
json_path
</code>
</em>
AS
<em class="replaceable">
<code>
type
</code>
</em>
ARRAY)
</code>
to create
a multi-valued index on a
<a class="link" href="json.html" title="13.5 The JSON Data Type">
<code class="literal">
JSON
</code>
</a>
column.
<a class="xref" href="create-index.html#create-index-multi-valued" title="Multi-Valued Indexes">
Multi-Valued Indexes
</a>
, provides
detailed information regarding creation of, usage of, and
restrictions and limitations on multi-valued indexes.
</p>
</li>
</ul>
</div>
</li>
<li class="listitem">
<p>
<code class="literal">
<em class="replaceable">
<code>
index_type
</code>
</em>
</code>
</p>
<p>
Some storage engines permit you to specify an index type when
creating an index. The syntax for the
<em class="replaceable">
<code>
index_type
</code>
</em>
specifier is
<code class="literal">
USING
<em class="replaceable">
<code>
type_name
</code>
</em>
</code>
.
</p>
<p>
Example:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa38036211"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> lookup
<span class="token punctuation">(</span>id <span class="token datatype">INT</span><span class="token punctuation">,</span> <span class="token keyword">INDEX</span> <span class="token keyword">USING</span> <span class="token keyword">BTREE</span> <span class="token punctuation">(</span>id<span class="token punctuation">)</span>
<span class="token punctuation">)</span> <span class="token keyword">ENGINE</span> <span class="token operator">=</span> <span class="token keyword">MEMORY</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
The preferred position for
<code class="literal">
USING
</code>
is after
the index column list. It can be given before the column list,
but support for use of the option in that position is
deprecated and you should expect it to be removed in a future
MySQL release.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
<em class="replaceable">
<code>
index_option
</code>
</em>
</code>
</p>
<p>
<em class="replaceable">
<code>
index_option
</code>
</em>
values specify
additional options for an index.
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<p>
<code class="literal">
KEY_BLOCK_SIZE
</code>
</p>
<p>
For
<a class="link" href="myisam-storage-engine.html" title="18.2 The MyISAM Storage Engine">
<code class="literal">
MyISAM
</code>
</a>
tables,
<code class="literal">
KEY_BLOCK_SIZE
</code>
optionally specifies the
size in bytes to use for index key blocks. The value is
treated as a hint; a different size could be used if
necessary. A
<code class="literal">
KEY_BLOCK_SIZE
</code>
value
specified for an individual index definition overrides the
table-level
<code class="literal">
KEY_BLOCK_SIZE
</code>
value.
</p>
<p>
For information about the table-level
<code class="literal">
KEY_BLOCK_SIZE
</code>
attribute, see
<a class="xref" href="create-table.html#create-table-options" title="Table Options">
Table Options
</a>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
WITH PARSER
</code>
</p>
<p>
The
<code class="literal">
WITH PARSER
</code>
option can be used only
with
<code class="literal">
FULLTEXT
</code>
indexes. It associates a
parser plugin with the index if full-text indexing and
searching operations need special handling.
<a class="link" href="innodb-storage-engine.html" title="Chapter 17 The InnoDB Storage Engine">
<code class="literal">
InnoDB
</code>
</a>
and
<a class="link" href="myisam-storage-engine.html" title="18.2 The MyISAM Storage Engine">
<code class="literal">
MyISAM
</code>
</a>
support full-text
parser plugins. If you have a
<a class="link" href="myisam-storage-engine.html" title="18.2 The MyISAM Storage Engine">
<code class="literal">
MyISAM
</code>
</a>
table with an
associated full-text parser plugin, you can convert the
table to
<code class="literal">
InnoDB
</code>
using
<code class="literal">
ALTER
TABLE
</code>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
COMMENT
</code>
</p>
<p>
Index definitions can include an optional comment of up to
1024 characters.
</p>
<p>
You can set the
<code class="literal">
InnoDB
</code>
<code class="literal">
MERGE_THRESHOLD
</code>
value for an individual
index using the
<code class="literal">
<em class="replaceable">
<code>
index_option
</code>
</em>
</code>
<code class="literal">
COMMENT
</code>
clause. See
<a class="xref" href="index-page-merge-threshold.html" title="17.8.11 Configuring the Merge Threshold for Index Pages">
Section 17.8.11, “Configuring the Merge Threshold for Index Pages”
</a>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
VISIBLE
</code>
,
<code class="literal">
INVISIBLE
</code>
</p>
<p>
Specify index visibility. Indexes are visible by default.
An invisible index is not used by the optimizer.
Specification of index visibility applies to indexes other
than primary keys (either explicit or implicit). For more
information, see
<a class="xref" href="invisible-indexes.html" title="10.3.12 Invisible Indexes">
Section 10.3.12, “Invisible Indexes”
</a>
.
</p>
<a class="indexterm" name="idm46045186154064">
</a>
</li>
<li class="listitem">
<p>
<code class="literal">
ENGINE_ATTRIBUTE
</code>
and
<code class="literal">
SECONDARY_ENGINE_ATTRIBUTE
</code>
options are
used to specify index attributes for primary and secondary
storage engines. The options are reserved for future use.
</p>
</li>
</ul>
</div>
<p>
For more information about permissible
<em class="replaceable">
<code>
index_option
</code>
</em>
values, see
<a class="xref" href="create-index.html" title="15.1.15 CREATE INDEX Statement">
Section 15.1.15, “CREATE INDEX Statement”
</a>
. For more information about
indexes, see
<a class="xref" href="mysql-indexes.html" title="10.3.1 How MySQL Uses Indexes">
Section 10.3.1, “How MySQL Uses Indexes”
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a name="create-table-reference-definition">
</a>
<code class="literal">
<em class="replaceable">
<code>
reference_definition
</code>
</em>
</code>
</p>
<p>
For
<em class="replaceable">
<code>
reference_definition
</code>
</em>
syntax
details and examples, see
<a class="xref" href="create-table-foreign-keys.html" title="15.1.20.5 FOREIGN KEY Constraints">
Section 15.1.20.5, “FOREIGN KEY Constraints”
</a>
.
</p>
<p>
<a class="link" href="innodb-storage-engine.html" title="Chapter 17 The InnoDB Storage Engine">
<code class="literal">
InnoDB
</code>
</a>
and
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDB
</code>
</a>
tables support checking of
foreign key constraints. The columns of the referenced table
must always be explicitly named. Both
<code class="literal">
ON
DELETE
</code>
and
<code class="literal">
ON UPDATE
</code>
actions on
foreign keys are supported. For more detailed information and
examples, see
<a class="xref" href="create-table-foreign-keys.html" title="15.1.20.5 FOREIGN KEY Constraints">
Section 15.1.20.5, “FOREIGN KEY Constraints”
</a>
.
</p>
<p>
For other storage engines, MySQL Server parses and ignores the
<code class="literal">
FOREIGN KEY
</code>
syntax in
<a class="link" href="create-table.html" title="15.1.20 CREATE TABLE Statement">
<code class="literal">
CREATE TABLE
</code>
</a>
statements.
</p>
<div class="important" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Important
</div>
<p>
For users familiar with the ANSI/ISO SQL Standard, please
note that no storage engine, including
<code class="literal">
InnoDB
</code>
, recognizes or enforces the
<code class="literal">
MATCH
</code>
clause used in referential
integrity constraint definitions. Use of an explicit
<code class="literal">
MATCH
</code>
clause does not have the specified
effect, and also causes
<code class="literal">
ON DELETE
</code>
and
<code class="literal">
ON UPDATE
</code>
clauses to be ignored. For
these reasons, specifying
<code class="literal">
MATCH
</code>
should be
avoided.
</p>
<p>
The
<code class="literal">
MATCH
</code>
clause in the SQL standard
controls how
<code class="literal">
NULL
</code>
values in a composite
(multiple-column) foreign key are handled when comparing to
a primary key.
<code class="literal">
InnoDB
</code>
essentially
implements the semantics defined by
<code class="literal">
MATCH
SIMPLE
</code>
, which permit a foreign key to be all or
partially
<code class="literal">
NULL
</code>
. In that case, the (child
table) row containing such a foreign key is permitted to be
inserted, and does not match any row in the referenced
(parent) table. It is possible to implement other semantics
using triggers.
</p>
<p>
Additionally, MySQL requires that the referenced columns be
indexed for performance. However,
<code class="literal">
InnoDB
</code>
does not enforce any requirement that the referenced columns
be declared
<code class="literal">
UNIQUE
</code>
or
<code class="literal">
NOT
NULL
</code>
. The handling of foreign key references to
nonunique keys or keys that contain
<code class="literal">
NULL
</code>
values is not well defined for operations such as
<code class="literal">
UPDATE
</code>
or
<code class="literal">
DELETE
CASCADE
</code>
. You are advised to use foreign keys that
reference only keys that are both
<code class="literal">
UNIQUE
</code>
(or
<code class="literal">
PRIMARY
</code>
) and
<code class="literal">
NOT
NULL
</code>
.
</p>
<p>
MySQL parses but ignores
<span class="quote">
“
<span class="quote">
inline
<code class="literal">
REFERENCES
</code>
specifications
</span>
”
</span>
(as
defined in the SQL standard) where the references are
defined as part of the column specification. MySQL accepts
<code class="literal">
REFERENCES
</code>
clauses only when specified as
part of a separate
<code class="literal">
FOREIGN KEY
</code>
specification. For more information, see
<a class="xref" href="ansi-diff-foreign-keys.html" title="1.7.2.3 FOREIGN KEY Constraint Differences">
Section 1.7.2.3, “FOREIGN KEY Constraint Differences”
</a>
.
</p>
</div>
</li>
<li class="listitem">
<p>
<a name="create-table-reference-option">
</a>
<code class="literal">
<em class="replaceable">
<code>
reference_option
</code>
</em>
</code>
</p>
<p>
For information about the
<code class="literal">
RESTRICT
</code>
,
<code class="literal">
CASCADE
</code>
,
<code class="literal">
SET NULL
</code>
,
<code class="literal">
NO ACTION
</code>
, and
<code class="literal">
SET
DEFAULT
</code>
options, see
<a class="xref" href="create-table-foreign-keys.html" title="15.1.20.5 FOREIGN KEY Constraints">
Section 15.1.20.5, “FOREIGN KEY Constraints”
</a>
.
</p>
</li>
</ul>
</div>
<h4>
<a name="create-table-options">
</a>
Table Options
</h4>
<p>
Table options are used to optimize the behavior of the table. In
most cases, you do not have to specify any of them. These options
apply to all storage engines unless otherwise indicated. Options
that do not apply to a given storage engine may be accepted and
remembered as part of the table definition. Such options then
apply if you later use
<a class="link" href="alter-table.html" title="15.1.9 ALTER TABLE Statement">
<code class="literal">
ALTER TABLE
</code>
</a>
to convert the table to use a different storage engine.
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<code class="literal">
ENGINE
</code>
</p>
<p>
Specifies the storage engine for the table, using one of the
names shown in the following table. The engine name can be
unquoted or quoted. The quoted name
<code class="literal">
'DEFAULT'
</code>
is recognized but ignored.
</p>
<div class="informaltable">
<table summary="Storage engine names permitted for the ENGINE table option and a description of each engine.">
<colgroup>
<col style="width: 25%"/>
<col style="width: 70%"/>
</colgroup>
<thead>
<tr>
<th>
Storage Engine
</th>
<th>
Description
</th>
</tr>
</thead>
<tbody>
<tr>
<td>
<code class="literal">
InnoDB
</code>
</td>
<td>
Transaction-safe tables with row locking and foreign keys. The default
storage engine for new tables. See
<a class="xref" href="innodb-storage-engine.html" title="Chapter 17 The InnoDB Storage Engine">
Chapter 17,
<i>
The InnoDB Storage Engine
</i>
</a>
, and in
particular
<a class="xref" href="innodb-introduction.html" title="17.1 Introduction to InnoDB">
Section 17.1, “Introduction to InnoDB”
</a>
if you
have MySQL experience but are new to
<code class="literal">
InnoDB
</code>
.
</td>
</tr>
<tr>
<td>
<code class="literal">
MyISAM
</code>
</td>
<td>
The binary portable storage engine that is primarily used for read-only
or read-mostly workloads. See
<a class="xref" href="myisam-storage-engine.html" title="18.2 The MyISAM Storage Engine">
Section 18.2, “The MyISAM Storage Engine”
</a>
.
</td>
</tr>
<tr>
<td>
<code class="literal">
MEMORY
</code>
</td>
<td>
The data for this storage engine is stored only in memory. See
<a class="xref" href="memory-storage-engine.html" title="18.3 The MEMORY Storage Engine">
Section 18.3, “The MEMORY Storage Engine”
</a>
.
</td>
</tr>
<tr>
<td>
<code class="literal">
CSV
</code>
</td>
<td>
Tables that store rows in comma-separated values format. See
<a class="xref" href="csv-storage-engine.html" title="18.4 The CSV Storage Engine">
Section 18.4, “The CSV Storage Engine”
</a>
.
</td>
</tr>
<tr>
<td>
<code class="literal">
ARCHIVE
</code>
</td>
<td>
The archiving storage engine. See
<a class="xref" href="archive-storage-engine.html" title="18.5 The ARCHIVE Storage Engine">
Section 18.5, “The ARCHIVE Storage Engine”
</a>
.
</td>
</tr>
<tr>
<td>
<code class="literal">
EXAMPLE
</code>
</td>
<td>
An example engine. See
<a class="xref" href="example-storage-engine.html" title="18.9 The EXAMPLE Storage Engine">
Section 18.9, “The EXAMPLE Storage Engine”
</a>
.
</td>
</tr>
<tr>
<td>
<code class="literal">
FEDERATED
</code>
</td>
<td>
Storage engine that accesses remote tables. See
<a class="xref" href="federated-storage-engine.html" title="18.8 The FEDERATED Storage Engine">
Section 18.8, “The FEDERATED Storage Engine”
</a>
.
</td>
</tr>
<tr>
<td>
<code class="literal">
HEAP
</code>
</td>
<td>
This is a synonym for
<code class="literal">
MEMORY
</code>
.
</td>
</tr>
<tr>
<td>
<code class="literal">
MERGE
</code>
</td>
<td>
A collection of
<code class="literal">
MyISAM
</code>
tables used as one table. Also
known as
<code class="literal">
MRG_MyISAM
</code>
. See
<a class="xref" href="merge-storage-engine.html" title="18.7 The MERGE Storage Engine">
Section 18.7, “The MERGE Storage Engine”
</a>
.
</td>
</tr>
<tr>
<td>
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDB
</code>
</a>
</td>
<td>
Clustered, fault-tolerant, memory-based tables, supporting transactions
and foreign keys. Also known as
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDBCLUSTER
</code>
</a>
. See
<a class="xref" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
Chapter 25,
<i>
MySQL NDB Cluster 8.4
</i>
</a>
.
</td>
</tr>
</tbody>
</table>
</div>
<div class="informaltable">
<table cellpadding="0" cellspacing="0" style="position: fixed; top: 0px; display: none; left: 431px; width: 709px;">
<thead>
<tr>
<th style="width: 186.312px;">
Storage Engine
</th>
<th style="width: 521.688px;">
Description
</th>
</tr>
</thead>
</table>
</div>
<p>
By default, if a storage engine is specified that is not
available, the statement fails with an error. You can override
this behavior by removing
<a class="link" href="sql-mode.html#sqlmode_no_engine_substitution">
<code class="literal">
NO_ENGINE_SUBSTITUTION
</code>
</a>
from
the server SQL mode (see
<a class="xref" href="sql-mode.html" title="7.1.11 Server SQL Modes">
Section 7.1.11, “Server SQL Modes”
</a>
) so that
MySQL allows substitution of the specified engine with the
default storage engine instead. Normally in such cases, this
is
<code class="literal">
InnoDB
</code>
, which is the default value for
the
<a class="link" href="server-system-variables.html#sysvar_default_storage_engine">
<code class="literal">
default_storage_engine
</code>
</a>
system variable. When
<code class="literal">
NO_ENGINE_SUBSTITUTION
</code>
is disabled, a
warning occurs if the storage engine specification is not
honored.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
AUTOEXTEND_SIZE
</code>
</p>
<p>
Defines the amount by which
<code class="literal">
InnoDB
</code>
extends
the size of the tablespace when it becomes full. The setting
must be a multiple of 4MB. The default setting is 0, which
causes the tablespace to be extended according to the implicit
default behavior. For more information, see
<a class="xref" href="innodb-tablespace-autoextend-size.html" title="17.6.3.9 Tablespace AUTOEXTEND_SIZE Configuration">
Section 17.6.3.9, “Tablespace AUTOEXTEND_SIZE Configuration”
</a>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
AUTO_INCREMENT
</code>
</p>
<p>
The initial
<code class="literal">
AUTO_INCREMENT
</code>
value for the
table. In MySQL 8.4, this works for
<code class="literal">
MyISAM
</code>
,
<code class="literal">
MEMORY
</code>
,
<code class="literal">
InnoDB
</code>
, and
<code class="literal">
ARCHIVE
</code>
tables. To set the first auto-increment value for engines that
do not support the
<code class="literal">
AUTO_INCREMENT
</code>
table
option, insert a
<span class="quote">
“
<span class="quote">
dummy
</span>
”
</span>
row with a value one
less than the desired value after creating the table, and then
delete the dummy row.
</p>
<p>
For engines that support the
<code class="literal">
AUTO_INCREMENT
</code>
table option in
<a class="link" href="create-table.html" title="15.1.20 CREATE TABLE Statement">
<code class="literal">
CREATE TABLE
</code>
</a>
statements, you can also use
<code class="literal">
ALTER TABLE
<em class="replaceable">
<code>
tbl_name
</code>
</em>
AUTO_INCREMENT =
<em class="replaceable">
<code>
N
</code>
</em>
</code>
to reset the
<code class="literal">
AUTO_INCREMENT
</code>
value. The value cannot be
set lower than the maximum value currently in the column.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
AVG_ROW_LENGTH
</code>
</p>
<p>
An approximation of the average row length for your table. You
need to set this only for large tables with variable-size
rows.
</p>
<p>
When you create a
<code class="literal">
MyISAM
</code>
table, MySQL uses
the product of the
<code class="literal">
MAX_ROWS
</code>
and
<code class="literal">
AVG_ROW_LENGTH
</code>
options to decide how big
the resulting table is. If you don't specify either option,
the maximum size for
<code class="literal">
MyISAM
</code>
data and index
files is 256TB by default. (If your operating system does not
support files that large, table sizes are constrained by the
file size limit.) If you want to keep down the pointer sizes
to make the index smaller and faster and you don't really need
big files, you can decrease the default pointer size by
setting the
<a class="link" href="server-system-variables.html#sysvar_myisam_data_pointer_size">
<code class="literal">
myisam_data_pointer_size
</code>
</a>
system variable. (See
<a class="xref" href="server-system-variables.html" title="7.1.8 Server System Variables">
Section 7.1.8, “Server System Variables”
</a>
.) If you want all
your tables to be able to grow above the default limit and are
willing to have your tables slightly slower and larger than
necessary, you can increase the default pointer size by
setting this variable. Setting the value to 7 permits table
sizes up to 65,536TB.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
[DEFAULT] CHARACTER SET
</code>
</p>
<p>
Specifies a default character set for the table.
<code class="literal">
CHARSET
</code>
is a synonym for
<code class="literal">
CHARACTER
SET
</code>
. If the character set name is
<code class="literal">
DEFAULT
</code>
, the database character set is
used.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
CHECKSUM
</code>
</p>
<p>
Set this to 1 if you want MySQL to maintain a live checksum
for all rows (that is, a checksum that MySQL updates
automatically as the table changes). This makes the table a
little slower to update, but also makes it easier to find
corrupted tables. The
<a class="link" href="checksum-table.html" title="15.7.3.3 CHECKSUM TABLE Statement">
<code class="literal">
CHECKSUM
TABLE
</code>
</a>
statement reports the checksum.
(
<code class="literal">
MyISAM
</code>
only.)
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
[DEFAULT] COLLATE
</code>
</p>
<p>
Specifies a default collation for the table.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
COMMENT
</code>
</p>
<p>
A comment for the table, up to 2048 characters long.
</p>
<p>
You can set the
<code class="literal">
InnoDB
</code>
<code class="literal">
MERGE_THRESHOLD
</code>
value for a table using the
<code class="literal">
<em class="replaceable">
<code>
table_option
</code>
</em>
</code>
<code class="literal">
COMMENT
</code>
clause. See
<a class="xref" href="index-page-merge-threshold.html" title="17.8.11 Configuring the Merge Threshold for Index Pages">
Section 17.8.11, “Configuring the Merge Threshold for Index Pages”
</a>
.
</p>
<p>
<a name="create-table-comment-ndb-table-options">
</a>
<b>
Setting NDB_TABLE options.
</b>
<a class="indexterm" name="idm46045186012144">
</a>
The table comment in a
<code class="literal">
CREATE TABLE
</code>
that
creates an
<code class="literal">
NDB
</code>
table or an
<a class="link" href="alter-table.html" title="15.1.9 ALTER TABLE Statement">
<code class="literal">
ALTER TABLE
</code>
</a>
statement which
alters one can also be used to specify one to four of the
<code class="literal">
NDB_TABLE
</code>
options
<code class="literal">
NOLOGGING
</code>
,
<code class="literal">
READ_BACKUP
</code>
,
<code class="literal">
PARTITION_BALANCE
</code>
, or
<code class="literal">
FULLY_REPLICATED
</code>
as a set of name-value
pairs, separated by commas if need be, immediately following
the string
<code class="literal">
NDB_TABLE=
</code>
that begins the
quoted comment text. An example statement using this syntax
is shown here (emphasized text):
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa76274175"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> t1 <span class="token punctuation">(</span>
c1 <span class="token datatype">INT</span> <span class="token operator">NOT</span> <span class="token boolean">NULL</span> <span class="token keyword">AUTO_INCREMENT</span> <span class="token keyword">PRIMARY</span> <span class="token keyword">KEY</span><span class="token punctuation">,</span>
c2 <span class="token datatype">VARCHAR</span><span class="token punctuation">(</span><span class="token number">100</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
c3 <span class="token datatype">VARCHAR</span><span class="token punctuation">(</span><span class="token number">100</span><span class="token punctuation">)</span> <span class="token punctuation">)</span>
<span class="token keyword">ENGINE</span><span class="token operator">=</span><span class="token keyword">NDB</span>
<span class="token keyword"></span><em><span class="token keyword">COMMENT</span><span class="token operator">=</span><span class="token string">"NDB_TABLE=READ_BACKUP=0,PARTITION_BALANCE=FOR_RP_BY_NODE"</span></em><span class="token string"></span><span class="token punctuation">;</span></code></pre>
</div>
<p>
Spaces are not permitted within the quoted string. The string
is case-insensitive.
</p>
<p>
The comment is displayed as part of the output of
<a class="link" href="show-create-table.html" title="15.7.7.11 SHOW CREATE TABLE Statement">
<code class="literal">
SHOW CREATE TABLE
</code>
</a>
. The text of
the comment is also available as the TABLE_COMMENT column of
the MySQL Information Schema
<a class="link" href="information-schema-tables-table.html" title="28.3.38 The INFORMATION_SCHEMA TABLES Table">
<code class="literal">
TABLES
</code>
</a>
table.
</p>
<p>
This comment syntax is also supported with
<a class="link" href="alter-table.html" title="15.1.9 ALTER TABLE Statement">
<code class="literal">
ALTER TABLE
</code>
</a>
statements for
<code class="literal">
NDB
</code>
tables. Keep in mind that a table
comment used with
<code class="literal">
ALTER TABLE
</code>
replaces any
existing comment which the table might have had previously.
</p>
<p>
Setting the
<code class="literal">
MERGE_THRESHOLD
</code>
option in table
comments is not supported for
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDB
</code>
</a>
tables (it is ignored).
</p>
<p>
For complete syntax information and examples, see
<a class="xref" href="create-table-ndb-comment-options.html" title="15.1.20.12 Setting NDB Comment Options">
Section 15.1.20.12, “Setting NDB Comment Options”
</a>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
COMPRESSION
</code>
</p>
<p>
The compression algorithm used for page level compression for
<code class="literal">
InnoDB
</code>
tables. Supported values include
<code class="literal">
Zlib
</code>
,
<code class="literal">
LZ4
</code>
, and
<code class="literal">
None
</code>
. The
<code class="literal">
COMPRESSION
</code>
attribute was introduced with the transparent page compression
feature. Page compression is only supported with
<code class="literal">
InnoDB
</code>
tables that reside in
<a class="link" href="glossary.html#glos_file_per_table" title="file-per-table">
file-per-table
</a>
tablespaces, and is only available on Linux and Windows
platforms that support sparse files and hole punching. For
more information, see
<a class="xref" href="innodb-page-compression.html" title="17.9.2 InnoDB Page Compression">
Section 17.9.2, “InnoDB Page Compression”
</a>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
CONNECTION
</code>
</p>
<p>
The connection string for a
<code class="literal">
FEDERATED
</code>
table.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
Older versions of MySQL used a
<code class="literal">
COMMENT
</code>
option for the connection string.
</p>
</div>
</li>
<li class="listitem">
<p>
<code class="literal">
DATA DIRECTORY
</code>
,
<code class="literal">
INDEX
DIRECTORY
</code>
</p>
<p>
For
<code class="literal">
InnoDB
</code>
, the
<code class="literal">
DATA
DIRECTORY='
<em class="replaceable">
<code>
directory
</code>
</em>
'
</code>
clause permits creating tables outside of the data directory.
The
<a class="link" href="innodb-parameters.html#sysvar_innodb_file_per_table">
<code class="literal">
innodb_file_per_table
</code>
</a>
variable must be enabled to use the
<code class="literal">
DATA
DIRECTORY
</code>
clause. The full directory path must be
specified, and known to
<code class="literal">
InnoDB
</code>
. For more
information, see
<a class="xref" href="innodb-create-table-external.html" title="17.6.1.2 Creating Tables Externally">
Section 17.6.1.2, “Creating Tables Externally”
</a>
.
</p>
<p>
When creating
<code class="literal">
MyISAM
</code>
tables, you can use
the
<code class="literal">
DATA
DIRECTORY='
<em class="replaceable">
<code>
directory
</code>
</em>
'
</code>
clause, the
<code class="literal">
INDEX
DIRECTORY='
<em class="replaceable">
<code>
directory
</code>
</em>
'
</code>
clause, or both. They specify where to put a
<code class="literal">
MyISAM
</code>
table's data file and index file,
respectively. Unlike
<code class="literal">
InnoDB
</code>
tables, MySQL
does not create subdirectories that correspond to the database
name when creating a
<code class="literal">
MyISAM
</code>
table with a
<code class="literal">
DATA DIRECTORY
</code>
or
<code class="literal">
INDEX
DIRECTORY
</code>
option. Files are created in the directory
that is specified.
</p>
<p>
You must have the
<a class="link" href="privileges-provided.html#priv_file">
<code class="literal">
FILE
</code>
</a>
privilege to use the
<code class="literal">
DATA DIRECTORY
</code>
or
<code class="literal">
INDEX DIRECTORY
</code>
table option.
</p>
<div class="important" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Important
</div>
<p>
Table-level
<code class="literal">
DATA DIRECTORY
</code>
and
<code class="literal">
INDEX DIRECTORY
</code>
options are ignored for
partitioned tables. (Bug #32091)
</p>
</div>
<p>
These options work only when you are not using the
<a class="link" href="server-options.html#option_mysqld_symbolic-links">
<code class="option">
--skip-symbolic-links
</code>
</a>
option. Your operating system must also have a working,
thread-safe
<code class="literal">
realpath()
</code>
call. See
<a class="xref" href="symbolic-links-to-tables.html" title="10.12.2.2 Using Symbolic Links for MyISAM Tables on Unix">
Section 10.12.2.2, “Using Symbolic Links for MyISAM Tables on Unix”
</a>
, for more complete
information.
</p>
<p>
If a
<code class="literal">
MyISAM
</code>
table is created with no
<code class="literal">
DATA DIRECTORY
</code>
option, the
<code class="filename">
.MYD
</code>
file is created in the database
directory. By default, if
<code class="literal">
MyISAM
</code>
finds an
existing
<code class="filename">
.MYD
</code>
file in this case, it
overwrites it. The same applies to
<code class="filename">
.MYI
</code>
files for tables created with no
<code class="literal">
INDEX
DIRECTORY
</code>
option. To suppress this behavior, start
the server with the
<a class="link" href="server-system-variables.html#sysvar_keep_files_on_create">
<code class="option">
--keep_files_on_create
</code>
</a>
option,
in which case
<code class="literal">
MyISAM
</code>
does not overwrite
existing files and returns an error instead.
</p>
<p>
If a
<code class="literal">
MyISAM
</code>
table is created with a
<code class="literal">
DATA DIRECTORY
</code>
or
<code class="literal">
INDEX
DIRECTORY
</code>
option and an existing
<code class="filename">
.MYD
</code>
or
<code class="filename">
.MYI
</code>
file is
found,
<code class="literal">
MyISAM
</code>
always returns an error, and
does not overwrite a file in the specified directory.
</p>
<div class="important" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Important
</div>
<p>
You cannot use path names that contain the MySQL data
directory with
<code class="literal">
DATA DIRECTORY
</code>
or
<code class="literal">
INDEX DIRECTORY
</code>
. This includes
partitioned tables and individual table partitions. (See Bug
#32167.)
</p>
</div>
</li>
<li class="listitem">
<p>
<code class="literal">
DELAY_KEY_WRITE
</code>
</p>
<p>
Set this to 1 if you want to delay key updates for the table
until the table is closed. See the description of the
<a class="link" href="server-system-variables.html#sysvar_delay_key_write">
<code class="literal">
delay_key_write
</code>
</a>
system
variable in
<a class="xref" href="server-system-variables.html" title="7.1.8 Server System Variables">
Section 7.1.8, “Server System Variables”
</a>
.
(
<code class="literal">
MyISAM
</code>
only.)
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
ENCRYPTION
</code>
</p>
<p>
The
<code class="literal">
ENCRYPTION
</code>
clause enables or disables
page-level data encryption for an
<code class="literal">
InnoDB
</code>
table. A keyring plugin must be installed and configured
before encryption can be enabled. The
<code class="literal">
ENCRYPTION
</code>
clause can be specified when
creating a table in an a file-per-table tablespace, or when
creating a table in a general tablespace.
</p>
<p>
The
<code class="literal">
ENCRYPTION
</code>
option is supported only by
the
<code class="literal">
InnoDB
</code>
storage engine; thus it works
only if the default storage engine is
<code class="literal">
InnoDB
</code>
, or if the
<code class="literal">
CREATE
TABLE
</code>
statement also specifies
<code class="literal">
ENGINE=InnoDB
</code>
. Otherwise the statement is
rejected with
<a class="ulink" href="/doc/mysql-errors/8.4/en/server-error-reference.html#error_er_check_not_implemented" target="_top">
<code class="literal">
ER_CHECK_NOT_IMPLEMENTED
</code>
</a>
.
</p>
<p>
A table inherits the default schema encryption if an
<code class="literal">
ENCRYPTION
</code>
clause is not specified. If the
<a class="link" href="server-system-variables.html#sysvar_table_encryption_privilege_check">
<code class="literal">
table_encryption_privilege_check
</code>
</a>
variable is enabled, the
<a class="link" href="privileges-provided.html#priv_table-encryption-admin">
<code class="literal">
TABLE_ENCRYPTION_ADMIN
</code>
</a>
privilege is required to create a table with an
<code class="literal">
ENCRYPTION
</code>
clause setting that differs from
the default schema encryption. When creating a table in a
general tablespace, table and tablespace encryption must
match.
</p>
<p>
Specifying an
<code class="literal">
ENCRYPTION
</code>
clause with a
value other than
<code class="literal">
'N'
</code>
or
<code class="literal">
''
</code>
is not permitted when using a storage
engine that does not support encryption.
</p>
<p>
For more information, see
<a class="xref" href="innodb-data-encryption.html" title="17.13 InnoDB Data-at-Rest Encryption">
Section 17.13, “InnoDB Data-at-Rest Encryption”
</a>
.
</p>
</li>
<li class="listitem">
<p>
The
<code class="literal">
ENGINE_ATTRIBUTE
</code>
and
<code class="literal">
SECONDARY_ENGINE_ATTRIBUTE
</code>
options are used
to specify table attributes for primary and secondary storage
engines. The options are reserved for future use.
</p>
<p>
The value assigned to either of these options must be a string
literal containing a valid JSON document or an empty string
(''). Invalid JSON is rejected.
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa60629812"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> t1 <span class="token punctuation">(</span>c1 <span class="token datatype">INT</span><span class="token punctuation">)</span> <span class="token keyword">ENGINE_ATTRIBUTE</span><span class="token operator">=</span><span class="token string">'{"<em class="replaceable">key</em>":"<em class="replaceable">value</em>"}'</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
<code class="literal">
ENGINE_ATTRIBUTE
</code>
and
<code class="literal">
SECONDARY_ENGINE_ATTRIBUTE
</code>
values can be
repeated without error. In this case, the last specified value
is used.
</p>
<p>
<code class="literal">
ENGINE_ATTRIBUTE
</code>
and
<code class="literal">
SECONDARY_ENGINE_ATTRIBUTE
</code>
values are not
checked by the server, nor are they cleared when the
table's storage engine is changed.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
INSERT_METHOD
</code>
</p>
<p>
If you want to insert data into a
<code class="literal">
MERGE
</code>
table, you must specify with
<code class="literal">
INSERT_METHOD
</code>
the table into which the row should be inserted.
<code class="literal">
INSERT_METHOD
</code>
is an option useful for
<code class="literal">
MERGE
</code>
tables only. Use a value of
<code class="literal">
FIRST
</code>
or
<code class="literal">
LAST
</code>
to have
inserts go to the first or last table, or a value of
<code class="literal">
NO
</code>
to prevent inserts. See
<a class="xref" href="merge-storage-engine.html" title="18.7 The MERGE Storage Engine">
Section 18.7, “The MERGE Storage Engine”
</a>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
KEY_BLOCK_SIZE
</code>
</p>
<p>
For
<a class="link" href="myisam-storage-engine.html" title="18.2 The MyISAM Storage Engine">
<code class="literal">
MyISAM
</code>
</a>
tables,
<code class="literal">
KEY_BLOCK_SIZE
</code>
optionally specifies the
size in bytes to use for index key blocks. The value is
treated as a hint; a different size could be used if
necessary. A
<code class="literal">
KEY_BLOCK_SIZE
</code>
value specified
for an individual index definition overrides the table-level
<code class="literal">
KEY_BLOCK_SIZE
</code>
value.
</p>
<p>
For
<a class="link" href="innodb-storage-engine.html" title="Chapter 17 The InnoDB Storage Engine">
<code class="literal">
InnoDB
</code>
</a>
tables,
<code class="literal">
KEY_BLOCK_SIZE
</code>
specifies the
<a class="link" href="glossary.html#glos_page" title="page">
page
</a>
size in kilobytes to use
for
<a class="link" href="glossary.html#glos_compression" title="compression">
compressed
</a>
<code class="literal">
InnoDB
</code>
tables. The
<code class="literal">
KEY_BLOCK_SIZE
</code>
value is treated as a hint;
a different size could be used by
<code class="literal">
InnoDB
</code>
if
necessary.
<code class="literal">
KEY_BLOCK_SIZE
</code>
can only be less
than or equal to the
<a class="link" href="innodb-parameters.html#sysvar_innodb_page_size">
<code class="literal">
innodb_page_size
</code>
</a>
value. A
value of 0 represents the default compressed page size, which
is half of the
<a class="link" href="innodb-parameters.html#sysvar_innodb_page_size">
<code class="literal">
innodb_page_size
</code>
</a>
value.
Depending on
<a class="link" href="innodb-parameters.html#sysvar_innodb_page_size">
<code class="literal">
innodb_page_size
</code>
</a>
, possible
<code class="literal">
KEY_BLOCK_SIZE
</code>
values include 0, 1, 2, 4,
8, and 16. See
<a class="xref" href="innodb-table-compression.html" title="17.9.1 InnoDB Table Compression">
Section 17.9.1, “InnoDB Table Compression”
</a>
for
more information.
</p>
<p>
Oracle recommends enabling
<a class="link" href="innodb-parameters.html#sysvar_innodb_strict_mode">
<code class="literal">
innodb_strict_mode
</code>
</a>
when
specifying
<code class="literal">
KEY_BLOCK_SIZE
</code>
for
<code class="literal">
InnoDB
</code>
tables. When
<a class="link" href="innodb-parameters.html#sysvar_innodb_strict_mode">
<code class="literal">
innodb_strict_mode
</code>
</a>
is
enabled, specifying an invalid
<code class="literal">
KEY_BLOCK_SIZE
</code>
value returns an error. If
<a class="link" href="innodb-parameters.html#sysvar_innodb_strict_mode">
<code class="literal">
innodb_strict_mode
</code>
</a>
is
disabled, an invalid
<code class="literal">
KEY_BLOCK_SIZE
</code>
value
results in a warning, and the
<code class="literal">
KEY_BLOCK_SIZE
</code>
option is ignored.
</p>
<p>
The
<code class="literal">
Create_options
</code>
column in response to
<a class="link" href="show-table-status.html" title="15.7.7.38 SHOW TABLE STATUS Statement">
<code class="literal">
SHOW TABLE STATUS
</code>
</a>
reports the
actual
<code class="literal">
KEY_BLOCK_SIZE
</code>
used by the table, as
does
<a class="link" href="show-create-table.html" title="15.7.7.11 SHOW CREATE TABLE Statement">
<code class="literal">
SHOW CREATE TABLE
</code>
</a>
.
</p>
<p>
<code class="literal">
InnoDB
</code>
only supports
<code class="literal">
KEY_BLOCK_SIZE
</code>
at the table level.
</p>
<p>
<code class="literal">
KEY_BLOCK_SIZE
</code>
is not supported with 32KB
and 64KB
<a class="link" href="innodb-parameters.html#sysvar_innodb_page_size">
<code class="literal">
innodb_page_size
</code>
</a>
values.
<code class="literal">
InnoDB
</code>
table compression does not
support these pages sizes.
</p>
<p>
<code class="literal">
InnoDB
</code>
does not support the
<code class="literal">
KEY_BLOCK_SIZE
</code>
option when creating
temporary tables.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
MAX_ROWS
</code>
</p>
<p>
The maximum number of rows you plan to store in the table.
This is not a hard limit, but rather a hint to the storage
engine that the table must be able to store at least this many
rows.
</p>
<a class="indexterm" name="idm46045185861600">
</a>
<a class="indexterm" name="idm46045185860112">
</a>
<a class="indexterm" name="idm46045185858624">
</a>
<a class="indexterm" name="idm46045185857136">
</a>
<div class="important" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Important
</div>
<p>
The use of
<code class="literal">
MAX_ROWS
</code>
with
<code class="literal">
NDB
</code>
tables to control the number of table
partitions is deprecated. It remains supported in later
versions for backward compatibility, but is subject to
removal in a future release. Use PARTITION_BALANCE instead;
see
<a class="xref" href="create-table.html#create-table-comment-ndb-table-options" title="Setting NDB_TABLE options">
Setting NDB_TABLE options
</a>
.
</p>
</div>
<p>
The
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDB
</code>
</a>
storage engine treats
this value as a maximum. If you plan to create very large NDB
Cluster tables (containing millions of rows), you should use
this option to insure that
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDB
</code>
</a>
allocates sufficient number of index slots in the hash table
used for storing hashes of the table's primary keys by
setting
<code class="literal">
MAX_ROWS = 2 *
<em class="replaceable">
<code>
rows
</code>
</em>
</code>
, where
<em class="replaceable">
<code>
rows
</code>
</em>
is the number of rows that you
expect to insert into the table.
</p>
<p>
The maximum
<code class="literal">
MAX_ROWS
</code>
value is 4294967295;
larger values are truncated to this limit.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
MIN_ROWS
</code>
</p>
<p>
The minimum number of rows you plan to store in the table. The
<a class="link" href="memory-storage-engine.html" title="18.3 The MEMORY Storage Engine">
<code class="literal">
MEMORY
</code>
</a>
storage engine uses this
option as a hint about memory use.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
PACK_KEYS
</code>
</p>
<p>
Takes effect only with
<code class="literal">
MyISAM
</code>
tables. Set
this option to 1 if you want to have smaller indexes. This
usually makes updates slower and reads faster. Setting the
option to 0 disables all packing of keys. Setting it to
<code class="literal">
DEFAULT
</code>
tells the storage engine to pack
only long
<a class="link" href="char.html" title="13.3.2 The CHAR and VARCHAR Types">
<code class="literal">
CHAR
</code>
</a>
,
<a class="link" href="char.html" title="13.3.2 The CHAR and VARCHAR Types">
<code class="literal">
VARCHAR
</code>
</a>
,
<a class="link" href="binary-varbinary.html" title="13.3.3 The BINARY and VARBINARY Types">
<code class="literal">
BINARY
</code>
</a>
, or
<a class="link" href="binary-varbinary.html" title="13.3.3 The BINARY and VARBINARY Types">
<code class="literal">
VARBINARY
</code>
</a>
columns.
</p>
<p>
If you do not use
<code class="literal">
PACK_KEYS
</code>
, the default is
to pack strings, but not numbers. If you use
<code class="literal">
PACK_KEYS=1
</code>
, numbers are packed as well.
</p>
<p>
When packing binary number keys, MySQL uses prefix
compression:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<p>
Every key needs one extra byte to indicate how many bytes
of the previous key are the same for the next key.
</p>
</li>
<li class="listitem">
<p>
The pointer to the row is stored in high-byte-first order
directly after the key, to improve compression.
</p>
</li>
</ul>
</div>
<p>
This means that if you have many equal keys on two consecutive
rows, all following
<span class="quote">
“
<span class="quote">
same
</span>
”
</span>
keys usually only take
two bytes (including the pointer to the row). Compare this to
the ordinary case where the following keys takes
<code class="literal">
storage_size_for_key + pointer_size
</code>
(where
the pointer size is usually 4). Conversely, you get a
significant benefit from prefix compression only if you have
many numbers that are the same. If all keys are totally
different, you use one byte more per key, if the key is not a
key that can have
<code class="literal">
NULL
</code>
values. (In this
case, the packed key length is stored in the same byte that is
used to mark if a key is
<code class="literal">
NULL
</code>
.)
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
PASSWORD
</code>
</p>
<p>
This option is unused.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
ROW_FORMAT
</code>
</p>
<p>
Defines the physical format in which the rows are stored.
</p>
<p>
When creating a table with
<a class="link" href="glossary.html#glos_strict_mode" title="strict mode">
strict mode
</a>
disabled,
the storage engine's default row format is used if the
specified row format is not supported. The actual row format
of the table is reported in the
<code class="literal">
Row_format
</code>
column in response to
<a class="link" href="show-table-status.html" title="15.7.7.38 SHOW TABLE STATUS Statement">
<code class="literal">
SHOW TABLE
STATUS
</code>
</a>
. The
<code class="literal">
Create_options
</code>
column
shows the row format that was specified in the
<a class="link" href="create-table.html" title="15.1.20 CREATE TABLE Statement">
<code class="literal">
CREATE TABLE
</code>
</a>
statement, as does
<a class="link" href="show-create-table.html" title="15.7.7.11 SHOW CREATE TABLE Statement">
<code class="literal">
SHOW CREATE TABLE
</code>
</a>
.
</p>
<p>
Row format choices differ depending on the storage engine used
for the table.
</p>
<p>
For
<code class="literal">
InnoDB
</code>
tables:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<p>
The default row format is defined by
<a class="link" href="innodb-parameters.html#sysvar_innodb_default_row_format">
<code class="literal">
innodb_default_row_format
</code>
</a>
,
which has a default setting of
<code class="literal">
DYNAMIC
</code>
.
The default row format is used when the
<code class="literal">
ROW_FORMAT
</code>
option is not defined or
when
<code class="literal">
ROW_FORMAT=DEFAULT
</code>
is used.
</p>
<p>
If the
<code class="literal">
ROW_FORMAT
</code>
option is not
defined, or if
<code class="literal">
ROW_FORMAT=DEFAULT
</code>
is
used, operations that rebuild a table also silently change
the row format of the table to the default defined by
<a class="link" href="innodb-parameters.html#sysvar_innodb_default_row_format">
<code class="literal">
innodb_default_row_format
</code>
</a>
.
For more information, see
<a class="xref" href="innodb-row-format.html#innodb-row-format-defining" title="Defining the Row Format of a Table">
Defining the Row Format of a Table
</a>
.
</p>
</li>
<li class="listitem">
<p>
For more efficient
<code class="literal">
InnoDB
</code>
storage of
data types, especially
<a class="link" href="blob.html" title="13.3.4 The BLOB and TEXT Types">
<code class="literal">
BLOB
</code>
</a>
types, use the
<code class="literal">
DYNAMIC
</code>
. See
<a class="xref" href="innodb-row-format.html#innodb-row-format-dynamic" title="DYNAMIC Row Format">
DYNAMIC Row Format
</a>
for
requirements associated with the
<code class="literal">
DYNAMIC
</code>
row format.
</p>
</li>
<li class="listitem">
<p>
To enable compression for
<code class="literal">
InnoDB
</code>
tables, specify
<code class="literal">
ROW_FORMAT=COMPRESSED
</code>
.
The
<code class="literal">
ROW_FORMAT=COMPRESSED
</code>
option is not
supported when creating temporary tables. See
<a class="xref" href="innodb-compression.html" title="17.9 InnoDB Table and Page Compression">
Section 17.9, “InnoDB Table and Page Compression”
</a>
for requirements
associated with the
<code class="literal">
COMPRESSED
</code>
row
format.
</p>
</li>
<li class="listitem">
<p>
The row format used in older versions of MySQL can still
be requested by specifying the
<code class="literal">
REDUNDANT
</code>
row format.
</p>
</li>
<li class="listitem">
<p>
When you specify a non-default
<code class="literal">
ROW_FORMAT
</code>
clause, consider also
enabling the
<a class="link" href="innodb-parameters.html#sysvar_innodb_strict_mode">
<code class="literal">
innodb_strict_mode
</code>
</a>
configuration option.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
ROW_FORMAT=FIXED
</code>
is not supported. If
<code class="literal">
ROW_FORMAT=FIXED
</code>
is specified while
<a class="link" href="innodb-parameters.html#sysvar_innodb_strict_mode">
<code class="literal">
innodb_strict_mode
</code>
</a>
is
disabled,
<code class="literal">
InnoDB
</code>
issues a warning and
assumes
<code class="literal">
ROW_FORMAT=DYNAMIC
</code>
. If
<code class="literal">
ROW_FORMAT=FIXED
</code>
is specified while
<a class="link" href="innodb-parameters.html#sysvar_innodb_strict_mode">
<code class="literal">
innodb_strict_mode
</code>
</a>
is
enabled, which is the default,
<code class="literal">
InnoDB
</code>
returns an error.
</p>
</li>
<li class="listitem">
<p>
For additional information about
<code class="literal">
InnoDB
</code>
row formats, see
<a class="xref" href="innodb-row-format.html" title="17.10 InnoDB Row Formats">
Section 17.10, “InnoDB Row Formats”
</a>
.
</p>
</li>
</ul>
</div>
<p>
For
<code class="literal">
MyISAM
</code>
tables, the option value can be
<code class="literal">
FIXED
</code>
or
<code class="literal">
DYNAMIC
</code>
for
static or variable-length row format.
<a class="link" href="myisampack.html" title="6.6.6 myisampack — Generate Compressed, Read-Only MyISAM Tables">
<span class="command">
<strong>
myisampack
</strong>
</span>
</a>
sets the type to
<code class="literal">
COMPRESSED
</code>
. See
<a class="xref" href="myisam-table-formats.html" title="18.2.3 MyISAM Table Storage Formats">
Section 18.2.3, “MyISAM Table Storage Formats”
</a>
.
</p>
<p>
For
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDB
</code>
</a>
tables, the default
<code class="literal">
ROW_FORMAT
</code>
is
<code class="literal">
DYNAMIC
</code>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
START TRANSACTION
</code>
</p>
<p>
This is an internal-use table option, used to permit
<code class="literal">
CREATE TABLE ... SELECT
</code>
to be logged as a
single, atomic transaction in the binary log when using
row-based replication with a storage engine that supports
atomic DDL. Only
<a class="link" href="binlog.html" title="15.7.8.1 BINLOG Statement">
<code class="literal">
BINLOG
</code>
</a>
,
<a class="link" href="commit.html" title="15.3.1 START TRANSACTION, COMMIT, and ROLLBACK Statements">
<code class="literal">
COMMIT
</code>
</a>
, and
<a class="link" href="commit.html" title="15.3.1 START TRANSACTION, COMMIT, and ROLLBACK Statements">
<code class="literal">
ROLLBACK
</code>
</a>
statements are permitted after
<code class="literal">
CREATE TABLE ... START
TRANSACTION
</code>
. For related information, see
<a class="xref" href="atomic-ddl.html" title="15.1.1 Atomic Data Definition Statement Support">
Section 15.1.1, “Atomic Data Definition Statement Support”
</a>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
STATS_AUTO_RECALC
</code>
</p>
<p>
Specifies whether to automatically recalculate
<a class="link" href="glossary.html#glos_persistent_statistics" title="persistent statistics">
persistent
statistics
</a>
for an
<code class="literal">
InnoDB
</code>
table. The
value
<code class="literal">
DEFAULT
</code>
causes the persistent
statistics setting for the table to be determined by the
<a class="link" href="innodb-parameters.html#sysvar_innodb_stats_auto_recalc">
<code class="literal">
innodb_stats_auto_recalc
</code>
</a>
configuration option. The value
<code class="literal">
1
</code>
causes
statistics to be recalculated when 10% of the data in the
table has changed. The value
<code class="literal">
0
</code>
prevents
automatic recalculation for this table; with this setting,
issue an
<a class="link" href="analyze-table.html" title="15.7.3.1 ANALYZE TABLE Statement">
<code class="literal">
ANALYZE TABLE
</code>
</a>
statement to recalculate the statistics after making
substantial changes to the table. For more information about
the persistent statistics feature, see
<a class="xref" href="innodb-persistent-stats.html" title="17.8.10.1 Configuring Persistent Optimizer Statistics Parameters">
Section 17.8.10.1, “Configuring Persistent Optimizer Statistics Parameters”
</a>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
STATS_PERSISTENT
</code>
</p>
<p>
Specifies whether to enable
<a class="link" href="glossary.html#glos_persistent_statistics" title="persistent statistics">
persistent
statistics
</a>
for an
<code class="literal">
InnoDB
</code>
table. The
value
<code class="literal">
DEFAULT
</code>
causes the persistent
statistics setting for the table to be determined by the
<a class="link" href="innodb-parameters.html#sysvar_innodb_stats_persistent">
<code class="literal">
innodb_stats_persistent
</code>
</a>
configuration option. The value
<code class="literal">
1
</code>
enables
persistent statistics for the table, while the value
<code class="literal">
0
</code>
turns off this feature. After enabling
persistent statistics through a
<code class="literal">
CREATE
TABLE
</code>
or
<code class="literal">
ALTER TABLE
</code>
statement,
issue an
<a class="link" href="analyze-table.html" title="15.7.3.1 ANALYZE TABLE Statement">
<code class="literal">
ANALYZE TABLE
</code>
</a>
statement to calculate the statistics, after loading
representative data into the table. For more information about
the persistent statistics feature, see
<a class="xref" href="innodb-persistent-stats.html" title="17.8.10.1 Configuring Persistent Optimizer Statistics Parameters">
Section 17.8.10.1, “Configuring Persistent Optimizer Statistics Parameters”
</a>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
STATS_SAMPLE_PAGES
</code>
</p>
<p>
The number of index pages to sample when estimating
cardinality and other statistics for an indexed column, such
as those calculated by
<a class="link" href="analyze-table.html" title="15.7.3.1 ANALYZE TABLE Statement">
<code class="literal">
ANALYZE
TABLE
</code>
</a>
. For more information, see
<a class="xref" href="innodb-persistent-stats.html" title="17.8.10.1 Configuring Persistent Optimizer Statistics Parameters">
Section 17.8.10.1, “Configuring Persistent Optimizer Statistics Parameters”
</a>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
TABLESPACE
</code>
</p>
<p>
The
<code class="literal">
TABLESPACE
</code>
clause can be used to create
an
<a class="link" href="innodb-storage-engine.html" title="Chapter 17 The InnoDB Storage Engine">
<code class="literal">
InnoDB
</code>
</a>
table in an existing
general tablespace, a file-per-table tablespace, or the system
tablespace.
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa19065397"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> <em class="replaceable">tbl_name</em> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span> <span class="token keyword">TABLESPACE</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> <em class="replaceable">tablespace_name</em></code></pre>
</div>
<p>
The general tablespace that you specify must exist prior to
using the
<code class="literal">
TABLESPACE
</code>
clause. For
information about general tablespaces, see
<a class="xref" href="general-tablespaces.html" title="17.6.3.3 General Tablespaces">
Section 17.6.3.3, “General Tablespaces”
</a>
.
</p>
<p>
The
<code class="literal">
<em class="replaceable">
<code>
tablespace_name
</code>
</em>
</code>
is a case-sensitive identifier. It may be quoted or unquoted.
The forward slash character (
<span class="quote">
“
<span class="quote">
/
</span>
”
</span>
) is not
permitted. Names beginning with
<span class="quote">
“
<span class="quote">
innodb_
</span>
”
</span>
are
reserved for special use.
</p>
<p>
To create a table in the system tablespace, specify
<code class="literal">
innodb_system
</code>
as the tablespace name.
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa13277967"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> <em class="replaceable">tbl_name</em> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span> <span class="token keyword">TABLESPACE</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> innodb_system</code></pre>
</div>
<p>
Using
<code class="literal">
TABLESPACE [=] innodb_system
</code>
, you can
place a table of any uncompressed row format in the system
tablespace regardless of the
<a class="link" href="innodb-parameters.html#sysvar_innodb_file_per_table">
<code class="literal">
innodb_file_per_table
</code>
</a>
setting. For example, you can add a table with
<code class="literal">
ROW_FORMAT=DYNAMIC
</code>
to the system tablespace
using
<code class="literal">
TABLESPACE [=] innodb_system
</code>
.
</p>
<p>
To create a table in a file-per-table tablespace, specify
<code class="literal">
innodb_file_per_table
</code>
as the tablespace
name.
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa71405264"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> <em class="replaceable">tbl_name</em> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span> <span class="token keyword">TABLESPACE</span> <span class="token punctuation">[</span><span class="token operator">=</span><span class="token punctuation">]</span> innodb_file_per_table</code></pre>
</div>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
If
<a class="link" href="innodb-parameters.html#sysvar_innodb_file_per_table">
<code class="literal">
innodb_file_per_table
</code>
</a>
is
enabled, you need not specify
<code class="literal">
TABLESPACE=innodb_file_per_table
</code>
to
create an
<code class="literal">
InnoDB
</code>
file-per-table
tablespace.
<code class="literal">
InnoDB
</code>
tables are created in
file-per-table tablespaces by default when
<a class="link" href="innodb-parameters.html#sysvar_innodb_file_per_table">
<code class="literal">
innodb_file_per_table
</code>
</a>
is
enabled.
</p>
</div>
<p>
The
<code class="literal">
DATA DIRECTORY
</code>
clause is permitted with
<code class="literal">
CREATE TABLE ...
TABLESPACE=innodb_file_per_table
</code>
but is otherwise
not supported for use in combination with the
<code class="literal">
TABLESPACE
</code>
clause. The directory specified
in a
<code class="literal">
DATA DIRECTORY
</code>
clause must be known to
<code class="literal">
InnoDB
</code>
. For more information, see
<a class="xref" href="innodb-create-table-external.html#innodb-create-table-external-data-directory" title="Using the DATA DIRECTORY Clause">
Using the DATA DIRECTORY Clause
</a>
.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
Support for
<code class="literal">
TABLESPACE =
innodb_file_per_table
</code>
and
<code class="literal">
TABLESPACE =
innodb_temporary
</code>
clauses with
<a class="link" href="create-table.html" title="15.1.20 CREATE TABLE Statement">
<code class="literal">
CREATE
TEMPORARY TABLE
</code>
</a>
is deprecated; expect it to be
removed in a future version of MySQL.
</p>
</div>
<p>
The
<code class="literal">
STORAGE
</code>
table option is employed only
with
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDB
</code>
</a>
tables.
<code class="literal">
STORAGE
</code>
determines the type of storage
used, and can be either of
<code class="literal">
DISK
</code>
or
<code class="literal">
MEMORY
</code>
.
</p>
<p>
<code class="literal">
TABLESPACE ... STORAGE DISK
</code>
assigns a table
to an NDB Cluster Disk Data tablespace.
<code class="literal">
STORAGE
DISK
</code>
cannot be used in
<code class="literal">
CREATE
TABLE
</code>
unless preceded by
<code class="literal">
TABLESPACE
</code>
<em class="replaceable">
<code>
tablespace_name
</code>
</em>
.
</p>
<p>
For
<code class="literal">
STORAGE MEMORY
</code>
, the tablespace name is
optional, thus, you can use
<code class="literal">
TABLESPACE
<em class="replaceable">
<code>
tablespace_name
</code>
</em>
STORAGE
MEMORY
</code>
or simply
<code class="literal">
STORAGE MEMORY
</code>
to specify explicitly that the table is in-memory.
</p>
<p>
See
<a class="xref" href="mysql-cluster-disk-data.html" title="25.6.11 NDB Cluster Disk Data Tables">
Section 25.6.11, “NDB Cluster Disk Data Tables”
</a>
, for more
information.
</p>
</li>
<li class="listitem">
<p>
<a class="link" href="union.html" title="15.2.18 UNION Clause">
<code class="literal">
UNION
</code>
</a>
</p>
<p>
Used to access a collection of identical
<code class="literal">
MyISAM
</code>
tables as one. This works only with
<code class="literal">
MERGE
</code>
tables. See
<a class="xref" href="merge-storage-engine.html" title="18.7 The MERGE Storage Engine">
Section 18.7, “The MERGE Storage Engine”
</a>
.
</p>
<p>
You must have
<a class="link" href="privileges-provided.html#priv_select">
<code class="literal">
SELECT
</code>
</a>
,
<a class="link" href="privileges-provided.html#priv_update">
<code class="literal">
UPDATE
</code>
</a>
, and
<a class="link" href="privileges-provided.html#priv_delete">
<code class="literal">
DELETE
</code>
</a>
privileges for the
tables you map to a
<code class="literal">
MERGE
</code>
table.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
Formerly, all tables used had to be in the same database as
the
<code class="literal">
MERGE
</code>
table itself. This restriction
no longer applies.
</p>
</div>
</li>
</ul>
</div>
<h4>
<a name="create-table-partitioning">
</a>
Table Partitioning
</h4>
<p>
<em class="replaceable">
<code>
partition_options
</code>
</em>
can be used to
control partitioning of the table created with
<a class="link" href="create-table.html" title="15.1.20 CREATE TABLE Statement">
<code class="literal">
CREATE TABLE
</code>
</a>
.
</p>
<p>
Not all options shown in the syntax for
<em class="replaceable">
<code>
partition_options
</code>
</em>
at the beginning of
this section are available for all partitioning types. Please see
the listings for the following individual types for information
specific to each type, and see
<a class="xref" href="partitioning.html" title="Chapter 26 Partitioning">
Chapter 26,
<i>
Partitioning
</i>
</a>
, for
more complete information about the workings of and uses for
partitioning in MySQL, as well as additional examples of table
creation and other statements relating to MySQL partitioning.
</p>
<p>
Partitions can be modified, merged, added to tables, and dropped
from tables. For basic information about the MySQL statements to
accomplish these tasks, see
<a class="xref" href="alter-table.html" title="15.1.9 ALTER TABLE Statement">
Section 15.1.9, “ALTER TABLE Statement”
</a>
. For
more detailed descriptions and examples, see
<a class="xref" href="partitioning-management.html" title="26.3 Partition Management">
Section 26.3, “Partition Management”
</a>
.
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<code class="literal">
PARTITION BY
</code>
</p>
<p>
If used, a
<em class="replaceable">
<code>
partition_options
</code>
</em>
clause
begins with
<code class="literal">
PARTITION BY
</code>
. This clause
contains the function that is used to determine the partition;
the function returns an integer value ranging from 1 to
<em class="replaceable">
<code>
num
</code>
</em>
, where
<em class="replaceable">
<code>
num
</code>
</em>
is the number of partitions.
(The maximum number of user-defined partitions which a table
may contain is 1024; the number of
subpartitions—discussed later in this section—is
included in this maximum.)
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
The expression (
<em class="replaceable">
<code>
expr
</code>
</em>
) used in a
<code class="literal">
PARTITION BY
</code>
clause cannot refer to any
columns not in the table being created; such references are
specifically not permitted and cause the statement to fail
with an error. (Bug #29444)
</p>
</div>
</li>
<li class="listitem">
<p>
<code class="literal">
HASH(
<em class="replaceable">
<code>
expr
</code>
</em>
)
</code>
</p>
<p>
Hashes one or more columns to create a key for placing and
locating rows.
<em class="replaceable">
<code>
expr
</code>
</em>
is an
expression using one or more table columns. This can be any
valid MySQL expression (including MySQL functions) that yields
a single integer value. For example, these are both valid
<a class="link" href="create-table.html" title="15.1.20 CREATE TABLE Statement">
<code class="literal">
CREATE TABLE
</code>
</a>
statements using
<code class="literal">
PARTITION BY HASH
</code>
:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa91094464"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> t1 <span class="token punctuation">(</span>col1 <span class="token datatype">INT</span><span class="token punctuation">,</span> col2 <span class="token datatype">CHAR</span><span class="token punctuation">(</span><span class="token number">5</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
<span class="token keyword">PARTITION</span> <span class="token keyword">BY</span> <span class="token keyword">HASH</span><span class="token punctuation">(</span>col1<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> t1 <span class="token punctuation">(</span>col1 <span class="token datatype">INT</span><span class="token punctuation">,</span> col2 <span class="token datatype">CHAR</span><span class="token punctuation">(</span><span class="token number">5</span><span class="token punctuation">)</span><span class="token punctuation">,</span> col3 <span class="token datatype">DATETIME</span><span class="token punctuation">)</span>
<span class="token keyword">PARTITION</span> <span class="token keyword">BY</span> <span class="token keyword">HASH</span> <span class="token punctuation">(</span> <span class="token function">YEAR</span><span class="token punctuation">(</span>col3<span class="token punctuation">)</span> <span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
You may not use either
<code class="literal">
VALUES LESS THAN
</code>
or
<code class="literal">
VALUES IN
</code>
clauses with
<code class="literal">
PARTITION
BY HASH
</code>
.
</p>
<p>
<code class="literal">
PARTITION BY HASH
</code>
uses the remainder of
<em class="replaceable">
<code>
expr
</code>
</em>
divided by the number of
partitions (that is, the modulus). For examples and additional
information, see
<a class="xref" href="partitioning-hash.html" title="26.2.4 HASH Partitioning">
Section 26.2.4, “HASH Partitioning”
</a>
.
</p>
<p>
The
<code class="literal">
LINEAR
</code>
keyword entails a somewhat
different algorithm. In this case, the number of the partition
in which a row is stored is calculated as the result of one or
more logical
<a class="link" href="logical-operators.html#operator_and">
<code class="literal">
AND
</code>
</a>
operations. For
discussion and examples of linear hashing, see
<a class="xref" href="partitioning-linear-hash.html" title="26.2.4.1 LINEAR HASH Partitioning">
Section 26.2.4.1, “LINEAR HASH Partitioning”
</a>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
KEY(
<em class="replaceable">
<code>
column_list
</code>
</em>
)
</code>
</p>
<p>
This is similar to
<code class="literal">
HASH
</code>
, except that MySQL
supplies the hashing function so as to guarantee an even data
distribution. The
<em class="replaceable">
<code>
column_list
</code>
</em>
argument is simply a list of 1 or more table columns (maximum:
16). This example shows a simple table partitioned by key,
with 4 partitions:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa51188384"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> tk <span class="token punctuation">(</span>col1 <span class="token datatype">INT</span><span class="token punctuation">,</span> col2 <span class="token datatype">CHAR</span><span class="token punctuation">(</span><span class="token number">5</span><span class="token punctuation">)</span><span class="token punctuation">,</span> col3 <span class="token datatype">DATE</span><span class="token punctuation">)</span>
<span class="token keyword">PARTITION</span> <span class="token keyword">BY</span> <span class="token keyword">KEY</span><span class="token punctuation">(</span>col3<span class="token punctuation">)</span>
<span class="token keyword">PARTITIONS</span> <span class="token number">4</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
For tables that are partitioned by key, you can employ linear
partitioning by using the
<code class="literal">
LINEAR
</code>
keyword.
This has the same effect as with tables that are partitioned
by
<code class="literal">
HASH
</code>
. That is, the partition number is
found using the
<a class="link" href="bit-functions.html#operator_bitwise-and">
<code class="literal">
&
</code>
</a>
operator rather than the modulus (see
<a class="xref" href="partitioning-linear-hash.html" title="26.2.4.1 LINEAR HASH Partitioning">
Section 26.2.4.1, “LINEAR HASH Partitioning”
</a>
, and
<a class="xref" href="partitioning-key.html" title="26.2.5 KEY Partitioning">
Section 26.2.5, “KEY Partitioning”
</a>
, for details). This example
uses linear partitioning by key to distribute data between 5
partitions:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa7230228"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> tk <span class="token punctuation">(</span>col1 <span class="token datatype">INT</span><span class="token punctuation">,</span> col2 <span class="token datatype">CHAR</span><span class="token punctuation">(</span><span class="token number">5</span><span class="token punctuation">)</span><span class="token punctuation">,</span> col3 <span class="token datatype">DATE</span><span class="token punctuation">)</span>
<span class="token keyword">PARTITION</span> <span class="token keyword">BY</span> <span class="token keyword">LINEAR</span> <span class="token keyword">KEY</span><span class="token punctuation">(</span>col3<span class="token punctuation">)</span>
<span class="token keyword">PARTITIONS</span> <span class="token number">5</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
The
<code class="literal">
ALGORITHM={1 | 2}
</code>
option is supported
with
<code class="literal">
[SUB]PARTITION BY [LINEAR] KEY
</code>
.
<code class="literal">
ALGORITHM=1
</code>
causes the server to use the
same key-hashing functions as MySQL 5.1;
<code class="literal">
ALGORITHM=2
</code>
means that the server employs
the key-hashing functions implemented and used by default for
new
<code class="literal">
KEY
</code>
partitioned tables in MySQL 5.5 and
later. (Partitioned tables created with the key-hashing
functions employed in MySQL 5.5 and later cannot be used by a
MySQL 5.1 server.) Not specifying the option has the same
effect as using
<code class="literal">
ALGORITHM=2
</code>
. This option is
intended for use chiefly when upgrading or downgrading
<code class="literal">
[LINEAR] KEY
</code>
partitioned tables between
MySQL 5.1 and later MySQL versions, or for creating tables
partitioned by
<code class="literal">
KEY
</code>
or
<code class="literal">
LINEAR
KEY
</code>
on a MySQL 5.5 or later server which can be used
on a MySQL 5.1 server. For more information, see
<a class="xref" href="alter-table-partition-operations.html" title="15.1.9.1 ALTER TABLE Partition Operations">
Section 15.1.9.1, “ALTER TABLE Partition Operations”
</a>
.
</p>
<p>
<a class="link" href="mysqldump.html" title="6.5.4 mysqldump — A Database Backup Program">
<span class="command">
<strong>
mysqldump
</strong>
</span>
</a>
writes this option encased in
versioned comments.
</p>
<p>
<code class="literal">
ALGORITHM=1
</code>
is shown when necessary in the
output of
<a class="link" href="show-create-table.html" title="15.7.7.11 SHOW CREATE TABLE Statement">
<code class="literal">
SHOW CREATE TABLE
</code>
</a>
using versioned comments in the same manner as
<a class="link" href="mysqldump.html" title="6.5.4 mysqldump — A Database Backup Program">
<span class="command">
<strong>
mysqldump
</strong>
</span>
</a>
.
<code class="literal">
ALGORITHM=2
</code>
is always omitted from
<code class="literal">
SHOW CREATE TABLE
</code>
output, even if this option was specified when creating the
original table.
</p>
<p>
You may not use either
<code class="literal">
VALUES LESS THAN
</code>
or
<code class="literal">
VALUES IN
</code>
clauses with
<code class="literal">
PARTITION
BY KEY
</code>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
RANGE(
<em class="replaceable">
<code>
expr
</code>
</em>
)
</code>
</p>
<p>
In this case,
<em class="replaceable">
<code>
expr
</code>
</em>
shows a range of
values using a set of
<code class="literal">
VALUES LESS THAN
</code>
operators. When using range partitioning, you must define at
least one partition using
<code class="literal">
VALUES LESS THAN
</code>
.
You cannot use
<code class="literal">
VALUES IN
</code>
with range
partitioning.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
For tables partitioned by
<code class="literal">
RANGE
</code>
,
<code class="literal">
VALUES LESS THAN
</code>
must be used with either
an integer literal value or an expression that evaluates to
a single integer value. In MySQL 8.4, you can
overcome this limitation in a table that is defined using
<code class="literal">
PARTITION BY RANGE COLUMNS
</code>
, as described
later in this section.
</p>
</div>
<p>
Suppose that you have a table that you wish to partition on a
column containing year values, according to the following
scheme.
</p>
<div class="informaltable">
<table summary="A table partitioning scheme based on a column containing year values, as described in the preceding text. The table lists partition numbers and corresponding range of years.">
<colgroup>
<col style="width: 40%"/>
<col style="width: 60%"/>
</colgroup>
<thead>
<tr>
<th>
Partition Number:
</th>
<th>
Years Range:
</th>
</tr>
</thead>
<tbody>
<tr>
<td>
0
</td>
<td>
1990 and earlier
</td>
</tr>
<tr>
<td>
1
</td>
<td>
1991 to 1994
</td>
</tr>
<tr>
<td>
2
</td>
<td>
1995 to 1998
</td>
</tr>
<tr>
<td>
3
</td>
<td>
1999 to 2002
</td>
</tr>
<tr>
<td>
4
</td>
<td>
2003 to 2005
</td>
</tr>
<tr>
<td>
5
</td>
<td>
2006 and later
</td>
</tr>
</tbody>
</table>
</div>
<p>
A table implementing such a partitioning scheme can be
realized by the
<a class="link" href="create-table.html" title="15.1.20 CREATE TABLE Statement">
<code class="literal">
CREATE TABLE
</code>
</a>
statement shown here:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa56828750"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> t1 <span class="token punctuation">(</span>
year_col <span class="token datatype">INT</span><span class="token punctuation">,</span>
some_data <span class="token datatype">INT</span>
<span class="token punctuation">)</span>
<span class="token keyword">PARTITION</span> <span class="token keyword">BY</span> <span class="token keyword">RANGE</span> <span class="token punctuation">(</span>year_col<span class="token punctuation">)</span> <span class="token punctuation">(</span>
<span class="token keyword">PARTITION</span> p0 <span class="token keyword">VALUES</span> <span class="token keyword">LESS</span> <span class="token keyword">THAN</span> <span class="token punctuation">(</span><span class="token number">1991</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
<span class="token keyword">PARTITION</span> p1 <span class="token keyword">VALUES</span> <span class="token keyword">LESS</span> <span class="token keyword">THAN</span> <span class="token punctuation">(</span><span class="token number">1995</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
<span class="token keyword">PARTITION</span> p2 <span class="token keyword">VALUES</span> <span class="token keyword">LESS</span> <span class="token keyword">THAN</span> <span class="token punctuation">(</span><span class="token number">1999</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
<span class="token keyword">PARTITION</span> p3 <span class="token keyword">VALUES</span> <span class="token keyword">LESS</span> <span class="token keyword">THAN</span> <span class="token punctuation">(</span><span class="token number">2002</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
<span class="token keyword">PARTITION</span> p4 <span class="token keyword">VALUES</span> <span class="token keyword">LESS</span> <span class="token keyword">THAN</span> <span class="token punctuation">(</span><span class="token number">2006</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
<span class="token keyword">PARTITION</span> p5 <span class="token keyword">VALUES</span> <span class="token keyword">LESS</span> <span class="token keyword">THAN</span> <span class="token keyword">MAXVALUE</span>
<span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
<code class="literal">
PARTITION ... VALUES LESS THAN ...
</code>
statements work in a consecutive fashion.
<code class="literal">
VALUES LESS
THAN MAXVALUE
</code>
works to specify
<span class="quote">
“
<span class="quote">
leftover
</span>
”
</span>
values that are greater than the
maximum value otherwise specified.
</p>
<p>
<code class="literal">
VALUES LESS THAN
</code>
clauses work sequentially
in a manner similar to that of the
<code class="literal">
case
</code>
portions of a
<code class="literal">
switch ... case
</code>
block (as
found in many programming languages such as C, Java, and PHP).
That is, the clauses must be arranged in such a way that the
upper limit specified in each successive
<code class="literal">
VALUES LESS
THAN
</code>
is greater than that of the previous one, with
the one referencing
<code class="literal">
MAXVALUE
</code>
coming last of
all in the list.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
RANGE
COLUMNS(
<em class="replaceable">
<code>
column_list
</code>
</em>
)
</code>
</p>
<p>
This variant on
<code class="literal">
RANGE
</code>
facilitates partition
pruning for queries using range conditions on multiple columns
(that is, having conditions such as
<code class="literal">
WHERE a = 1 AND b
< 10
</code>
or
<code class="literal">
WHERE a = 1 AND b = 10 AND c
< 10
</code>
). It enables you to specify value ranges in
multiple columns by using a list of columns in the
<code class="literal">
COLUMNS
</code>
clause and a set of column values
in each
<code class="literal">
PARTITION ... VALUES LESS THAN
(
<em class="replaceable">
<code>
value_list
</code>
</em>
)
</code>
partition
definition clause. (In the simplest case, this set consists of
a single column.) The maximum number of columns that can be
referenced in the
<em class="replaceable">
<code>
column_list
</code>
</em>
and
<em class="replaceable">
<code>
value_list
</code>
</em>
is 16.
</p>
<p>
The
<em class="replaceable">
<code>
column_list
</code>
</em>
used in the
<code class="literal">
COLUMNS
</code>
clause may contain only names of
columns; each column in the list must be one of the following
MySQL data types: the integer types; the string types; and
time or date column types. Columns using
<code class="literal">
BLOB
</code>
,
<code class="literal">
TEXT
</code>
,
<code class="literal">
SET
</code>
,
<code class="literal">
ENUM
</code>
,
<code class="literal">
BIT
</code>
, or spatial data types are not
permitted; columns that use floating-point number types are
also not permitted. You also may not use functions or
arithmetic expressions in the
<code class="literal">
COLUMNS
</code>
clause.
</p>
<p>
The
<code class="literal">
VALUES LESS THAN
</code>
clause used in a
partition definition must specify a literal value for each
column that appears in the
<code class="literal">
COLUMNS()
</code>
clause; that is, the list of values used for each
<code class="literal">
VALUES LESS THAN
</code>
clause must contain the
same number of values as there are columns listed in the
<code class="literal">
COLUMNS
</code>
clause. An attempt to use more or
fewer values in a
<code class="literal">
VALUES LESS THAN
</code>
clause
than there are in the
<code class="literal">
COLUMNS
</code>
clause causes
the statement to fail with the error
<span class="errortext">
Inconsistency
in usage of column lists for partitioning...
</span>
. You
cannot use
<code class="literal">
NULL
</code>
for any value appearing in
<code class="literal">
VALUES LESS THAN
</code>
. It is possible to use
<code class="literal">
MAXVALUE
</code>
more than once for a given column
other than the first, as shown in this example:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa22010538"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> rc <span class="token punctuation">(</span>
a <span class="token datatype">INT</span> <span class="token operator">NOT</span> <span class="token boolean">NULL</span><span class="token punctuation">,</span>
b <span class="token datatype">INT</span> <span class="token operator">NOT</span> <span class="token boolean">NULL</span>
<span class="token punctuation">)</span>
<span class="token keyword">PARTITION</span> <span class="token keyword">BY</span> <span class="token keyword">RANGE</span> <span class="token keyword">COLUMNS</span><span class="token punctuation">(</span>a<span class="token punctuation">,</span>b<span class="token punctuation">)</span> <span class="token punctuation">(</span>
<span class="token keyword">PARTITION</span> p0 <span class="token keyword">VALUES</span> <span class="token keyword">LESS</span> <span class="token keyword">THAN</span> <span class="token punctuation">(</span><span class="token number">10</span><span class="token punctuation">,</span><span class="token number">5</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
<span class="token keyword">PARTITION</span> p1 <span class="token keyword">VALUES</span> <span class="token keyword">LESS</span> <span class="token keyword">THAN</span> <span class="token punctuation">(</span><span class="token number">20</span><span class="token punctuation">,</span><span class="token number">10</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
<span class="token keyword">PARTITION</span> p2 <span class="token keyword">VALUES</span> <span class="token keyword">LESS</span> <span class="token keyword">THAN</span> <span class="token punctuation">(</span><span class="token number">50</span><span class="token punctuation">,</span><span class="token keyword">MAXVALUE</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
<span class="token keyword">PARTITION</span> p3 <span class="token keyword">VALUES</span> <span class="token keyword">LESS</span> <span class="token keyword">THAN</span> <span class="token punctuation">(</span><span class="token number">65</span><span class="token punctuation">,</span><span class="token keyword">MAXVALUE</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
<span class="token keyword">PARTITION</span> p4 <span class="token keyword">VALUES</span> <span class="token keyword">LESS</span> <span class="token keyword">THAN</span> <span class="token punctuation">(</span><span class="token keyword">MAXVALUE</span><span class="token punctuation">,</span><span class="token keyword">MAXVALUE</span><span class="token punctuation">)</span>
<span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
Each value used in a
<code class="literal">
VALUES LESS THAN
</code>
value
list must match the type of the corresponding column exactly;
no conversion is made. For example, you cannot use the string
<code class="literal">
'1'
</code>
for a value that matches a column that
uses an integer type (you must use the numeral
<code class="literal">
1
</code>
instead), nor can you use the numeral
<code class="literal">
1
</code>
for a value that matches a column that
uses a string type (in such a case, you must use a quoted
string:
<code class="literal">
'1'
</code>
).
</p>
<p>
For more information, see
<a class="xref" href="partitioning-range.html" title="26.2.1 RANGE Partitioning">
Section 26.2.1, “RANGE Partitioning”
</a>
, and
<a class="xref" href="partitioning-pruning.html" title="26.4 Partition Pruning">
Section 26.4, “Partition Pruning”
</a>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
LIST(
<em class="replaceable">
<code>
expr
</code>
</em>
)
</code>
</p>
<p>
This is useful when assigning partitions based on a table
column with a restricted set of possible values, such as a
state or country code. In such a case, all rows pertaining to
a certain state or country can be assigned to a single
partition, or a partition can be reserved for a certain set of
states or countries. It is similar to
<code class="literal">
RANGE
</code>
, except that only
<code class="literal">
VALUES
IN
</code>
may be used to specify permissible values for
each partition.
</p>
<p>
<code class="literal">
VALUES IN
</code>
is used with a list of values to
be matched. For instance, you could create a partitioning
scheme such as the following:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa66858137"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> client_firms <span class="token punctuation">(</span>
id <span class="token datatype">INT</span><span class="token punctuation">,</span>
<span class="token keyword">name</span> <span class="token datatype">VARCHAR</span><span class="token punctuation">(</span><span class="token number">35</span><span class="token punctuation">)</span>
<span class="token punctuation">)</span>
<span class="token keyword">PARTITION</span> <span class="token keyword">BY</span> <span class="token keyword">LIST</span> <span class="token punctuation">(</span>id<span class="token punctuation">)</span> <span class="token punctuation">(</span>
<span class="token keyword">PARTITION</span> r0 <span class="token keyword">VALUES</span> <span class="token keyword">IN</span> <span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">5</span><span class="token punctuation">,</span> <span class="token number">9</span><span class="token punctuation">,</span> <span class="token number">13</span><span class="token punctuation">,</span> <span class="token number">17</span><span class="token punctuation">,</span> <span class="token number">21</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
<span class="token keyword">PARTITION</span> r1 <span class="token keyword">VALUES</span> <span class="token keyword">IN</span> <span class="token punctuation">(</span><span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">6</span><span class="token punctuation">,</span> <span class="token number">10</span><span class="token punctuation">,</span> <span class="token number">14</span><span class="token punctuation">,</span> <span class="token number">18</span><span class="token punctuation">,</span> <span class="token number">22</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
<span class="token keyword">PARTITION</span> r2 <span class="token keyword">VALUES</span> <span class="token keyword">IN</span> <span class="token punctuation">(</span><span class="token number">3</span><span class="token punctuation">,</span> <span class="token number">7</span><span class="token punctuation">,</span> <span class="token number">11</span><span class="token punctuation">,</span> <span class="token number">15</span><span class="token punctuation">,</span> <span class="token number">19</span><span class="token punctuation">,</span> <span class="token number">23</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
<span class="token keyword">PARTITION</span> r3 <span class="token keyword">VALUES</span> <span class="token keyword">IN</span> <span class="token punctuation">(</span><span class="token number">4</span><span class="token punctuation">,</span> <span class="token number">8</span><span class="token punctuation">,</span> <span class="token number">12</span><span class="token punctuation">,</span> <span class="token number">16</span><span class="token punctuation">,</span> <span class="token number">20</span><span class="token punctuation">,</span> <span class="token number">24</span><span class="token punctuation">)</span>
<span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
When using list partitioning, you must define at least one
partition using
<code class="literal">
VALUES IN
</code>
. You cannot use
<code class="literal">
VALUES LESS THAN
</code>
with
<code class="literal">
PARTITION BY
LIST
</code>
.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
For tables partitioned by
<code class="literal">
LIST
</code>
, the value
list used with
<code class="literal">
VALUES IN
</code>
must consist of
integer values only. In MySQL 8.4, you can
overcome this limitation using partitioning by
<code class="literal">
LIST
COLUMNS
</code>
, which is described later in this section.
</p>
</div>
</li>
<li class="listitem">
<p>
<code class="literal">
LIST
COLUMNS(
<em class="replaceable">
<code>
column_list
</code>
</em>
)
</code>
</p>
<p>
This variant on
<code class="literal">
LIST
</code>
facilitates partition
pruning for queries using comparison conditions on multiple
columns (that is, having conditions such as
<code class="literal">
WHERE a =
5 AND b = 5
</code>
or
<code class="literal">
WHERE a = 1 AND b = 10 AND c
= 5
</code>
). It enables you to specify values in multiple
columns by using a list of columns in the
<code class="literal">
COLUMNS
</code>
clause and a set of column values
in each
<code class="literal">
PARTITION ... VALUES IN
(
<em class="replaceable">
<code>
value_list
</code>
</em>
)
</code>
partition
definition clause.
</p>
<p>
The rules governing regarding data types for the column list
used in
<code class="literal">
LIST
COLUMNS(
<em class="replaceable">
<code>
column_list
</code>
</em>
)
</code>
and
the value list used in
<code class="literal">
VALUES
IN(
<em class="replaceable">
<code>
value_list
</code>
</em>
)
</code>
are the
same as those for the column list used in
<code class="literal">
RANGE
COLUMNS(
<em class="replaceable">
<code>
column_list
</code>
</em>
)
</code>
and
the value list used in
<code class="literal">
VALUES LESS
THAN(
<em class="replaceable">
<code>
value_list
</code>
</em>
)
</code>
,
respectively, except that in the
<code class="literal">
VALUES IN
</code>
clause,
<code class="literal">
MAXVALUE
</code>
is not permitted, and you
may use
<code class="literal">
NULL
</code>
.
</p>
<p>
There is one important difference between the list of values
used for
<code class="literal">
VALUES IN
</code>
with
<code class="literal">
PARTITION
BY LIST COLUMNS
</code>
as opposed to when it is used with
<code class="literal">
PARTITION BY LIST
</code>
. When used with
<code class="literal">
PARTITION BY LIST COLUMNS
</code>
, each element in
the
<code class="literal">
VALUES IN
</code>
clause must be a
<span class="emphasis">
<em>
set
</em>
</span>
of column values; the number of
values in each set must be the same as the number of columns
used in the
<code class="literal">
COLUMNS
</code>
clause, and the data
types of these values must match those of the columns (and
occur in the same order). In the simplest case, the set
consists of a single column. The maximum number of columns
that can be used in the
<em class="replaceable">
<code>
column_list
</code>
</em>
and in the elements making up the
<em class="replaceable">
<code>
value_list
</code>
</em>
is 16.
</p>
<p>
The table defined by the following
<code class="literal">
CREATE
TABLE
</code>
statement provides an example of a table using
<code class="literal">
LIST COLUMNS
</code>
partitioning:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa38658655"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> lc <span class="token punctuation">(</span>
a <span class="token datatype">INT</span> <span class="token boolean">NULL</span><span class="token punctuation">,</span>
b <span class="token datatype">INT</span> <span class="token boolean">NULL</span>
<span class="token punctuation">)</span>
<span class="token keyword">PARTITION</span> <span class="token keyword">BY</span> <span class="token keyword">LIST</span> <span class="token keyword">COLUMNS</span><span class="token punctuation">(</span>a<span class="token punctuation">,</span>b<span class="token punctuation">)</span> <span class="token punctuation">(</span>
<span class="token keyword">PARTITION</span> p0 <span class="token keyword">VALUES</span> <span class="token keyword">IN</span><span class="token punctuation">(</span> <span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">,</span><span class="token number">0</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token punctuation">(</span><span class="token boolean">NULL</span><span class="token punctuation">,</span><span class="token boolean">NULL</span><span class="token punctuation">)</span> <span class="token punctuation">)</span><span class="token punctuation">,</span>
<span class="token keyword">PARTITION</span> p1 <span class="token keyword">VALUES</span> <span class="token keyword">IN</span><span class="token punctuation">(</span> <span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">,</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">,</span><span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">,</span><span class="token number">3</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span><span class="token number">2</span><span class="token punctuation">)</span> <span class="token punctuation">)</span><span class="token punctuation">,</span>
<span class="token keyword">PARTITION</span> p2 <span class="token keyword">VALUES</span> <span class="token keyword">IN</span><span class="token punctuation">(</span> <span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span><span class="token number">0</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token punctuation">(</span><span class="token number">2</span><span class="token punctuation">,</span><span class="token number">0</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token punctuation">(</span><span class="token number">2</span><span class="token punctuation">,</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token punctuation">(</span><span class="token number">3</span><span class="token punctuation">,</span><span class="token number">0</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token punctuation">(</span><span class="token number">3</span><span class="token punctuation">,</span><span class="token number">1</span><span class="token punctuation">)</span> <span class="token punctuation">)</span><span class="token punctuation">,</span>
<span class="token keyword">PARTITION</span> p3 <span class="token keyword">VALUES</span> <span class="token keyword">IN</span><span class="token punctuation">(</span> <span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span><span class="token number">3</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token punctuation">(</span><span class="token number">2</span><span class="token punctuation">,</span><span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token punctuation">(</span><span class="token number">2</span><span class="token punctuation">,</span><span class="token number">3</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token punctuation">(</span><span class="token number">3</span><span class="token punctuation">,</span><span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token punctuation">(</span><span class="token number">3</span><span class="token punctuation">,</span><span class="token number">3</span><span class="token punctuation">)</span> <span class="token punctuation">)</span>
<span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
</li>
<li class="listitem">
<p>
<code class="literal">
PARTITIONS
<em class="replaceable">
<code>
num
</code>
</em>
</code>
</p>
<p>
The number of partitions may optionally be specified with a
<code class="literal">
PARTITIONS
<em class="replaceable">
<code>
num
</code>
</em>
</code>
clause, where
<em class="replaceable">
<code>
num
</code>
</em>
is the number of
partitions. If both this clause
<span class="emphasis">
<em>
and
</em>
</span>
any
<code class="literal">
PARTITION
</code>
clauses are used,
<em class="replaceable">
<code>
num
</code>
</em>
must be equal to the total
number of any partitions that are declared using
<code class="literal">
PARTITION
</code>
clauses.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
Whether or not you use a
<code class="literal">
PARTITIONS
</code>
clause in creating a table that is partitioned by
<code class="literal">
RANGE
</code>
or
<code class="literal">
LIST
</code>
, you
must still include at least one
<code class="literal">
PARTITION
VALUES
</code>
clause in the table definition (see below).
</p>
</div>
</li>
<li class="listitem">
<p>
<code class="literal">
SUBPARTITION BY
</code>
</p>
<p>
A partition may optionally be divided into a number of
subpartitions. This can be indicated by using the optional
<code class="literal">
SUBPARTITION BY
</code>
clause. Subpartitioning may
be done by
<code class="literal">
HASH
</code>
or
<code class="literal">
KEY
</code>
.
Either of these may be
<code class="literal">
LINEAR
</code>
. These work
in the same way as previously described for the equivalent
partitioning types. (It is not possible to subpartition by
<code class="literal">
LIST
</code>
or
<code class="literal">
RANGE
</code>
.)
</p>
<p>
The number of subpartitions can be indicated using the
<code class="literal">
SUBPARTITIONS
</code>
keyword followed by an
integer value.
</p>
</li>
<li class="listitem">
<p>
Rigorous checking of the value used in
<code class="literal">
PARTITIONS
</code>
or
<code class="literal">
SUBPARTITIONS
</code>
clauses is applied and this
value must adhere to the following rules:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<p>
The value must be a positive, nonzero integer.
</p>
</li>
<li class="listitem">
<p>
No leading zeros are permitted.
</p>
</li>
<li class="listitem">
<p>
The value must be an integer literal, and cannot not be an
expression. For example,
<code class="literal">
PARTITIONS
0.2E+01
</code>
is not permitted, even though
<code class="literal">
0.2E+01
</code>
evaluates to
<code class="literal">
2
</code>
. (Bug #15890)
</p>
</li>
</ul>
</div>
</li>
<li class="listitem">
<p>
<code class="literal">
<em class="replaceable">
<code>
partition_definition
</code>
</em>
</code>
</p>
<p>
Each partition may be individually defined using a
<em class="replaceable">
<code>
partition_definition
</code>
</em>
clause. The
individual parts making up this clause are as follows:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<p>
<code class="literal">
PARTITION
<em class="replaceable">
<code>
partition_name
</code>
</em>
</code>
</p>
<p>
Specifies a logical name for the partition.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
VALUES
</code>
</p>
<p>
For range partitioning, each partition must include a
<code class="literal">
VALUES LESS THAN
</code>
clause; for list
partitioning, you must specify a
<code class="literal">
VALUES
IN
</code>
clause for each partition. This is used to
determine which rows are to be stored in this partition.
See the discussions of partitioning types in
<a class="xref" href="partitioning.html" title="Chapter 26 Partitioning">
Chapter 26,
<i>
Partitioning
</i>
</a>
, for syntax examples.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
[STORAGE] ENGINE
</code>
</p>
<p>
MySQL accepts a
<code class="literal">
[STORAGE] ENGINE
</code>
option
for both
<code class="literal">
PARTITION
</code>
and
<code class="literal">
SUBPARTITION
</code>
. Currently, the only way
in which this option can be used is to set all partitions
or all subpartitions to the same storage engine, and an
attempt to set different storage engines for partitions or
subpartitions in the same table raises the error
<span class="errortext">
ERROR 1469 (HY000): The mix of handlers in the
partitions is not permitted in this version of
MySQL
</span>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
COMMENT
</code>
</p>
<p>
An optional
<code class="literal">
COMMENT
</code>
clause may be used
to specify a string that describes the partition. Example:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa65739169"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">COMMENT</span> <span class="token operator">=</span> <span class="token string">'Data for the years previous to 1999'</span></code></pre>
</div>
<p>
The maximum length for a partition comment is 1024
characters.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
DATA DIRECTORY
</code>
and
<code class="literal">
INDEX
DIRECTORY
</code>
</p>
<p>
<code class="literal">
DATA DIRECTORY
</code>
and
<code class="literal">
INDEX
DIRECTORY
</code>
may be used to indicate the directory
where, respectively, the data and indexes for this
partition are to be stored. Both the
<code class="filename">
<em class="replaceable">
<code>
data_dir
</code>
</em>
</code>
and the
<code class="filename">
<em class="replaceable">
<code>
index_dir
</code>
</em>
</code>
must be absolute system path names.
</p>
<p>
The directory specified in a
<code class="literal">
DATA
DIRECTORY
</code>
clause must be known to
<code class="literal">
InnoDB
</code>
. For more information, see
<a class="xref" href="innodb-create-table-external.html#innodb-create-table-external-data-directory" title="Using the DATA DIRECTORY Clause">
Using the DATA DIRECTORY Clause
</a>
.
</p>
<p>
You must have the
<a class="link" href="privileges-provided.html#priv_file">
<code class="literal">
FILE
</code>
</a>
privilege to use the
<code class="literal">
DATA DIRECTORY
</code>
or
<code class="literal">
INDEX DIRECTORY
</code>
partition option.
</p>
<p>
Example:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa40237931"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> th <span class="token punctuation">(</span>id <span class="token datatype">INT</span><span class="token punctuation">,</span> <span class="token keyword">name</span> <span class="token datatype">VARCHAR</span><span class="token punctuation">(</span><span class="token number">30</span><span class="token punctuation">)</span><span class="token punctuation">,</span> adate <span class="token datatype">DATE</span><span class="token punctuation">)</span>
<span class="token keyword">PARTITION</span> <span class="token keyword">BY</span> <span class="token keyword">LIST</span><span class="token punctuation">(</span><span class="token function">YEAR</span><span class="token punctuation">(</span>adate<span class="token punctuation">)</span><span class="token punctuation">)</span>
<span class="token punctuation">(</span>
<span class="token keyword">PARTITION</span> p1999 <span class="token keyword">VALUES</span> <span class="token keyword">IN</span> <span class="token punctuation">(</span><span class="token number">1995</span><span class="token punctuation">,</span> <span class="token number">1999</span><span class="token punctuation">,</span> <span class="token number">2003</span><span class="token punctuation">)</span>
<span class="token keyword">DATA</span> <span class="token keyword">DIRECTORY</span> <span class="token operator">=</span> <span class="token string">'/var/appdata/95/data'</span>
<span class="token keyword">INDEX</span> <span class="token keyword">DIRECTORY</span> <span class="token operator">=</span> <span class="token string">'/var/appdata/95/idx'</span><span class="token punctuation">,</span>
<span class="token keyword">PARTITION</span> p2000 <span class="token keyword">VALUES</span> <span class="token keyword">IN</span> <span class="token punctuation">(</span><span class="token number">1996</span><span class="token punctuation">,</span> <span class="token number">2000</span><span class="token punctuation">,</span> <span class="token number">2004</span><span class="token punctuation">)</span>
<span class="token keyword">DATA</span> <span class="token keyword">DIRECTORY</span> <span class="token operator">=</span> <span class="token string">'/var/appdata/96/data'</span>
<span class="token keyword">INDEX</span> <span class="token keyword">DIRECTORY</span> <span class="token operator">=</span> <span class="token string">'/var/appdata/96/idx'</span><span class="token punctuation">,</span>
<span class="token keyword">PARTITION</span> p2001 <span class="token keyword">VALUES</span> <span class="token keyword">IN</span> <span class="token punctuation">(</span><span class="token number">1997</span><span class="token punctuation">,</span> <span class="token number">2001</span><span class="token punctuation">,</span> <span class="token number">2005</span><span class="token punctuation">)</span>
<span class="token keyword">DATA</span> <span class="token keyword">DIRECTORY</span> <span class="token operator">=</span> <span class="token string">'/var/appdata/97/data'</span>
<span class="token keyword">INDEX</span> <span class="token keyword">DIRECTORY</span> <span class="token operator">=</span> <span class="token string">'/var/appdata/97/idx'</span><span class="token punctuation">,</span>
<span class="token keyword">PARTITION</span> p2002 <span class="token keyword">VALUES</span> <span class="token keyword">IN</span> <span class="token punctuation">(</span><span class="token number">1998</span><span class="token punctuation">,</span> <span class="token number">2002</span><span class="token punctuation">,</span> <span class="token number">2006</span><span class="token punctuation">)</span>
<span class="token keyword">DATA</span> <span class="token keyword">DIRECTORY</span> <span class="token operator">=</span> <span class="token string">'/var/appdata/98/data'</span>
<span class="token keyword">INDEX</span> <span class="token keyword">DIRECTORY</span> <span class="token operator">=</span> <span class="token string">'/var/appdata/98/idx'</span>
<span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
<code class="literal">
DATA DIRECTORY
</code>
and
<code class="literal">
INDEX
DIRECTORY
</code>
behave in the same way as in the
<a class="link" href="create-table.html" title="15.1.20 CREATE TABLE Statement">
<code class="literal">
CREATE TABLE
</code>
</a>
statement's
<em class="replaceable">
<code>
table_option
</code>
</em>
clause as used for
<code class="literal">
MyISAM
</code>
tables.
</p>
<p>
One data directory and one index directory may be
specified per partition. If left unspecified, the data and
indexes are stored by default in the table's database
directory.
</p>
<p>
The
<code class="literal">
DATA DIRECTORY
</code>
and
<code class="literal">
INDEX
DIRECTORY
</code>
options are ignored for creating
partitioned tables if
<a class="link" href="sql-mode.html#sqlmode_no_dir_in_create">
<code class="literal">
NO_DIR_IN_CREATE
</code>
</a>
is in
effect.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
MAX_ROWS
</code>
and
<code class="literal">
MIN_ROWS
</code>
</p>
<p>
May be used to specify, respectively, the maximum and
minimum number of rows to be stored in the partition. The
values for
<em class="replaceable">
<code>
max_number_of_rows
</code>
</em>
and
<em class="replaceable">
<code>
min_number_of_rows
</code>
</em>
must be
positive integers. As with the table-level options with
the same names, these act only as
<span class="quote">
“
<span class="quote">
suggestions
</span>
”
</span>
to the server and are not hard
limits.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
TABLESPACE
</code>
</p>
<p>
May be used to designate an
<code class="literal">
InnoDB
</code>
file-per-table tablespace for the partition by specifying
<code class="literal">
TABLESPACE `innodb_file_per_table`
</code>
. All
partitions must belong to the same storage engine.
</p>
<p>
Placing
<code class="literal">
InnoDB
</code>
table partitions in
shared
<code class="literal">
InnoDB
</code>
tablespaces is not
supported. Shared tablespaces include the
<code class="literal">
InnoDB
</code>
system tablespace and general
tablespaces.
</p>
</li>
</ul>
</div>
</li>
<li class="listitem">
<p>
<code class="literal">
<em class="replaceable">
<code>
subpartition_definition
</code>
</em>
</code>
</p>
<p>
The partition definition may optionally contain one or more
<em class="replaceable">
<code>
subpartition_definition
</code>
</em>
clauses.
Each of these consists at a minimum of the
<code class="literal">
SUBPARTITION
<em class="replaceable">
<code>
name
</code>
</em>
</code>
, where
<em class="replaceable">
<code>
name
</code>
</em>
is an identifier for the
subpartition. Except for the replacement of the
<code class="literal">
PARTITION
</code>
keyword with
<code class="literal">
SUBPARTITION
</code>
, the syntax for a subpartition
definition is identical to that for a partition definition.
</p>
<p>
Subpartitioning must be done by
<code class="literal">
HASH
</code>
or
<code class="literal">
KEY
</code>
, and can be done only on
<code class="literal">
RANGE
</code>
or
<code class="literal">
LIST
</code>
partitions. See
<a class="xref" href="partitioning-subpartitions.html" title="26.2.6 Subpartitioning">
Section 26.2.6, “Subpartitioning”
</a>
.
</p>
</li>
</ul>
</div>
<p>
<span class="bold">
<strong>
Partitioning by Generated Columns
</strong>
</span>
</p>
<p>
Partitioning by generated columns is permitted. For example:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa92395403"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> t1 <span class="token punctuation">(</span>
s1 <span class="token datatype">INT</span><span class="token punctuation">,</span>
s2 <span class="token datatype">INT</span> <span class="token keyword">AS</span> <span class="token punctuation">(</span><span class="token function">EXP</span><span class="token punctuation">(</span>s1<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token keyword">STORED</span>
<span class="token punctuation">)</span>
<span class="token keyword">PARTITION</span> <span class="token keyword">BY</span> <span class="token keyword">LIST</span> <span class="token punctuation">(</span>s2<span class="token punctuation">)</span> <span class="token punctuation">(</span>
<span class="token keyword">PARTITION</span> p1 <span class="token keyword">VALUES</span> <span class="token keyword">IN</span> <span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span>
<span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
Partitioning sees a generated column as a regular column, which
enables workarounds for limitations on functions that are not
permitted for partitioning (see
<a class="xref" href="partitioning-limitations-functions.html" title="26.6.3 Partitioning Limitations Relating to Functions">
Section 26.6.3, “Partitioning Limitations Relating to Functions”
</a>
). The
preceding example demonstrates this technique:
<a class="link" href="mathematical-functions.html#function_exp">
<code class="literal">
EXP()
</code>
</a>
cannot be used directly in
the
<code class="literal">
PARTITION BY
</code>
clause, but a generated column
defined using
<a class="link" href="mathematical-functions.html#function_exp">
<code class="literal">
EXP()
</code>
</a>
is permitted.
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/replication-features-partitioning.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="replication-features-partitioning">
</a>
19.5.1.24 Replication and Partitioning
</h4>
</div>
</div>
</div>
<a class="indexterm" name="idm46045135252528">
</a>
<a class="indexterm" name="idm46045135251040">
</a>
<p>
Replication is supported between partitioned tables as long as
they use the same partitioning scheme and otherwise have the
same structure, except where an exception is specifically
allowed (see
<a class="xref" href="replication-features-differing-tables.html" title="19.5.1.9 Replication with Differing Table Definitions on Source and Replica">
Section 19.5.1.9, “Replication with Differing Table Definitions on Source and Replica”
</a>
).
</p>
<p>
Replication between tables that have different partitioning is
generally not supported. This because statements (such as
<a class="link" href="alter-table-partition-operations.html" title="15.1.9.1 ALTER TABLE Partition Operations">
<code class="literal">
ALTER
TABLE ... DROP PARTITION
</code>
</a>
) that act directly on
partitions in such cases might produce different results on the
source and the replica. In the case where a table is partitioned
on the source but not on the replica, any statements that
operate on partitions on the source's copy of the replica
fail on the replica. When the replica's copy of the table
is partitioned but the source's copy is not, statements
that act directly on partitions cannot be run on the source
without causing errors there. To avoid stopping replication or
creating inconsistencies between the source and replica, always
ensure that a table on the source and the corresponding
replicated table on the replica are partitioned in the same way.
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/values.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="values">
</a>
15.2.19 VALUES Statement
</h3>
</div>
</div>
</div>
<a class="indexterm" name="idm46045179322000">
</a>
<a class="indexterm" name="idm46045179320928">
</a>
<a class="indexterm" name="idm46045179319472">
</a>
<p>
<a class="link" href="values.html" title="15.2.19 VALUES Statement">
<code class="literal">
VALUES
</code>
</a>
is a DML statement which
returns a set of one or more rows as a table. In other words, it
is a table value constructor which also functions as a standalone
SQL statement.
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa36051782"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">VALUES</span> <em class="replaceable">row_constructor_list</em> <span class="token punctuation">[</span><span class="token keyword">ORDER</span> <span class="token keyword">BY</span> <em class="replaceable">column_designator</em><span class="token punctuation">]</span> <span class="token punctuation">[</span><span class="token keyword">LIMIT</span> <span class="token keyword"><em class="replaceable">number</em></span><span class="token punctuation">]</span>
<em class="replaceable">row_constructor_list</em>:
<span class="token keyword">ROW</span><span class="token punctuation">(</span><em class="replaceable">value_list</em><span class="token punctuation">)</span><span class="token punctuation">[</span><span class="token punctuation">,</span> <span class="token keyword">ROW</span><span class="token punctuation">(</span><em class="replaceable">value_list</em><span class="token punctuation">)</span><span class="token punctuation">]</span><span class="token punctuation">[</span><span class="token punctuation">,</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">]</span>
<em class="replaceable">value_list</em>:
<span class="token keyword"><em class="replaceable">value</em></span><span class="token punctuation">[</span><span class="token punctuation">,</span> <span class="token keyword"><em class="replaceable">value</em></span><span class="token punctuation">]</span><span class="token punctuation">[</span><span class="token punctuation">,</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">]</span>
<em class="replaceable">column_designator</em>:
column_<em class="replaceable">index</em></code></pre>
</div>
<p>
The
<a class="link" href="values.html" title="15.2.19 VALUES Statement">
<code class="literal">
VALUES
</code>
</a>
statement consists of
the
<code class="literal">
VALUES
</code>
keyword followed by a list of one or
more row constructors, separated by commas. A row constructor
consists of the
<code class="literal">
ROW()
</code>
row constructor clause
with a value list of one or more scalar values enclosed in the
parentheses. A value can be a literal of any MySQL data type or an
expression that resolves to a scalar value.
</p>
<p>
<code class="literal">
ROW()
</code>
cannot be empty (but each of the supplied
scalar values can be
<code class="literal">
NULL
</code>
). Each
<code class="literal">
ROW()
</code>
in the same
<a class="link" href="values.html" title="15.2.19 VALUES Statement">
<code class="literal">
VALUES
</code>
</a>
statement must have the same
number of values in its value list.
</p>
<p>
The
<code class="literal">
DEFAULT
</code>
keyword is not supported by
<code class="literal">
VALUES
</code>
and causes a syntax error, except when
it is used to supply values in an
<a class="link" href="insert.html" title="15.2.7 INSERT Statement">
<code class="literal">
INSERT
</code>
</a>
statement.
</p>
<p>
The output of
<a class="link" href="values.html" title="15.2.19 VALUES Statement">
<code class="literal">
VALUES
</code>
</a>
is a table:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa20194634"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">VALUES</span> <span class="token keyword">ROW</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span><span class="token operator">-</span><span class="token number">2</span><span class="token punctuation">,</span><span class="token number">3</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token keyword">ROW</span><span class="token punctuation">(</span><span class="token number">5</span><span class="token punctuation">,</span><span class="token number">7</span><span class="token punctuation">,</span><span class="token number">9</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token keyword">ROW</span><span class="token punctuation">(</span><span class="token number">4</span><span class="token punctuation">,</span><span class="token number">6</span><span class="token punctuation">,</span><span class="token number">8</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> column_0 <span class="token punctuation">|</span> column_1 <span class="token punctuation">|</span> column_2 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> 1 <span class="token punctuation">|</span> <span class="token punctuation">-</span>2 <span class="token punctuation">|</span> 3 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> 5 <span class="token punctuation">|</span> 7 <span class="token punctuation">|</span> 9 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> 4 <span class="token punctuation">|</span> 6 <span class="token punctuation">|</span> 8 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output">3 rows in set (0.00 sec)</span></code></pre>
</div>
<p>
The columns of the table output from
<a class="link" href="values.html" title="15.2.19 VALUES Statement">
<code class="literal">
VALUES
</code>
</a>
have the implicitly named
columns
<code class="literal">
column_0
</code>
,
<code class="literal">
column_1
</code>
,
<code class="literal">
column_2
</code>
, and so on, always beginning with
<code class="literal">
0
</code>
. This fact can be used to order the rows by
column using an optional
<code class="literal">
ORDER BY
</code>
clause in the
same way that this clause works with a
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT
</code>
</a>
statement, as shown here:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa29105761"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">VALUES</span> <span class="token keyword">ROW</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span><span class="token operator">-</span><span class="token number">2</span><span class="token punctuation">,</span><span class="token number">3</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token keyword">ROW</span><span class="token punctuation">(</span><span class="token number">5</span><span class="token punctuation">,</span><span class="token number">7</span><span class="token punctuation">,</span><span class="token number">9</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token keyword">ROW</span><span class="token punctuation">(</span><span class="token number">4</span><span class="token punctuation">,</span><span class="token number">6</span><span class="token punctuation">,</span><span class="token number">8</span><span class="token punctuation">)</span> <span class="token keyword">ORDER</span> <span class="token keyword">BY</span> column_1<span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> column_0 <span class="token punctuation">|</span> column_1 <span class="token punctuation">|</span> column_2 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> 1 <span class="token punctuation">|</span> <span class="token punctuation">-</span>2 <span class="token punctuation">|</span> 3 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> 4 <span class="token punctuation">|</span> 6 <span class="token punctuation">|</span> 8 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> 5 <span class="token punctuation">|</span> 7 <span class="token punctuation">|</span> 9 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output">3 rows in set (0.00 sec)</span></code></pre>
</div>
<p>
<a class="link" href="values.html" title="15.2.19 VALUES Statement">
<code class="literal">
VALUES
</code>
</a>
statement also supports a
<code class="literal">
LIMIT
</code>
clause for limiting the number of rows in
the output.
</p>
<p>
The
<code class="literal">
VALUES
</code>
statement is permissive regarding
data types of column values; you can mix types within the same
column, as shown here:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa89672478"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">VALUES</span> <span class="token keyword">ROW</span><span class="token punctuation">(</span><span class="token string">"q"</span><span class="token punctuation">,</span> <span class="token number">42</span><span class="token punctuation">,</span> <span class="token string">'2019-12-18'</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
<span class="token prompt"> -></span> <span class="token keyword">ROW</span><span class="token punctuation">(</span><span class="token number">23</span><span class="token punctuation">,</span> <span class="token string">"abc"</span><span class="token punctuation">,</span> <span class="token number">98.6</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
<span class="token prompt"> -></span> <span class="token keyword">ROW</span><span class="token punctuation">(</span><span class="token number">27.0002</span><span class="token punctuation">,</span> <span class="token string">"Mary Smith"</span><span class="token punctuation">,</span> <span class="token string">'{"a": 10, "b": 25}'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> column_0 <span class="token punctuation">|</span> column_1 <span class="token punctuation">|</span> column_2 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> q <span class="token punctuation">|</span> 42 <span class="token punctuation">|</span> 2019<span class="token punctuation">-</span>12<span class="token punctuation">-</span>18 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> 23 <span class="token punctuation">|</span> abc <span class="token punctuation">|</span> 98.6 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> 27.0002 <span class="token punctuation">|</span> Mary Smith <span class="token punctuation">|</span> {"a": 10, "b": 25} <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output">3 rows in set (0.00 sec)</span></code></pre>
</div>
<div class="important" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Important
</div>
<p>
<code class="literal">
VALUES
</code>
with one or more instances of
<code class="literal">
ROW()
</code>
acts as a table value constructor;
although it can be used to supply values in an
<a class="link" href="insert.html" title="15.2.7 INSERT Statement">
<code class="literal">
INSERT
</code>
</a>
or
<a class="link" href="replace.html" title="15.2.12 REPLACE Statement">
<code class="literal">
REPLACE
</code>
</a>
statement, do not confuse
it with the
<code class="literal">
VALUES
</code>
keyword that is also used
for this purpose. You should also not confuse it with the
<a class="link" href="miscellaneous-functions.html#function_values">
<code class="literal">
VALUES()
</code>
</a>
function that refers to
column values in
<a class="link" href="insert-on-duplicate.html" title="15.2.7.2 INSERT ... ON DUPLICATE KEY UPDATE Statement">
<code class="literal">
INSERT ...
ON DUPLICATE KEY UPDATE
</code>
</a>
.
</p>
<p>
You should also bear in mind that
<code class="literal">
ROW()
</code>
is a
row value constructor (see
<a class="xref" href="row-subqueries.html" title="15.2.15.5 Row Subqueries">
Section 15.2.15.5, “Row Subqueries”
</a>
),
whereas
<code class="literal">
VALUES ROW()
</code>
is a table value
constructor; the two cannot be used interchangeably.
</p>
</div>
<p>
<a class="link" href="values.html" title="15.2.19 VALUES Statement">
<code class="literal">
VALUES
</code>
</a>
can be used in many cases
where you could employ
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT
</code>
</a>
,
including those listed here:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
With
<a class="link" href="union.html" title="15.2.18 UNION Clause">
<code class="literal">
UNION
</code>
</a>
, as shown here:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa82562179"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token number">1</span><span class="token punctuation">,</span><span class="token number">2</span> <span class="token keyword">UNION</span> <span class="token keyword">SELECT</span> <span class="token number">10</span><span class="token punctuation">,</span><span class="token number">15</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> 1 <span class="token punctuation">|</span> 2 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> 1 <span class="token punctuation">|</span> 2 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> 10 <span class="token punctuation">|</span> 15 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output">2 rows in set (0.00 sec)</span>
<span class="token prompt">mysql></span> <span class="token keyword">VALUES</span> <span class="token keyword">ROW</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span><span class="token number">2</span><span class="token punctuation">)</span> <span class="token keyword">UNION</span> <span class="token keyword">VALUES</span> <span class="token keyword">ROW</span><span class="token punctuation">(</span><span class="token number">10</span><span class="token punctuation">,</span><span class="token number">15</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> column_0 <span class="token punctuation">|</span> column_1 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> 1 <span class="token punctuation">|</span> 2 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> 10 <span class="token punctuation">|</span> 15 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output">2 rows in set (0.00 sec)</span></code></pre>
</div>
<p>
You can union together constructed tables having more than one
row, like this:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa93961964"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">VALUES</span> <span class="token keyword">ROW</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span><span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token keyword">ROW</span><span class="token punctuation">(</span><span class="token number">3</span><span class="token punctuation">,</span><span class="token number">4</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token keyword">ROW</span><span class="token punctuation">(</span><span class="token number">5</span><span class="token punctuation">,</span><span class="token number">6</span><span class="token punctuation">)</span>
<span class="token operator">></span> <span class="token keyword">UNION</span> <span class="token keyword">VALUES</span> <span class="token keyword">ROW</span><span class="token punctuation">(</span><span class="token number">10</span><span class="token punctuation">,</span><span class="token number">15</span><span class="token punctuation">)</span><span class="token punctuation">,</span><span class="token keyword">ROW</span><span class="token punctuation">(</span><span class="token number">20</span><span class="token punctuation">,</span><span class="token number">25</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> column_0 <span class="token punctuation">|</span> column_1 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> 1 <span class="token punctuation">|</span> 2 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> 3 <span class="token punctuation">|</span> 4 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> 5 <span class="token punctuation">|</span> 6 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> 10 <span class="token punctuation">|</span> 15 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> 20 <span class="token punctuation">|</span> 25 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output">5 rows in set (0.00 sec)</span></code></pre>
</div>
<p>
You can also (and it is usually preferable to) omit
<a class="link" href="union.html" title="15.2.18 UNION Clause">
<code class="literal">
UNION
</code>
</a>
altogether in such cases
and use a single
<strong class="userinput">
<code>
VALUES
</code>
</strong>
statement, like
this:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa42975394"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">VALUES</span> <span class="token keyword">ROW</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span><span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token keyword">ROW</span><span class="token punctuation">(</span><span class="token number">3</span><span class="token punctuation">,</span><span class="token number">4</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token keyword">ROW</span><span class="token punctuation">(</span><span class="token number">5</span><span class="token punctuation">,</span><span class="token number">6</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token keyword">ROW</span><span class="token punctuation">(</span><span class="token number">10</span><span class="token punctuation">,</span><span class="token number">15</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token keyword">ROW</span><span class="token punctuation">(</span><span class="token number">20</span><span class="token punctuation">,</span><span class="token number">25</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> column_0 <span class="token punctuation">|</span> column_1 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> 1 <span class="token punctuation">|</span> 2 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> 3 <span class="token punctuation">|</span> 4 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> 5 <span class="token punctuation">|</span> 6 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> 10 <span class="token punctuation">|</span> 15 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> 20 <span class="token punctuation">|</span> 25 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span></code></pre>
</div>
<p>
<code class="literal">
VALUES
</code>
can also be used in unions with
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT
</code>
</a>
statements,
<a class="link" href="table.html" title="15.2.16 TABLE Statement">
<code class="literal">
TABLE
</code>
</a>
statements, or both.
</p>
<p>
The constructed tables in the
<a class="link" href="union.html" title="15.2.18 UNION Clause">
<code class="literal">
UNION
</code>
</a>
must contain the same
number of columns, just as if you were using
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT
</code>
</a>
. See
<a class="xref" href="union.html" title="15.2.18 UNION Clause">
Section 15.2.18, “UNION Clause”
</a>
, for further examples.
</p>
<p>
You can use
<a class="link" href="except.html" title="15.2.4 EXCEPT Clause">
<code class="literal">
EXCEPT
</code>
</a>
and
<a class="link" href="intersect.html" title="15.2.8 INTERSECT Clause">
<code class="literal">
INTERSECT
</code>
</a>
with
<code class="literal">
VALUES
</code>
in much the same way as
<code class="literal">
UNION
</code>
, as shown here:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa98282557"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">VALUES</span> <span class="token keyword">ROW</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span><span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token keyword">ROW</span><span class="token punctuation">(</span><span class="token number">3</span><span class="token punctuation">,</span><span class="token number">4</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token keyword">ROW</span><span class="token punctuation">(</span><span class="token number">5</span><span class="token punctuation">,</span><span class="token number">6</span><span class="token punctuation">)</span>
<span class="token prompt"> -></span> <span class="token keyword">INTERSECT</span>
<span class="token prompt"> -></span> <span class="token keyword">VALUES</span> <span class="token keyword">ROW</span><span class="token punctuation">(</span><span class="token number">10</span><span class="token punctuation">,</span><span class="token number">15</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token keyword">ROW</span><span class="token punctuation">(</span><span class="token number">20</span><span class="token punctuation">,</span><span class="token number">25</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token keyword">ROW</span><span class="token punctuation">(</span><span class="token number">3</span><span class="token punctuation">,</span><span class="token number">4</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> column_0 <span class="token punctuation">|</span> column_1 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> 3 <span class="token punctuation">|</span> 4 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output">1 row in set (0.00 sec)</span>
<span class="token prompt">mysql></span> <span class="token keyword">VALUES</span> <span class="token keyword">ROW</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span><span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token keyword">ROW</span><span class="token punctuation">(</span><span class="token number">3</span><span class="token punctuation">,</span><span class="token number">4</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token keyword">ROW</span><span class="token punctuation">(</span><span class="token number">5</span><span class="token punctuation">,</span><span class="token number">6</span><span class="token punctuation">)</span>
<span class="token prompt"> -></span> <span class="token keyword">EXCEPT</span>
<span class="token prompt"> -></span> <span class="token keyword">VALUES</span> <span class="token keyword">ROW</span><span class="token punctuation">(</span><span class="token number">10</span><span class="token punctuation">,</span><span class="token number">15</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token keyword">ROW</span><span class="token punctuation">(</span><span class="token number">20</span><span class="token punctuation">,</span><span class="token number">25</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token keyword">ROW</span><span class="token punctuation">(</span><span class="token number">3</span><span class="token punctuation">,</span><span class="token number">4</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> column_0 <span class="token punctuation">|</span> column_1 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> 1 <span class="token punctuation">|</span> 2 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> 5 <span class="token punctuation">|</span> 6 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output">2 rows in set (0.00 sec)</span></code></pre>
</div>
<p>
See
<a class="xref" href="except.html" title="15.2.4 EXCEPT Clause">
Section 15.2.4, “EXCEPT Clause”
</a>
, and
<a class="xref" href="intersect.html" title="15.2.8 INTERSECT Clause">
Section 15.2.8, “INTERSECT Clause”
</a>
,
for more information.
</p>
</li>
<li class="listitem">
<p>
In joins. See
<a class="xref" href="join.html" title="15.2.13.2 JOIN Clause">
Section 15.2.13.2, “JOIN Clause”
</a>
, for more information and
examples.
</p>
</li>
<li class="listitem">
<p>
In place of
<a class="link" href="miscellaneous-functions.html#function_values">
<code class="literal">
VALUES()
</code>
</a>
in an
<a class="link" href="insert.html" title="15.2.7 INSERT Statement">
<code class="literal">
INSERT
</code>
</a>
or
<a class="link" href="replace.html" title="15.2.12 REPLACE Statement">
<code class="literal">
REPLACE
</code>
</a>
statement, in which
case its semantics differ slightly from what is described
here. See
<a class="xref" href="insert.html" title="15.2.7 INSERT Statement">
Section 15.2.7, “INSERT Statement”
</a>
, for details.
</p>
</li>
<li class="listitem">
<p>
In place of the source table in
<a class="link" href="create-table-select.html" title="15.1.20.4 CREATE TABLE ... SELECT Statement">
<code class="literal">
CREATE
TABLE ... SELECT
</code>
</a>
and
<a class="link" href="create-view.html" title="15.1.23 CREATE VIEW Statement">
<code class="literal">
CREATE VIEW ...
SELECT
</code>
</a>
. See the descriptions of these statements for
more information and examples.
</p>
</li>
</ul>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/postinstallation.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h2 class="title">
<a name="postinstallation">
</a>
2.9 Postinstallation Setup and Testing
</h2>
</div>
</div>
</div>
<div class="toc">
<dl class="toc">
<dt>
<span class="section">
<a href="data-directory-initialization.html">
2.9.1 Initializing the Data Directory
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="starting-server.html">
2.9.2 Starting the Server
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="testing-server.html">
2.9.3 Testing the Server
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="default-privileges.html">
2.9.4 Securing the Initial MySQL Account
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="automatic-start.html">
2.9.5 Starting and Stopping MySQL Automatically
</a>
</span>
</dt>
</dl>
</div>
<a class="indexterm" name="idm46045327114784">
</a>
<a class="indexterm" name="idm46045327113328">
</a>
<a class="indexterm" name="idm46045327111840">
</a>
<p>
This section discusses tasks that you should perform after
installing MySQL:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
If necessary, initialize the data directory and create the MySQL
grant tables. For some MySQL installation methods, data
directory initialization may be done for you automatically:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<p>
Windows installation operations performed by the MSI
installer and MySQL Configurator.
</p>
</li>
<li class="listitem">
<p>
Installation on Linux using a server RPM or Debian
distribution from Oracle.
</p>
</li>
<li class="listitem">
<p>
Installation using the native packaging system on many
platforms, including Debian Linux, Ubuntu Linux, Gentoo
Linux, and others.
</p>
</li>
<li class="listitem">
<p>
Installation on macOS using a DMG distribution.
</p>
</li>
</ul>
</div>
<p>
For other platforms and installation types, you must initialize
the data directory manually. These include installation from
generic binary and source distributions on Unix and Unix-like
system, and installation from a ZIP Archive package on Windows.
For instructions, see
<a class="xref" href="data-directory-initialization.html" title="2.9.1 Initializing the Data Directory">
Section 2.9.1, “Initializing the Data Directory”
</a>
.
</p>
</li>
<li class="listitem">
<p>
Start the server and make sure that it can be accessed. For
instructions, see
<a class="xref" href="starting-server.html" title="2.9.2 Starting the Server">
Section 2.9.2, “Starting the Server”
</a>
, and
<a class="xref" href="testing-server.html" title="2.9.3 Testing the Server">
Section 2.9.3, “Testing the Server”
</a>
.
</p>
</li>
<li class="listitem">
<p>
Assign passwords to the initial
<code class="literal">
root
</code>
account
in the grant tables, if that was not already done during data
directory initialization. Passwords prevent unauthorized access
to the MySQL server. For instructions, see
<a class="xref" href="default-privileges.html" title="2.9.4 Securing the Initial MySQL Account">
Section 2.9.4, “Securing the Initial MySQL Account”
</a>
.
</p>
</li>
<li class="listitem">
<p>
Optionally, arrange for the server to start and stop
automatically when your system starts and stops. For
instructions, see
<a class="xref" href="automatic-start.html" title="2.9.5 Starting and Stopping MySQL Automatically">
Section 2.9.5, “Starting and Stopping MySQL Automatically”
</a>
.
</p>
</li>
<li class="listitem">
<p>
Optionally, populate time zone tables to enable recognition of
named time zones. For instructions, see
<a class="xref" href="time-zone-support.html" title="7.1.15 MySQL Server Time Zone Support">
Section 7.1.15, “MySQL Server Time Zone Support”
</a>
.
</p>
</li>
</ul>
</div>
<p>
When you are ready to create additional user accounts, you can find
information on the MySQL access control system and account
management in
<a class="xref" href="access-control.html" title="8.2 Access Control and Account Management">
Section 8.2, “Access Control and Account Management”
</a>
.
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/stored-routines-privileges.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="stored-routines-privileges">
</a>
27.2.2 Stored Routines and MySQL Privileges
</h3>
</div>
</div>
</div>
<p>
The MySQL grant system takes stored routines into account as
follows:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
The
<a class="link" href="privileges-provided.html#priv_create-routine">
<code class="literal">
CREATE ROUTINE
</code>
</a>
privilege is
needed to create stored routines.
</p>
</li>
<li class="listitem">
<p>
The
<a class="link" href="privileges-provided.html#priv_alter-routine">
<code class="literal">
ALTER ROUTINE
</code>
</a>
privilege is
needed to alter or drop stored routines. This privilege is
granted automatically to the creator of a routine if
necessary, and dropped from the creator when the routine is
dropped.
</p>
</li>
<li class="listitem">
<p>
The
<a class="link" href="privileges-provided.html#priv_execute">
<code class="literal">
EXECUTE
</code>
</a>
privilege is
required to execute stored routines. However, this privilege
is granted automatically to the creator of a routine if
necessary (and dropped from the creator when the routine is
dropped). Also, the default
<code class="literal">
SQL SECURITY
</code>
characteristic for a routine is
<code class="literal">
DEFINER
</code>
,
which enables users who have access to the database with which
the routine is associated to execute the routine.
</p>
</li>
<li class="listitem">
<p>
If the
<a class="link" href="server-system-variables.html#sysvar_automatic_sp_privileges">
<code class="literal">
automatic_sp_privileges
</code>
</a>
system variable is 0, the
<a class="link" href="privileges-provided.html#priv_execute">
<code class="literal">
EXECUTE
</code>
</a>
and
<a class="link" href="privileges-provided.html#priv_alter-routine">
<code class="literal">
ALTER ROUTINE
</code>
</a>
privileges are
not automatically granted to and dropped from the routine
creator.
</p>
</li>
<li class="listitem">
<p>
The creator of a routine is the account used to execute the
<code class="literal">
CREATE
</code>
statement for it. This might not be
the same as the account named as the
<code class="literal">
DEFINER
</code>
in the routine definition.
</p>
</li>
<li class="listitem">
<p>
The account named as a routine
<code class="literal">
DEFINER
</code>
can
see all routine properties, including its definition. The
account thus has full access to the routine output as produced
by:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<p>
The contents of the Information Schema
<a class="link" href="information-schema-routines-table.html" title="28.3.30 The INFORMATION_SCHEMA ROUTINES Table">
<code class="literal">
ROUTINES
</code>
</a>
table.
</p>
</li>
<li class="listitem">
<p>
The
<a class="link" href="show-create-function.html" title="15.7.7.9 SHOW CREATE FUNCTION Statement">
<code class="literal">
SHOW CREATE FUNCTION
</code>
</a>
and
<a class="link" href="show-create-procedure.html" title="15.7.7.10 SHOW CREATE PROCEDURE Statement">
<code class="literal">
SHOW CREATE PROCEDURE
</code>
</a>
statements.
</p>
</li>
<li class="listitem">
<p>
The
<a class="link" href="show-function-code.html" title="15.7.7.20 SHOW FUNCTION CODE Statement">
<code class="literal">
SHOW FUNCTION CODE
</code>
</a>
and
<a class="link" href="show-procedure-code.html" title="15.7.7.29 SHOW PROCEDURE CODE Statement">
<code class="literal">
SHOW PROCEDURE CODE
</code>
</a>
statements.
</p>
</li>
<li class="listitem">
<p>
The
<a class="link" href="show-function-status.html" title="15.7.7.21 SHOW FUNCTION STATUS Statement">
<code class="literal">
SHOW FUNCTION STATUS
</code>
</a>
and
<a class="link" href="show-procedure-status.html" title="15.7.7.30 SHOW PROCEDURE STATUS Statement">
<code class="literal">
SHOW PROCEDURE STATUS
</code>
</a>
statements.
</p>
</li>
</ul>
</div>
</li>
<li class="listitem">
<p>
For an account other than the account named as the routine
<code class="literal">
DEFINER
</code>
, access to routine properties
depends on the privileges granted to the account:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<p>
With the
<a class="link" href="privileges-provided.html#priv_show-routine">
<code class="literal">
SHOW_ROUTINE
</code>
</a>
privilege or the global
<a class="link" href="privileges-provided.html#priv_select">
<code class="literal">
SELECT
</code>
</a>
privilege, the
account can see all routine properties, including its
definition.
</p>
</li>
<li class="listitem">
<p>
With the
<a class="link" href="privileges-provided.html#priv_create-routine">
<code class="literal">
CREATE ROUTINE
</code>
</a>
,
<a class="link" href="privileges-provided.html#priv_alter-routine">
<code class="literal">
ALTER ROUTINE
</code>
</a>
or
<a class="link" href="privileges-provided.html#priv_execute">
<code class="literal">
EXECUTE
</code>
</a>
privilege granted
at a scope that includes the routine, the account can see
all routine properties except its definition.
</p>
</li>
</ul>
</div>
</li>
</ul>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/select-optimization.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="select-optimization">
</a>
10.2.1 Optimizing SELECT Statements
</h3>
</div>
</div>
</div>
<div class="toc">
<dl class="toc">
<dt>
<span class="section">
<a href="where-optimization.html">
10.2.1.1 WHERE Clause Optimization
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="range-optimization.html">
10.2.1.2 Range Optimization
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="index-merge-optimization.html">
10.2.1.3 Index Merge Optimization
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="hash-joins.html">
10.2.1.4 Hash Join Optimization
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="engine-condition-pushdown-optimization.html">
10.2.1.5 Engine Condition Pushdown Optimization
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="index-condition-pushdown-optimization.html">
10.2.1.6 Index Condition Pushdown Optimization
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="nested-loop-joins.html">
10.2.1.7 Nested-Loop Join Algorithms
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="nested-join-optimization.html">
10.2.1.8 Nested Join Optimization
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="outer-join-optimization.html">
10.2.1.9 Outer Join Optimization
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="outer-join-simplification.html">
10.2.1.10 Outer Join Simplification
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="mrr-optimization.html">
10.2.1.11 Multi-Range Read Optimization
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="bnl-bka-optimization.html">
10.2.1.12 Block Nested-Loop and Batched Key Access Joins
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="condition-filtering.html">
10.2.1.13 Condition Filtering
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="constant-folding-optimization.html">
10.2.1.14 Constant-Folding Optimization
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="is-null-optimization.html">
10.2.1.15 IS NULL Optimization
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="order-by-optimization.html">
10.2.1.16 ORDER BY Optimization
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="group-by-optimization.html">
10.2.1.17 GROUP BY Optimization
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="distinct-optimization.html">
10.2.1.18 DISTINCT Optimization
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="limit-optimization.html">
10.2.1.19 LIMIT Query Optimization
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="function-optimization.html">
10.2.1.20 Function Call Optimization
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="window-function-optimization.html">
10.2.1.21 Window Function Optimization
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="row-constructor-optimization.html">
10.2.1.22 Row Constructor Expression Optimization
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="table-scan-avoidance.html">
10.2.1.23 Avoiding Full Table Scans
</a>
</span>
</dt>
</dl>
</div>
<a class="indexterm" name="idm46045230367760">
</a>
<a class="indexterm" name="idm46045230366304">
</a>
<a class="indexterm" name="idm46045230364816">
</a>
<p>
Queries, in the form of
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT
</code>
</a>
statements, perform all the lookup operations in the database.
Tuning these statements is a top priority, whether to achieve
sub-second response times for dynamic web pages, or to chop
hours off the time to generate huge overnight reports.
</p>
<p>
Besides
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT
</code>
</a>
statements, the
tuning techniques for queries also apply to constructs such as
<a class="link" href="create-table-select.html" title="15.1.20.4 CREATE TABLE ... SELECT Statement">
<code class="literal">
CREATE
TABLE...AS SELECT
</code>
</a>
,
<a class="link" href="insert-select.html" title="15.2.7.1 INSERT ... SELECT Statement">
<code class="literal">
INSERT
INTO...SELECT
</code>
</a>
, and
<code class="literal">
WHERE
</code>
clauses in
<a class="link" href="delete.html" title="15.2.2 DELETE Statement">
<code class="literal">
DELETE
</code>
</a>
statements. Those
statements have additional performance considerations because
they combine write operations with the read-oriented query
operations.
</p>
<p>
NDB Cluster supports a join pushdown optimization whereby a
qualifying join is sent in its entirety to NDB Cluster data
nodes, where it can be distributed among them and executed in
parallel. For more information about this optimization, see
<a class="xref" href="mysql-cluster-options-variables.html#ndb_join_pushdown-conditions" title="Conditions for NDB pushdown joins">
Conditions for NDB pushdown joins
</a>
.
</p>
<p>
The main considerations for optimizing queries are:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
To make a slow
<code class="literal">
SELECT ... WHERE
</code>
query
faster, the first thing to check is whether you can add an
<a class="link" href="glossary.html#glos_index" title="index">
index
</a>
. Set up indexes on
columns used in the
<code class="literal">
WHERE
</code>
clause, to
speed up evaluation, filtering, and the final retrieval of
results. To avoid wasted disk space, construct a small set
of indexes that speed up many related queries used in your
application.
</p>
<p>
Indexes are especially important for queries that reference
different tables, using features such as
<a class="link" href="glossary.html#glos_join" title="join">
joins
</a>
and
<a class="link" href="glossary.html#glos_foreign_key" title="foreign key">
foreign keys
</a>
. You
can use the
<a class="link" href="explain.html" title="15.8.2 EXPLAIN Statement">
<code class="literal">
EXPLAIN
</code>
</a>
statement
to determine which indexes are used for a
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT
</code>
</a>
. See
<a class="xref" href="mysql-indexes.html" title="10.3.1 How MySQL Uses Indexes">
Section 10.3.1, “How MySQL Uses Indexes”
</a>
and
<a class="xref" href="using-explain.html" title="10.8.1 Optimizing Queries with EXPLAIN">
Section 10.8.1, “Optimizing Queries with EXPLAIN”
</a>
.
</p>
</li>
<li class="listitem">
<p>
Isolate and tune any part of the query, such as a function
call, that takes excessive time. Depending on how the query
is structured, a function could be called once for every row
in the result set, or even once for every row in the table,
greatly magnifying any inefficiency.
</p>
</li>
<li class="listitem">
<p>
Minimize the number of
<a class="link" href="glossary.html#glos_full_table_scan" title="full table scan">
full table scans
</a>
in your queries, particularly for big tables.
</p>
</li>
<li class="listitem">
<p>
Keep table statistics up to date by using the
<a class="link" href="analyze-table.html" title="15.7.3.1 ANALYZE TABLE Statement">
<code class="literal">
ANALYZE TABLE
</code>
</a>
statement
periodically, so the optimizer has the information needed to
construct an efficient execution plan.
</p>
</li>
<li class="listitem">
<p>
Learn the tuning techniques, indexing techniques, and
configuration parameters that are specific to the storage
engine for each table. Both
<code class="literal">
InnoDB
</code>
and
<code class="literal">
MyISAM
</code>
have sets of guidelines for
enabling and sustaining high performance in queries. For
details, see
<a class="xref" href="optimizing-innodb-queries.html" title="10.5.6 Optimizing InnoDB Queries">
Section 10.5.6, “Optimizing InnoDB Queries”
</a>
and
<a class="xref" href="optimizing-queries-myisam.html" title="10.6.1 Optimizing MyISAM Queries">
Section 10.6.1, “Optimizing MyISAM Queries”
</a>
.
</p>
</li>
<li class="listitem">
<p>
You can optimize single-query transactions for
<code class="literal">
InnoDB
</code>
tables, using the technique in
<a class="xref" href="innodb-performance-ro-txn.html" title="10.5.3 Optimizing InnoDB Read-Only Transactions">
Section 10.5.3, “Optimizing InnoDB Read-Only Transactions”
</a>
.
</p>
</li>
<li class="listitem">
<p>
Avoid transforming the query in ways that make it hard to
understand, especially if the optimizer does some of the
same transformations automatically.
</p>
</li>
<li class="listitem">
<p>
If a performance issue is not easily solved by one of the
basic guidelines, investigate the internal details of the
specific query by reading the
<a class="link" href="explain.html" title="15.8.2 EXPLAIN Statement">
<code class="literal">
EXPLAIN
</code>
</a>
plan and adjusting
your indexes,
<code class="literal">
WHERE
</code>
clauses, join
clauses, and so on. (When you reach a certain level of
expertise, reading the
<a class="link" href="explain.html" title="15.8.2 EXPLAIN Statement">
<code class="literal">
EXPLAIN
</code>
</a>
plan might be your
first step for every query.)
</p>
</li>
<li class="listitem">
<p>
Adjust the size and properties of the memory areas that
MySQL uses for caching. With efficient use of the
<code class="literal">
InnoDB
</code>
<a class="link" href="glossary.html#glos_buffer_pool" title="buffer pool">
buffer pool
</a>
,
<code class="literal">
MyISAM
</code>
key cache, and the MySQL query
cache, repeated queries run faster because the results are
retrieved from memory the second and subsequent times.
</p>
</li>
<li class="listitem">
<p>
Even for a query that runs fast using the cache memory
areas, you might still optimize further so that they require
less cache memory, making your application more scalable.
Scalability means that your application can handle more
simultaneous users, larger requests, and so on without
experiencing a big drop in performance.
</p>
</li>
<li class="listitem">
<p>
Deal with locking issues, where the speed of your query
might be affected by other sessions accessing the tables at
the same time.
</p>
</li>
</ul>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/charset-examples.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="charset-examples">
</a>
12.3.9 Examples of Character Set and Collation Assignment
</h3>
</div>
</div>
</div>
<p>
The following examples show how MySQL determines default
character set and collation values.
</p>
<p>
<span class="bold">
<strong>
Example 1: Table and Column
Definition
</strong>
</span>
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa63150703"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> t1
<span class="token punctuation">(</span>
c1 <span class="token datatype">CHAR</span><span class="token punctuation">(</span><span class="token number">10</span><span class="token punctuation">)</span> <span class="token keyword">CHARACTER</span> <span class="token keyword">SET</span> latin1 <span class="token keyword">COLLATE</span> latin1_german1_ci
<span class="token punctuation">)</span> <span class="token keyword">DEFAULT</span> <span class="token keyword">CHARACTER</span> <span class="token keyword">SET</span> latin2 <span class="token keyword">COLLATE</span> latin2_bin<span class="token punctuation">;</span></code></pre>
</div>
<p>
Here we have a column with a
<code class="literal">
latin1
</code>
character
set and a
<code class="literal">
latin1_german1_ci
</code>
collation. The
definition is explicit, so that is straightforward. Notice that
there is no problem with storing a
<code class="literal">
latin1
</code>
column in a
<code class="literal">
latin2
</code>
table.
</p>
<p>
<span class="bold">
<strong>
Example 2: Table and Column
Definition
</strong>
</span>
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa47052632"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> t1
<span class="token punctuation">(</span>
c1 <span class="token datatype">CHAR</span><span class="token punctuation">(</span><span class="token number">10</span><span class="token punctuation">)</span> <span class="token keyword">CHARACTER</span> <span class="token keyword">SET</span> latin1
<span class="token punctuation">)</span> <span class="token keyword">DEFAULT</span> <span class="token keyword">CHARACTER</span> <span class="token keyword">SET</span> latin1 <span class="token keyword">COLLATE</span> latin1_danish_ci<span class="token punctuation">;</span></code></pre>
</div>
<p>
This time we have a column with a
<code class="literal">
latin1
</code>
character set and a default collation. Although it might seem
natural, the default collation is not taken from the table
level. Instead, because the default collation for
<code class="literal">
latin1
</code>
is always
<code class="literal">
latin1_swedish_ci
</code>
, column
<code class="literal">
c1
</code>
has a collation of
<code class="literal">
latin1_swedish_ci
</code>
(not
<code class="literal">
latin1_danish_ci
</code>
).
</p>
<p>
<span class="bold">
<strong>
Example 3: Table and Column
Definition
</strong>
</span>
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa30132718"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> t1
<span class="token punctuation">(</span>
c1 <span class="token datatype">CHAR</span><span class="token punctuation">(</span><span class="token number">10</span><span class="token punctuation">)</span>
<span class="token punctuation">)</span> <span class="token keyword">DEFAULT</span> <span class="token keyword">CHARACTER</span> <span class="token keyword">SET</span> latin1 <span class="token keyword">COLLATE</span> latin1_danish_ci<span class="token punctuation">;</span></code></pre>
</div>
<p>
We have a column with a default character set and a default
collation. In this circumstance, MySQL checks the table level to
determine the column character set and collation. Consequently,
the character set for column
<code class="literal">
c1
</code>
is
<code class="literal">
latin1
</code>
and its collation is
<code class="literal">
latin1_danish_ci
</code>
.
</p>
<p>
<span class="bold">
<strong>
Example 4: Database, Table, and Column
Definition
</strong>
</span>
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa56628653"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">DATABASE</span> d1
<span class="token keyword">DEFAULT</span> <span class="token keyword">CHARACTER</span> <span class="token keyword">SET</span> latin2 <span class="token keyword">COLLATE</span> latin2_czech_cs<span class="token punctuation">;</span>
<span class="token keyword">USE</span> d1<span class="token punctuation">;</span>
<span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> t1
<span class="token punctuation">(</span>
c1 <span class="token datatype">CHAR</span><span class="token punctuation">(</span><span class="token number">10</span><span class="token punctuation">)</span>
<span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
We create a column without specifying its character set and
collation. We're also not specifying a character set and a
collation at the table level. In this circumstance, MySQL checks
the database level to determine the table settings, which
thereafter become the column settings.) Consequently, the
character set for column
<code class="literal">
c1
</code>
is
<code class="literal">
latin2
</code>
and its collation is
<code class="literal">
latin2_czech_cs
</code>
.
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/multiple-windows-command-line-servers.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="multiple-windows-command-line-servers">
</a>
7.8.2.1 Starting Multiple MySQL Instances at the Windows Command Line
</h4>
</div>
</div>
</div>
<p>
The procedure for starting a single MySQL server manually from
the command line is described in
<a class="xref" href="windows-start-command-line.html" title="2.3.3.6 Starting MySQL from the Windows Command Line">
Section 2.3.3.6, “Starting MySQL from the Windows Command Line”
</a>
. To start multiple
servers this way, you can specify the appropriate options on the
command line or in an option file. It is more convenient to
place the options in an option file, but it is necessary to make
sure that each server gets its own set of options. To do this,
create an option file for each server and tell the server the
file name with a
<a class="link" href="option-file-options.html#option_general_defaults-file">
<code class="option">
--defaults-file
</code>
</a>
option when you run it.
</p>
<p>
Suppose that you want to run one instance of
<a class="link" href="mysqld.html" title="6.3.1 mysqld — The MySQL Server">
<span class="command">
<strong>
mysqld
</strong>
</span>
</a>
on port 3307 with a data directory of
<code class="filename">
C:\mydata1
</code>
, and another instance on port
3308 with a data directory of
<code class="filename">
C:\mydata2
</code>
.
Use this procedure:
</p>
<div class="orderedlist">
<ol class="orderedlist" type="1">
<li class="listitem">
<p>
Make sure that each data directory exists, including its own
copy of the
<code class="literal">
mysql
</code>
database that contains
the grant tables.
</p>
</li>
<li class="listitem">
<p>
Create two option files. For example, create one file named
<code class="filename">
C:\my-opts1.cnf
</code>
that looks like this:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-ini"><div class="docs-select-all right" id="sa87046271"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-ini"><span class="token selector">[mysqld]</span>
<span class="token constant">datadir</span> <span class="token attr-value"><span class="token punctuation">=</span> C:/mydata1</span>
<span class="token constant">port</span> <span class="token attr-value"><span class="token punctuation">=</span> 3307</span></code></pre>
</div>
<p>
Create a second file named
<code class="filename">
C:\my-opts2.cnf
</code>
that looks like this:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-ini"><div class="docs-select-all right" id="sa37026408"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-ini"><span class="token selector">[mysqld]</span>
<span class="token constant">datadir</span> <span class="token attr-value"><span class="token punctuation">=</span> C:/mydata2</span>
<span class="token constant">port</span> <span class="token attr-value"><span class="token punctuation">=</span> 3308</span></code></pre>
</div>
</li>
<li class="listitem">
<p>
Use the
<a class="link" href="option-file-options.html#option_general_defaults-file">
<code class="option">
--defaults-file
</code>
</a>
option to start each server with its own option file:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-terminal"><div class="docs-select-all right" id="sa83222930"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-terminal"><span class="token prompt">C:\></span><span class="token command"> C:\mysql\bin\mysqld</span> <span class="token constant">--defaults-file</span><span class="token attr-value"><span class="token punctuation">=</span>C:\my-opts1.cnf</span>
<span class="token prompt">C:\></span><span class="token command"> C:\mysql\bin\mysqld</span> <span class="token constant">--defaults-file</span><span class="token attr-value"><span class="token punctuation">=</span>C:\my-opts2.cnf</span></code></pre>
</div>
<p>
Each server starts in the foreground (no new prompt appears
until the server exits later), so you need to issue those
two commands in separate console windows.
</p>
</li>
</ol>
</div>
<p>
To shut down the servers, connect to each using the appropriate
port number:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-terminal"><div class="docs-select-all right" id="sa13196989"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-terminal"><span class="token prompt">C:\></span><span class="token command"> C:\mysql\bin\mysqladmin</span> <span class="token constant">--port</span><span class="token attr-value"><span class="token punctuation">=</span>3307</span> <span class="token constant">--host</span><span class="token attr-value"><span class="token punctuation">=</span>127.0.0.1</span> <span class="token constant">--user</span><span class="token attr-value"><span class="token punctuation">=</span>root</span> <span class="token property">--password</span> shutdown
<span class="token prompt">C:\></span><span class="token command"> C:\mysql\bin\mysqladmin</span> <span class="token constant">--port</span><span class="token attr-value"><span class="token punctuation">=</span>3308</span> <span class="token constant">--host</span><span class="token attr-value"><span class="token punctuation">=</span>127.0.0.1</span> <span class="token constant">--user</span><span class="token attr-value"><span class="token punctuation">=</span>root</span> <span class="token property">--password</span> shutdown</code></pre>
</div>
<p>
Servers configured as just described permit clients to connect
over TCP/IP. If your version of Windows supports named pipes and
you also want to permit named-pipe connections, specify options
that enable the named pipe and specify its name. Each server
that supports named-pipe connections must use a unique pipe
name. For example, the
<code class="filename">
C:\my-opts1.cnf
</code>
file
might be written like this:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-ini"><div class="docs-select-all right" id="sa89201523"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-ini"><span class="token selector">[mysqld]</span>
<span class="token constant">datadir</span> <span class="token attr-value"><span class="token punctuation">=</span> C:/mydata1</span>
<span class="token constant">port</span> <span class="token attr-value"><span class="token punctuation">=</span> 3307</span>
<span class="token constant">enable-named-pipe</span>
<span class="token constant">socket</span> <span class="token attr-value"><span class="token punctuation">=</span> mypipe1</span></code></pre>
</div>
<p>
Modify
<code class="filename">
C:\my-opts2.cnf
</code>
similarly for use by
the second server. Then start the servers as described
previously.
</p>
<p>
A similar procedure applies for servers that you want to permit
shared-memory connections. Enable such connections by starting
the server with the
<a class="link" href="server-system-variables.html#sysvar_shared_memory">
<code class="literal">
shared_memory
</code>
</a>
system variable
enabled and specify a unique shared-memory name for each server
by setting the
<a class="link" href="server-system-variables.html#sysvar_shared_memory_base_name">
<code class="literal">
shared_memory_base_name
</code>
</a>
system
variable.
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/drop-table.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="drop-table">
</a>
15.1.32 DROP TABLE Statement
</h3>
</div>
</div>
</div>
<a class="indexterm" name="idm46045183342992">
</a>
<a class="indexterm" name="idm46045183341920">
</a>
<a class="indexterm" name="idm46045183340432">
</a>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa8635500"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">DROP</span> <span class="token punctuation">[</span><span class="token keyword">TEMPORARY</span><span class="token punctuation">]</span> <span class="token keyword">TABLE</span> <span class="token punctuation">[</span><span class="token keyword">IF</span> <span class="token keyword">EXISTS</span><span class="token punctuation">]</span>
<em class="replaceable">tbl_name</em> <span class="token punctuation">[</span><span class="token punctuation">,</span> <em class="replaceable">tbl_name</em><span class="token punctuation">]</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token punctuation">[</span><span class="token keyword">RESTRICT</span> <span class="token operator">|</span> <span class="token keyword">CASCADE</span><span class="token punctuation">]</span></code></pre>
</div>
<p>
<a class="link" href="drop-table.html" title="15.1.32 DROP TABLE Statement">
<code class="literal">
DROP TABLE
</code>
</a>
removes one or more
tables. You must have the
<a class="link" href="privileges-provided.html#priv_drop">
<code class="literal">
DROP
</code>
</a>
privilege for each table.
</p>
<p>
<span class="emphasis">
<em>
Be careful
</em>
</span>
with this statement! For each
table, it removes the table definition and all table data. If the
table is partitioned, the statement removes the table definition,
all its partitions, all data stored in those partitions, and all
partition definitions associated with the dropped table.
</p>
<p>
Dropping a table also drops any triggers for the table.
</p>
<p>
<a class="link" href="drop-table.html" title="15.1.32 DROP TABLE Statement">
<code class="literal">
DROP TABLE
</code>
</a>
causes an implicit
commit, except when used with the
<code class="literal">
TEMPORARY
</code>
keyword. See
<a class="xref" href="implicit-commit.html" title="15.3.3 Statements That Cause an Implicit Commit">
Section 15.3.3, “Statements That Cause an Implicit Commit”
</a>
.
</p>
<div class="important" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Important
</div>
<p>
When a table is dropped, privileges granted specifically for the
table are
<span class="emphasis">
<em>
not
</em>
</span>
automatically dropped. They
must be dropped manually. See
<a class="xref" href="grant.html" title="15.7.1.6 GRANT Statement">
Section 15.7.1.6, “GRANT Statement”
</a>
.
</p>
</div>
<p>
If any tables named in the argument list do not exist,
<a class="link" href="drop-table.html" title="15.1.32 DROP TABLE Statement">
<code class="literal">
DROP TABLE
</code>
</a>
behavior depends on
whether the
<code class="literal">
IF EXISTS
</code>
clause is given:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
Without
<code class="literal">
IF EXISTS
</code>
, the statement fails with
an error indicating which nonexisting tables it was unable to
drop, and no changes are made.
</p>
</li>
<li class="listitem">
<p>
With
<code class="literal">
IF EXISTS
</code>
, no error occurs for
nonexisting tables. The statement drops all named tables that
do exist, and generates a
<code class="literal">
NOTE
</code>
diagnostic
for each nonexistent table. These notes can be displayed with
<a class="link" href="show-warnings.html" title="15.7.7.42 SHOW WARNINGS Statement">
<code class="literal">
SHOW WARNINGS
</code>
</a>
. See
<a class="xref" href="show-warnings.html" title="15.7.7.42 SHOW WARNINGS Statement">
Section 15.7.7.42, “SHOW WARNINGS Statement”
</a>
.
</p>
</li>
</ul>
</div>
<p>
<code class="literal">
IF EXISTS
</code>
can also be useful for dropping
tables in unusual circumstances under which there is an entry in
the data dictionary but no table managed by the storage engine.
(For example, if an abnormal server exit occurs after removal of
the table from the storage engine but before removal of the data
dictionary entry.)
</p>
<p>
The
<code class="literal">
TEMPORARY
</code>
keyword has the following
effects:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
The statement drops only
<code class="literal">
TEMPORARY
</code>
tables.
</p>
</li>
<li class="listitem">
<p>
The statement does not cause an implicit commit.
</p>
</li>
<li class="listitem">
<p>
No access rights are checked. A
<code class="literal">
TEMPORARY
</code>
table is visible only with the session that created it, so no
check is necessary.
</p>
</li>
</ul>
</div>
<p>
Including the
<code class="literal">
TEMPORARY
</code>
keyword is a good way
to prevent accidentally dropping non-
<code class="literal">
TEMPORARY
</code>
tables.
</p>
<p>
The
<code class="literal">
RESTRICT
</code>
and
<code class="literal">
CASCADE
</code>
keywords do nothing. They are permitted to make porting easier
from other database systems.
</p>
<p>
<a class="link" href="drop-table.html" title="15.1.32 DROP TABLE Statement">
<code class="literal">
DROP TABLE
</code>
</a>
is not supported with
all
<a class="link" href="innodb-parameters.html#sysvar_innodb_force_recovery">
<code class="literal">
innodb_force_recovery
</code>
</a>
settings. See
<a class="xref" href="forcing-innodb-recovery.html" title="17.20.3 Forcing InnoDB Recovery">
Section 17.20.3, “Forcing InnoDB Recovery”
</a>
.
</p>
<a class="indexterm" name="idm46045183301680">
</a>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/information-schema-routines-table.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="information-schema-routines-table">
</a>
28.3.30 The INFORMATION_SCHEMA ROUTINES Table
</h3>
</div>
</div>
</div>
<a class="indexterm" name="idm46045078892720">
</a>
<p>
The
<a class="link" href="information-schema-routines-table.html" title="28.3.30 The INFORMATION_SCHEMA ROUTINES Table">
<code class="literal">
ROUTINES
</code>
</a>
table provides
information about stored routines (stored procedures and stored
functions). The
<a class="link" href="information-schema-routines-table.html" title="28.3.30 The INFORMATION_SCHEMA ROUTINES Table">
<code class="literal">
ROUTINES
</code>
</a>
table does
not include built-in (native) functions or loadable functions.
</p>
<p>
The
<a class="link" href="information-schema-routines-table.html" title="28.3.30 The INFORMATION_SCHEMA ROUTINES Table">
<code class="literal">
ROUTINES
</code>
</a>
table has these columns:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<code class="literal">
SPECIFIC_NAME
</code>
</p>
<p>
The name of the routine.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
ROUTINE_CATALOG
</code>
</p>
<p>
The name of the catalog to which the routine belongs. This
value is always
<code class="literal">
def
</code>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
ROUTINE_SCHEMA
</code>
</p>
<p>
The name of the schema (database) to which the routine
belongs.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
ROUTINE_NAME
</code>
</p>
<p>
The name of the routine.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
ROUTINE_TYPE
</code>
</p>
<p>
<code class="literal">
PROCEDURE
</code>
for stored procedures,
<code class="literal">
FUNCTION
</code>
for stored functions.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
DATA_TYPE
</code>
</p>
<p>
If the routine is a stored function, the return value data
type. If the routine is a stored procedure, this value is
empty.
</p>
<p>
The
<code class="literal">
DATA_TYPE
</code>
value is the type name only
with no other information. The
<code class="literal">
DTD_IDENTIFIER
</code>
value contains the type name
and possibly other information such as the precision or
length.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
CHARACTER_MAXIMUM_LENGTH
</code>
</p>
<p>
For stored function string return values, the maximum length
in characters. If the routine is a stored procedure, this
value is
<code class="literal">
NULL
</code>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
CHARACTER_OCTET_LENGTH
</code>
</p>
<p>
For stored function string return values, the maximum length
in bytes. If the routine is a stored procedure, this value is
<code class="literal">
NULL
</code>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
NUMERIC_PRECISION
</code>
</p>
<p>
For stored function numeric return values, the numeric
precision. If the routine is a stored procedure, this value is
<code class="literal">
NULL
</code>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
NUMERIC_SCALE
</code>
</p>
<p>
For stored function numeric return values, the numeric scale.
If the routine is a stored procedure, this value is
<code class="literal">
NULL
</code>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
DATETIME_PRECISION
</code>
</p>
<p>
For stored function temporal return values, the fractional
seconds precision. If the routine is a stored procedure, this
value is
<code class="literal">
NULL
</code>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
CHARACTER_SET_NAME
</code>
</p>
<p>
For stored function character string return values, the
character set name. If the routine is a stored procedure, this
value is
<code class="literal">
NULL
</code>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
COLLATION_NAME
</code>
</p>
<p>
For stored function character string return values, the
collation name. If the routine is a stored procedure, this
value is
<code class="literal">
NULL
</code>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
DTD_IDENTIFIER
</code>
</p>
<p>
If the routine is a stored function, the return value data
type. If the routine is a stored procedure, this value is
empty.
</p>
<p>
The
<code class="literal">
DATA_TYPE
</code>
value is the type name only
with no other information. The
<code class="literal">
DTD_IDENTIFIER
</code>
value contains the type name
and possibly other information such as the precision or
length.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
ROUTINE_BODY
</code>
</p>
<p>
The language used for the routine definition. This value is
always
<code class="literal">
SQL
</code>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
ROUTINE_DEFINITION
</code>
</p>
<p>
The text of the SQL statement executed by the routine.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
EXTERNAL_NAME
</code>
</p>
<p>
This value is always
<code class="literal">
NULL
</code>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
EXTERNAL_LANGUAGE
</code>
</p>
<p>
The language of the stored routine. The value is read from the
<code class="literal">
external_language
</code>
column of the
<code class="literal">
mysql.routines
</code>
data dictionary table.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
PARAMETER_STYLE
</code>
</p>
<p>
This value is always
<code class="literal">
SQL
</code>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
IS_DETERMINISTIC
</code>
</p>
<p>
<code class="literal">
YES
</code>
or
<code class="literal">
NO
</code>
, depending on
whether the routine is defined with the
<code class="literal">
DETERMINISTIC
</code>
characteristic.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
SQL_DATA_ACCESS
</code>
</p>
<p>
The data access characteristic for the routine. The value is
one of
<code class="literal">
CONTAINS SQL
</code>
,
<code class="literal">
NO
SQL
</code>
,
<code class="literal">
READS SQL DATA
</code>
, or
<code class="literal">
MODIFIES SQL DATA
</code>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
SQL_PATH
</code>
</p>
<p>
This value is always
<code class="literal">
NULL
</code>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
SECURITY_TYPE
</code>
</p>
<p>
The routine
<code class="literal">
SQL SECURITY
</code>
characteristic.
The value is one of
<code class="literal">
DEFINER
</code>
or
<code class="literal">
INVOKER
</code>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
CREATED
</code>
</p>
<p>
The date and time when the routine was created. This is a
<a class="link" href="datetime.html" title="13.2.2 The DATE, DATETIME, and TIMESTAMP Types">
<code class="literal">
TIMESTAMP
</code>
</a>
value.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
LAST_ALTERED
</code>
</p>
<p>
The date and time when the routine was last modified. This is
a
<a class="link" href="datetime.html" title="13.2.2 The DATE, DATETIME, and TIMESTAMP Types">
<code class="literal">
TIMESTAMP
</code>
</a>
value. If the
routine has not been modified since its creation, this value
is the same as the
<code class="literal">
CREATED
</code>
value.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
SQL_MODE
</code>
</p>
<p>
The SQL mode in effect when the routine was created or
altered, and under which the routine executes. For the
permitted values, see
<a class="xref" href="sql-mode.html" title="7.1.11 Server SQL Modes">
Section 7.1.11, “Server SQL Modes”
</a>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
ROUTINE_COMMENT
</code>
</p>
<p>
The text of the comment, if the routine has one. If not, this
value is empty.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
DEFINER
</code>
</p>
<p>
The account named in the
<code class="literal">
DEFINER
</code>
clause
(often the user who created the routine), in
<code class="literal">
'
<em class="replaceable">
<code>
user_name
</code>
</em>
'@'
<em class="replaceable">
<code>
host_name
</code>
</em>
'
</code>
format.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
CHARACTER_SET_CLIENT
</code>
</p>
<p>
The session value of the
<a class="link" href="server-system-variables.html#sysvar_character_set_client">
<code class="literal">
character_set_client
</code>
</a>
system
variable when the routine was created.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
COLLATION_CONNECTION
</code>
</p>
<p>
The session value of the
<a class="link" href="server-system-variables.html#sysvar_collation_connection">
<code class="literal">
collation_connection
</code>
</a>
system
variable when the routine was created.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
DATABASE_COLLATION
</code>
</p>
<p>
The collation of the database with which the routine is
associated.
</p>
</li>
</ul>
</div>
<h4>
<a name="idm46045078794016">
</a>
Notes
</h4>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
To see information about a routine, you must be the user named
as the routine
<code class="literal">
DEFINER
</code>
, have the
<a class="link" href="privileges-provided.html#priv_show-routine">
<code class="literal">
SHOW_ROUTINE
</code>
</a>
privilege, have
the
<a class="link" href="privileges-provided.html#priv_select">
<code class="literal">
SELECT
</code>
</a>
privilege at the
global level, or have the
<a class="link" href="privileges-provided.html#priv_create-routine">
<code class="literal">
CREATE
ROUTINE
</code>
</a>
,
<a class="link" href="privileges-provided.html#priv_alter-routine">
<code class="literal">
ALTER
ROUTINE
</code>
</a>
, or
<a class="link" href="privileges-provided.html#priv_execute">
<code class="literal">
EXECUTE
</code>
</a>
privilege granted at a scope that includes the routine. The
<code class="literal">
ROUTINE_DEFINITION
</code>
column is
<code class="literal">
NULL
</code>
if you have only
<a class="link" href="privileges-provided.html#priv_create-routine">
<code class="literal">
CREATE ROUTINE
</code>
</a>
,
<a class="link" href="privileges-provided.html#priv_alter-routine">
<code class="literal">
ALTER ROUTINE
</code>
</a>
, or
<a class="link" href="privileges-provided.html#priv_execute">
<code class="literal">
EXECUTE
</code>
</a>
.
</p>
</li>
<li class="listitem">
<p>
Information about stored function return values is also
available in the
<a class="link" href="information-schema-parameters-table.html" title="28.3.20 The INFORMATION_SCHEMA PARAMETERS Table">
<code class="literal">
PARAMETERS
</code>
</a>
table. The return value row for a stored function can be
identified as the row that has an
<code class="literal">
ORDINAL_POSITION
</code>
value of 0.
</p>
</li>
</ul>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/optimizing-spatial-analysis.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="optimizing-spatial-analysis">
</a>
13.4.9 Optimizing Spatial Analysis
</h3>
</div>
</div>
</div>
<p>
For
<a class="link" href="myisam-storage-engine.html" title="18.2 The MyISAM Storage Engine">
<code class="literal">
MyISAM
</code>
</a>
and
<code class="literal">
InnoDB
</code>
tables, search operations in columns
containing spatial data can be optimized using
<code class="literal">
SPATIAL
</code>
indexes. The most typical operations
are:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
Point queries that search for all objects that contain a
given point
</p>
</li>
<li class="listitem">
<p>
Region queries that search for all objects that overlap a
given region
</p>
</li>
</ul>
</div>
<p>
MySQL uses
<span class="bold">
<strong>
R-Trees with quadratic
splitting
</strong>
</span>
for
<code class="literal">
SPATIAL
</code>
indexes on
spatial columns. A
<code class="literal">
SPATIAL
</code>
index is built
using the minimum bounding rectangle (MBR) of a geometry. For
most geometries, the MBR is a minimum rectangle that surrounds
the geometries. For a horizontal or a vertical linestring, the
MBR is a rectangle degenerated into the linestring. For a point,
the MBR is a rectangle degenerated into the point.
</p>
<p>
It is also possible to create normal indexes on spatial columns.
In a non-
<code class="literal">
SPATIAL
</code>
index, you must declare a
prefix for any spatial column except for
<code class="literal">
POINT
</code>
columns.
</p>
<p>
<code class="literal">
MyISAM
</code>
and
<code class="literal">
InnoDB
</code>
support
both
<code class="literal">
SPATIAL
</code>
and
non-
<code class="literal">
SPATIAL
</code>
indexes. Other storage engines
support non-
<code class="literal">
SPATIAL
</code>
indexes, as described in
<a class="xref" href="create-index.html" title="15.1.15 CREATE INDEX Statement">
Section 15.1.15, “CREATE INDEX Statement”
</a>
.
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/exists-and-not-exists-subqueries.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="exists-and-not-exists-subqueries">
</a>
15.2.15.6 Subqueries with EXISTS or NOT EXISTS
</h4>
</div>
</div>
</div>
<a class="indexterm" name="idm46045179883472">
</a>
<a class="indexterm" name="idm46045179881984">
</a>
<a class="indexterm" name="idm46045179880496">
</a>
<a class="indexterm" name="idm46045179879008">
</a>
<p>
If a subquery returns any rows at all,
<code class="literal">
EXISTS
<em class="replaceable">
<code>
subquery
</code>
</em>
</code>
is
<code class="literal">
TRUE
</code>
, and
<code class="literal">
NOT EXISTS
<em class="replaceable">
<code>
subquery
</code>
</em>
</code>
is
<code class="literal">
FALSE
</code>
. For example:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa88291049"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">SELECT</span> column1 <span class="token keyword">FROM</span> t1 <span class="token keyword">WHERE</span> <span class="token keyword">EXISTS</span> <span class="token punctuation">(</span><span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> t2<span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
Traditionally, an
<code class="literal">
EXISTS
</code>
subquery starts with
<code class="literal">
SELECT *
</code>
, but it could begin with
<code class="literal">
SELECT 5
</code>
or
<code class="literal">
SELECT column1
</code>
or anything at all. MySQL ignores the
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT
</code>
</a>
list in such a subquery,
so it makes no difference.
</p>
<p>
For the preceding example, if
<code class="literal">
t2
</code>
contains any
rows, even rows with nothing but
<code class="literal">
NULL
</code>
values,
the
<code class="literal">
EXISTS
</code>
condition is
<code class="literal">
TRUE
</code>
. This is actually an unlikely example
because a
<code class="literal">
[NOT] EXISTS
</code>
subquery almost always
contains correlations. Here are some more realistic examples:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
What kind of store is present in one or more cities?
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa904344"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">SELECT</span> <span class="token keyword">DISTINCT</span> store_type <span class="token keyword">FROM</span> stores
<span class="token keyword">WHERE</span> <span class="token keyword">EXISTS</span> <span class="token punctuation">(</span><span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> cities_stores
<span class="token keyword">WHERE</span> cities_stores<span class="token punctuation">.</span>store_type <span class="token operator">=</span> stores<span class="token punctuation">.</span>store_type<span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
</li>
<li class="listitem">
<p>
What kind of store is present in no cities?
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa56714266"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">SELECT</span> <span class="token keyword">DISTINCT</span> store_type <span class="token keyword">FROM</span> stores
<span class="token keyword">WHERE</span> <span class="token operator">NOT</span> <span class="token keyword">EXISTS</span> <span class="token punctuation">(</span><span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> cities_stores
<span class="token keyword">WHERE</span> cities_stores<span class="token punctuation">.</span>store_type <span class="token operator">=</span> stores<span class="token punctuation">.</span>store_type<span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
</li>
<li class="listitem">
<p>
What kind of store is present in all cities?
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa27076457"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">SELECT</span> <span class="token keyword">DISTINCT</span> store_type <span class="token keyword">FROM</span> stores
<span class="token keyword">WHERE</span> <span class="token operator">NOT</span> <span class="token keyword">EXISTS</span> <span class="token punctuation">(</span>
<span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> cities <span class="token keyword">WHERE</span> <span class="token operator">NOT</span> <span class="token keyword">EXISTS</span> <span class="token punctuation">(</span>
<span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> cities_stores
<span class="token keyword">WHERE</span> cities_stores<span class="token punctuation">.</span>city <span class="token operator">=</span> cities<span class="token punctuation">.</span>city
<span class="token operator">AND</span> cities_stores<span class="token punctuation">.</span>store_type <span class="token operator">=</span> stores<span class="token punctuation">.</span>store_type<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
</li>
</ul>
</div>
<p>
The last example is a double-nested
<code class="literal">
NOT
EXISTS
</code>
query. That is, it has a
<code class="literal">
NOT
EXISTS
</code>
clause within a
<code class="literal">
NOT EXISTS
</code>
clause. Formally, it answers the question
<span class="quote">
“
<span class="quote">
does a city
exist with a store that is not in
<code class="literal">
Stores
</code>
</span>
”
</span>
? But it is easier to say that
a nested
<code class="literal">
NOT EXISTS
</code>
answers the question
<span class="quote">
“
<span class="quote">
is
<em class="replaceable">
<code>
x
</code>
</em>
<code class="literal">
TRUE
</code>
for all
<em class="replaceable">
<code>
y
</code>
</em>
?
</span>
”
</span>
</p>
<p>
You can also use
<code class="literal">
NOT EXISTS
</code>
or
<code class="literal">
NOT
EXISTS
</code>
with
<a class="link" href="table.html" title="15.2.16 TABLE Statement">
<code class="literal">
TABLE
</code>
</a>
in
the subquery, like this:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa36384172"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">SELECT</span> column1 <span class="token keyword">FROM</span> t1 <span class="token keyword">WHERE</span> <span class="token keyword">EXISTS</span> <span class="token punctuation">(</span><span class="token keyword">TABLE</span> t2<span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
The results are the same as when using
<code class="literal">
SELECT
*
</code>
with no
<code class="literal">
WHERE
</code>
clause in the
subquery.
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/xa.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="xa">
</a>
15.3.8 XA Transactions
</h3>
</div>
</div>
</div>
<div class="toc">
<dl class="toc">
<dt>
<span class="section">
<a href="xa-statements.html">
15.3.8.1 XA Transaction SQL Statements
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="xa-states.html">
15.3.8.2 XA Transaction States
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="xa-restrictions.html">
15.3.8.3 Restrictions on XA Transactions
</a>
</span>
</dt>
</dl>
</div>
<a class="indexterm" name="idm46045178138944">
</a>
<p>
Support for
<a class="link" href="glossary.html#glos_xa" title="XA">
XA
</a>
transactions is
available for the
<a class="link" href="innodb-storage-engine.html" title="Chapter 17 The InnoDB Storage Engine">
<code class="literal">
InnoDB
</code>
</a>
storage
engine. The MySQL XA implementation is based on the X/Open CAE
document
<em class="citetitle">
Distributed Transaction Processing: The XA
Specification
</em>
. This document is published by The Open
Group and available at
<a class="ulink" href="http://www.opengroup.org/public/pubs/catalog/c193.htm" target="_blank">
http://www.opengroup.org/public/pubs/catalog/c193.htm
</a>
.
Limitations of the current XA implementation are described in
<a class="xref" href="xa-restrictions.html" title="15.3.8.3 Restrictions on XA Transactions">
Section 15.3.8.3, “Restrictions on XA Transactions”
</a>
.
</p>
<p>
On the client side, there are no special requirements. The XA
interface to a MySQL server consists of SQL statements that begin
with the
<code class="literal">
XA
</code>
keyword. MySQL client programs must
be able to send SQL statements and to understand the semantics of
the XA statement interface. They do not need be linked against a
recent client library. Older client libraries also work.
</p>
<p>
Among the MySQL Connectors, MySQL Connector/J 5.0.0 and higher
supports XA directly, by means of a class interface that handles
the XA SQL statement interface for you.
</p>
<p>
XA supports distributed transactions, that is, the ability to
permit multiple separate transactional resources to participate in
a global transaction. Transactional resources often are RDBMSs but
may be other kinds of resources.
</p>
<p>
A global transaction involves several actions that are
transactional in themselves, but that all must either complete
successfully as a group, or all be rolled back as a group. In
essence, this extends ACID properties
<span class="quote">
“
<span class="quote">
up a level
</span>
”
</span>
so
that multiple ACID transactions can be executed in concert as
components of a global operation that also has ACID properties.
(As with nondistributed transactions,
<a class="link" href="innodb-transaction-isolation-levels.html#isolevel_serializable">
<code class="literal">
SERIALIZABLE
</code>
</a>
may be preferred
if your applications are sensitive to read phenomena.
<a class="link" href="innodb-transaction-isolation-levels.html#isolevel_repeatable-read">
<code class="literal">
REPEATABLE READ
</code>
</a>
may not be
sufficient for distributed transactions.)
</p>
<p>
Some examples of distributed transactions:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
An application may act as an integration tool that combines a
messaging service with an RDBMS. The application makes sure
that transactions dealing with message sending, retrieval, and
processing that also involve a transactional database all
happen in a global transaction. You can think of this as
<span class="quote">
“
<span class="quote">
transactional email.
</span>
”
</span>
</p>
</li>
<li class="listitem">
<p>
An application performs actions that involve different
database servers, such as a MySQL server and an Oracle server
(or multiple MySQL servers), where actions that involve
multiple servers must happen as part of a global transaction,
rather than as separate transactions local to each server.
</p>
</li>
<li class="listitem">
<p>
A bank keeps account information in an RDBMS and distributes
and receives money through automated teller machines (ATMs).
It is necessary to ensure that ATM actions are correctly
reflected in the accounts, but this cannot be done with the
RDBMS alone. A global transaction manager integrates the ATM
and database resources to ensure overall consistency of
financial transactions.
</p>
</li>
</ul>
</div>
<p>
Applications that use global transactions involve one or more
Resource Managers and a Transaction Manager:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
A Resource Manager (RM) provides access to transactional
resources. A database server is one kind of resource manager.
It must be possible to either commit or roll back transactions
managed by the RM.
</p>
</li>
<li class="listitem">
<p>
A Transaction Manager (TM) coordinates the transactions that
are part of a global transaction. It communicates with the RMs
that handle each of these transactions. The individual
transactions within a global transaction are
<span class="quote">
“
<span class="quote">
branches
</span>
”
</span>
of the global transaction. Global
transactions and their branches are identified by a naming
scheme described later.
</p>
</li>
</ul>
</div>
<p>
The MySQL implementation of XA enables a MySQL server to act as a
Resource Manager that handles XA transactions within a global
transaction. A client program that connects to the MySQL server
acts as the Transaction Manager.
</p>
<p>
To carry out a global transaction, it is necessary to know which
components are involved, and bring each component to a point when
it can be committed or rolled back. Depending on what each
component reports about its ability to succeed, they must all
commit or roll back as an atomic group. That is, either all
components must commit, or all components must roll back. To
manage a global transaction, it is necessary to take into account
that any component or the connecting network might fail.
</p>
<p>
The process for executing a global transaction uses two-phase
commit (2PC). This takes place after the actions performed by the
branches of the global transaction have been executed.
</p>
<div class="orderedlist">
<ol class="orderedlist" type="1">
<li class="listitem">
<p>
In the first phase, all branches are prepared. That is, they
are told by the TM to get ready to commit. Typically, this
means each RM that manages a branch records the actions for
the branch in stable storage. The branches indicate whether
they are able to do this, and these results are used for the
second phase.
</p>
</li>
<li class="listitem">
<p>
In the second phase, the TM tells the RMs whether to commit or
roll back. If all branches indicated when they were prepared
that they were able to commit, all branches are told to
commit. If any branch indicated when it was prepared that it
was not able to commit, all branches are told to roll back.
</p>
</li>
</ol>
</div>
<p>
In some cases, a global transaction might use one-phase commit
(1PC). For example, when a Transaction Manager finds that a global
transaction consists of only one transactional resource (that is,
a single branch), that resource can be told to prepare and commit
at the same time.
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/innodb-monitor-types.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="innodb-monitor-types">
</a>
17.17.1 InnoDB Monitor Types
</h3>
</div>
</div>
</div>
<a class="indexterm" name="idm46045149438016">
</a>
<a class="indexterm" name="idm46045149436944">
</a>
<p>
There are two types of
<code class="literal">
InnoDB
</code>
monitor:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
The standard
<code class="literal">
InnoDB
</code>
Monitor displays the
following types of information:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<p>
Work done by the main background thread
</p>
</li>
<li class="listitem">
<p>
Semaphore waits
</p>
</li>
<li class="listitem">
<p>
Data about the most recent foreign key and deadlock errors
</p>
</li>
<li class="listitem">
<p>
Lock waits for transactions
</p>
</li>
<li class="listitem">
<p>
Table and record locks held by active transactions
</p>
</li>
<li class="listitem">
<p>
Pending I/O operations and related statistics
</p>
</li>
<li class="listitem">
<p>
Insert buffer and adaptive hash index statistics
</p>
</li>
<li class="listitem">
<p>
Redo log data
</p>
</li>
<li class="listitem">
<p>
Buffer pool statistics
</p>
</li>
<li class="listitem">
<p>
Row operation data
</p>
</li>
</ul>
</div>
</li>
<li class="listitem">
<p>
The
<code class="literal">
InnoDB
</code>
Lock Monitor prints additional
lock information as part of the standard
<code class="literal">
InnoDB
</code>
Monitor output.
</p>
</li>
</ul>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/replication-features-functions.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="replication-features-functions">
</a>
19.5.1.14 Replication and System Functions
</h4>
</div>
</div>
</div>
<a class="indexterm" name="idm46045135598816">
</a>
<a class="indexterm" name="idm46045135597328">
</a>
<p>
Certain functions do not replicate well under some conditions:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
The
<a class="link" href="information-functions.html#function_user">
<code class="literal">
USER()
</code>
</a>
,
<a class="link" href="information-functions.html#function_current-user">
<code class="literal">
CURRENT_USER()
</code>
</a>
(or
<a class="link" href="information-functions.html#function_current-user">
<code class="literal">
CURRENT_USER
</code>
</a>
),
<a class="link" href="miscellaneous-functions.html#function_uuid">
<code class="literal">
UUID()
</code>
</a>
,
<a class="link" href="information-functions.html#function_version">
<code class="literal">
VERSION()
</code>
</a>
, and
<a class="link" href="string-functions.html#function_load-file">
<code class="literal">
LOAD_FILE()
</code>
</a>
functions are
replicated without change and thus do not work reliably on
the replica unless row-based replication is enabled. (See
<a class="xref" href="replication-formats.html" title="19.2.1 Replication Formats">
Section 19.2.1, “Replication Formats”
</a>
.)
</p>
<p>
<a class="link" href="information-functions.html#function_user">
<code class="literal">
USER()
</code>
</a>
and
<a class="link" href="information-functions.html#function_current-user">
<code class="literal">
CURRENT_USER()
</code>
</a>
are
automatically replicated using row-based replication when
using
<code class="literal">
MIXED
</code>
mode, and generate a warning
in
<code class="literal">
STATEMENT
</code>
mode. (See also
<a class="xref" href="replication-features-current-user.html" title="19.5.1.8 Replication of CURRENT_USER()">
Section 19.5.1.8, “Replication of CURRENT_USER()”
</a>
.) This
is also true for
<a class="link" href="information-functions.html#function_version">
<code class="literal">
VERSION()
</code>
</a>
and
<a class="link" href="mathematical-functions.html#function_rand">
<code class="literal">
RAND()
</code>
</a>
.
</p>
</li>
<li class="listitem">
<p>
For
<a class="link" href="date-and-time-functions.html#function_now">
<code class="literal">
NOW()
</code>
</a>
, the binary log
includes the timestamp. This means that the value
<span class="emphasis">
<em>
as returned by the call to this function on the
source
</em>
</span>
is replicated to the replica. To avoid
unexpected results when replicating between MySQL servers in
different time zones, set the time zone on both source and
replica. For more information, see
<a class="xref" href="replication-features-timezone.html" title="19.5.1.33 Replication and Time Zones">
Section 19.5.1.33, “Replication and Time Zones”
</a>
.
</p>
<p>
To explain the potential problems when replicating between
servers which are in different time zones, suppose that the
source is located in New York, the replica is located in
Stockholm, and both servers are using local time. Suppose
further that, on the source, you create a table
<code class="literal">
mytable
</code>
, perform an
<a class="link" href="insert.html" title="15.2.7 INSERT Statement">
<code class="literal">
INSERT
</code>
</a>
statement on this
table, and then select from the table, as shown here:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa78360471"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> mytable <span class="token punctuation">(</span>mycol <span class="token datatype">TEXT</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token output">Query OK, 0 rows affected (0.06 sec)</span>
<span class="token prompt">mysql></span> <span class="token keyword">INSERT</span> <span class="token keyword">INTO</span> mytable <span class="token keyword">VALUES</span> <span class="token punctuation">(</span> <span class="token function">NOW</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token output">Query OK, 1 row affected (0.00 sec)</span>
<span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> mytable<span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> mycol <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> 2009<span class="token punctuation">-</span>09<span class="token punctuation">-</span>01 12:00:00 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output">1 row in set (0.00 sec)</span></code></pre>
</div>
<p>
Local time in Stockholm is 6 hours later than in New York;
so, if you issue
<code class="literal">
SELECT NOW()
</code>
on the
replica at that exact same instant, the value
<code class="literal">
2009-09-01 18:00:00
</code>
is returned. For this
reason, if you select from the replica's copy of
<code class="literal">
mytable
</code>
after the
<a class="link" href="create-table.html" title="15.1.20 CREATE TABLE Statement">
<code class="literal">
CREATE TABLE
</code>
</a>
and
<a class="link" href="insert.html" title="15.2.7 INSERT Statement">
<code class="literal">
INSERT
</code>
</a>
statements just shown
have been replicated, you might expect
<code class="literal">
mycol
</code>
to contain the value
<code class="literal">
2009-09-01 18:00:00
</code>
. However, this is not
the case; when you select from the replica's copy of
<code class="literal">
mytable
</code>
, you obtain exactly the same
result as on the source:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa97323813"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> mytable<span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> mycol <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> 2009<span class="token punctuation">-</span>09<span class="token punctuation">-</span>01 12:00:00 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output">1 row in set (0.00 sec)</span></code></pre>
</div>
<p>
Unlike
<a class="link" href="date-and-time-functions.html#function_now">
<code class="literal">
NOW()
</code>
</a>
, the
<a class="link" href="date-and-time-functions.html#function_sysdate">
<code class="literal">
SYSDATE()
</code>
</a>
function is not
replication-safe because it is not affected by
<code class="literal">
SET
TIMESTAMP
</code>
statements in the binary log and is
nondeterministic if statement-based logging is used. This is
not a problem if row-based logging is used.
</p>
<p>
An alternative is to use the
<a class="link" href="server-options.html#option_mysqld_sysdate-is-now">
<code class="option">
--sysdate-is-now
</code>
</a>
option to
cause
<a class="link" href="date-and-time-functions.html#function_sysdate">
<code class="literal">
SYSDATE()
</code>
</a>
to be an
alias for
<a class="link" href="date-and-time-functions.html#function_now">
<code class="literal">
NOW()
</code>
</a>
. This must be
done on the source and the replica to work correctly. In
such cases, a warning is still issued by this function, but
can safely be ignored as long as
<a class="link" href="server-options.html#option_mysqld_sysdate-is-now">
<code class="option">
--sysdate-is-now
</code>
</a>
is used on
both the source and the replica.
</p>
<p>
<a class="link" href="date-and-time-functions.html#function_sysdate">
<code class="literal">
SYSDATE()
</code>
</a>
is automatically
replicated using row-based replication when using
<code class="literal">
MIXED
</code>
mode, and generates a warning in
<code class="literal">
STATEMENT
</code>
mode.
</p>
<p>
See also
<a class="xref" href="replication-features-timezone.html" title="19.5.1.33 Replication and Time Zones">
Section 19.5.1.33, “Replication and Time Zones”
</a>
.
</p>
</li>
<li class="listitem">
<p>
<span class="emphasis">
<em>
The following restriction applies to
statement-based replication only, not to row-based
replication.
</em>
</span>
The
<a class="link" href="locking-functions.html#function_get-lock">
<code class="literal">
GET_LOCK()
</code>
</a>
,
<a class="link" href="locking-functions.html#function_release-lock">
<code class="literal">
RELEASE_LOCK()
</code>
</a>
,
<a class="link" href="locking-functions.html#function_is-free-lock">
<code class="literal">
IS_FREE_LOCK()
</code>
</a>
, and
<a class="link" href="locking-functions.html#function_is-used-lock">
<code class="literal">
IS_USED_LOCK()
</code>
</a>
functions that
handle user-level locks are replicated without the replica
knowing the concurrency context on the source. Therefore,
these functions should not be used to insert into a source
table because the content on the replica would differ. For
example, do not issue a statement such as
<code class="literal">
INSERT
INTO mytable VALUES(GET_LOCK(...))
</code>
.
</p>
<p>
These functions are automatically replicated using row-based
replication when using
<code class="literal">
MIXED
</code>
mode, and
generate a warning in
<code class="literal">
STATEMENT
</code>
mode.
</p>
</li>
</ul>
</div>
<p>
As a workaround for the preceding limitations when
statement-based replication is in effect, you can use the
strategy of saving the problematic function result in a user
variable and referring to the variable in a later statement. For
example, the following single-row
<a class="link" href="insert.html" title="15.2.7 INSERT Statement">
<code class="literal">
INSERT
</code>
</a>
is problematic due to the
reference to the
<a class="link" href="miscellaneous-functions.html#function_uuid">
<code class="literal">
UUID()
</code>
</a>
function:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa17752089"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">INSERT</span> <span class="token keyword">INTO</span> t <span class="token keyword">VALUES</span><span class="token punctuation">(</span><span class="token function">UUID</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
To work around the problem, do this instead:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa56771735"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">SET</span> <span class="token variable">@my_uuid</span> <span class="token operator">=</span> <span class="token function">UUID</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">INSERT</span> <span class="token keyword">INTO</span> t <span class="token keyword">VALUES</span><span class="token punctuation">(</span><span class="token variable">@my_uuid</span><span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
That sequence of statements replicates because the value of
<code class="literal">
@my_uuid
</code>
is stored in the binary log as a
user-variable event prior to the
<a class="link" href="insert.html" title="15.2.7 INSERT Statement">
<code class="literal">
INSERT
</code>
</a>
statement and is available
for use in the
<a class="link" href="insert.html" title="15.2.7 INSERT Statement">
<code class="literal">
INSERT
</code>
</a>
.
</p>
<p>
The same idea applies to multiple-row inserts, but is more
cumbersome to use. For a two-row insert, you can do this:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa12982007"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">SET</span> <span class="token variable">@my_uuid1</span> <span class="token operator">=</span> <span class="token function">UUID</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token variable">@my_uuid2</span> <span class="token operator">=</span> <span class="token function">UUID</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">INSERT</span> <span class="token keyword">INTO</span> t <span class="token keyword">VALUES</span><span class="token punctuation">(</span><span class="token variable">@my_uuid1</span><span class="token punctuation">)</span><span class="token punctuation">,</span><span class="token punctuation">(</span><span class="token variable">@my_uuid2</span><span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
However, if the number of rows is large or unknown, the
workaround is difficult or impracticable. For example, you
cannot convert the following statement to one in which a given
individual user variable is associated with each row:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa17787917"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">INSERT</span> <span class="token keyword">INTO</span> t2 <span class="token keyword">SELECT</span> <span class="token function">UUID</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> t1<span class="token punctuation">;</span></code></pre>
</div>
<p>
Within a stored function,
<a class="link" href="mathematical-functions.html#function_rand">
<code class="literal">
RAND()
</code>
</a>
replicates correctly as long as it is invoked only once during
the execution of the function. (You can consider the function
execution timestamp and random number seed as implicit inputs
that are identical on the source and replica.)
</p>
<p>
The
<a class="link" href="information-functions.html#function_found-rows">
<code class="literal">
FOUND_ROWS()
</code>
</a>
and
<a class="link" href="information-functions.html#function_row-count">
<code class="literal">
ROW_COUNT()
</code>
</a>
functions are not
replicated reliably using statement-based replication. A
workaround is to store the result of the function call in a user
variable, and then use that in the
<a class="link" href="insert.html" title="15.2.7 INSERT Statement">
<code class="literal">
INSERT
</code>
</a>
statement. For example, if
you wish to store the result in a table named
<code class="literal">
mytable
</code>
, you might normally do so like this:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa3393329"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">SELECT</span> <span class="token keyword">SQL_CALC_FOUND_ROWS</span> <span class="token keyword">FROM</span> mytable <span class="token keyword">LIMIT</span> <span class="token number">1</span><span class="token punctuation">;</span>
<span class="token keyword">INSERT</span> <span class="token keyword">INTO</span> mytable <span class="token keyword">VALUES</span><span class="token punctuation">(</span> <span class="token function">FOUND_ROWS</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
However, if you are replicating
<code class="literal">
mytable
</code>
, you
should use
<a class="link" href="select-into.html" title="15.2.13.1 SELECT ... INTO Statement">
<code class="literal">
SELECT
... INTO
</code>
</a>
, and then store the variable in the table,
like this:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa45264141"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">SELECT</span> <span class="token keyword">SQL_CALC_FOUND_ROWS</span> <span class="token keyword">INTO</span> <span class="token variable">@found_rows</span> <span class="token keyword">FROM</span> mytable <span class="token keyword">LIMIT</span> <span class="token number">1</span><span class="token punctuation">;</span>
<span class="token keyword">INSERT</span> <span class="token keyword">INTO</span> mytable <span class="token keyword">VALUES</span><span class="token punctuation">(</span><span class="token variable">@found_rows</span><span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
In this way, the user variable is replicated as part of the
context, and applied on the replica correctly.
</p>
<p>
These functions are automatically replicated using row-based
replication when using
<code class="literal">
MIXED
</code>
mode, and
generate a warning in
<code class="literal">
STATEMENT
</code>
mode. (Bug
#12092, Bug #30244)
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/optimizing-innodb-logging.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="optimizing-innodb-logging">
</a>
10.5.4 Optimizing InnoDB Redo Logging
</h3>
</div>
</div>
</div>
<p>
Consider the following guidelines for optimizing redo logging:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
Increase the size of your redo log files. When
<code class="literal">
InnoDB
</code>
has written redo log files full,
it must write the modified contents of the buffer pool to
disk in a
<a class="link" href="glossary.html#glos_checkpoint" title="checkpoint">
checkpoint
</a>
.
Small redo log files cause many unnecessary disk writes.
</p>
<p>
The redo log file size is determined by
<a class="link" href="innodb-parameters.html#sysvar_innodb_redo_log_capacity">
<code class="literal">
innodb_redo_log_capacity
</code>
</a>
.
<code class="literal">
InnoDB
</code>
tries to maintain 32 redo log
files of the same size, with each file equal to 1/32 *
<code class="literal">
innodb_redo_log_capacity
</code>
. Therefore,
changing the
<code class="literal">
innodb_redo_log_capacity
</code>
setting changes the size of the redo log files.
</p>
<p>
For information about modifying your redo log file
configuration, see
<a class="xref" href="innodb-redo-log.html" title="17.6.5 Redo Log">
Section 17.6.5, “Redo Log”
</a>
.
</p>
</li>
<li class="listitem">
<p>
Consider increasing the size of the
<a class="link" href="glossary.html#glos_log_buffer" title="log buffer">
log buffer
</a>
. A large
log buffer enables large
<a class="link" href="glossary.html#glos_transaction" title="transaction">
transactions
</a>
to run
without a need to write the log to disk before the
transactions
<a class="link" href="glossary.html#glos_commit" title="commit">
commit
</a>
.
Thus, if you have transactions that update, insert, or
delete many rows, making the log buffer larger saves disk
I/O. Log buffer size is configured using the
<a class="link" href="innodb-parameters.html#sysvar_innodb_log_buffer_size">
<code class="literal">
innodb_log_buffer_size
</code>
</a>
configuration option, which can be dynamically configured.
</p>
</li>
<li class="listitem">
<p>
Configure the
<a class="link" href="innodb-parameters.html#sysvar_innodb_log_write_ahead_size">
<code class="literal">
innodb_log_write_ahead_size
</code>
</a>
configuration option to avoid
<span class="quote">
“
<span class="quote">
read-on-write
</span>
”
</span>
.
This option defines the write-ahead block size for the redo
log. Set
<a class="link" href="innodb-parameters.html#sysvar_innodb_log_write_ahead_size">
<code class="literal">
innodb_log_write_ahead_size
</code>
</a>
to match the operating system or file system cache block
size. Read-on-write occurs when redo log blocks are not
entirely cached to the operating system or file system due
to a mismatch between write-ahead block size for the redo
log and operating system or file system cache block size.
</p>
<p>
Valid values for
<a class="link" href="innodb-parameters.html#sysvar_innodb_log_write_ahead_size">
<code class="literal">
innodb_log_write_ahead_size
</code>
</a>
are multiples of the
<code class="literal">
InnoDB
</code>
log file
block size (2
<sup>
n
</sup>
). The minimum
value is the
<code class="literal">
InnoDB
</code>
log file block size
(512). Write-ahead does not occur when the minimum value is
specified. The maximum value is equal to the
<a class="link" href="innodb-parameters.html#sysvar_innodb_page_size">
<code class="literal">
innodb_page_size
</code>
</a>
value. If
you specify a value for
<a class="link" href="innodb-parameters.html#sysvar_innodb_log_write_ahead_size">
<code class="literal">
innodb_log_write_ahead_size
</code>
</a>
that is larger than the
<a class="link" href="innodb-parameters.html#sysvar_innodb_page_size">
<code class="literal">
innodb_page_size
</code>
</a>
value, the
<a class="link" href="innodb-parameters.html#sysvar_innodb_log_write_ahead_size">
<code class="literal">
innodb_log_write_ahead_size
</code>
</a>
setting is truncated to the
<a class="link" href="innodb-parameters.html#sysvar_innodb_page_size">
<code class="literal">
innodb_page_size
</code>
</a>
value.
</p>
<p>
Setting the
<a class="link" href="innodb-parameters.html#sysvar_innodb_log_write_ahead_size">
<code class="literal">
innodb_log_write_ahead_size
</code>
</a>
value too low in relation to the operating system or file
system cache block size results in read-on-write. Setting
the value too high may have a slight impact on
<code class="literal">
fsync
</code>
performance for log file writes due
to several blocks being written at once.
</p>
</li>
<li class="listitem">
<p>
MySQL provides dedicated log writer threads for writing redo
log records from the log buffer to the system buffers and
flushing the system buffers to the redo log files. You can
enable or disable log writer threads using the
<a class="link" href="innodb-parameters.html#sysvar_innodb_log_writer_threads">
<code class="literal">
innodb_log_writer_threads
</code>
</a>
variable. Dedicated log writer threads can improve
performance on high-concurrency systems, but for
low-concurrency systems, disabling dedicated log writer
threads provides better performance.
</p>
</li>
<li class="listitem">
<p>
Optimize the use of spin delay by user threads waiting for
flushed redo. Spin delay helps reduce latency. During
periods of low concurrency, reducing latency may be less of
a priority, and avoiding the use of spin delay during these
periods may reduce energy consumption. During periods of
high concurrency, you may want to avoid expending processing
power on spin delay so that it can be used for other work.
The following system variables permit setting high and low
watermark values that define boundaries for the use of spin
delay.
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<p>
<a class="link" href="innodb-parameters.html#sysvar_innodb_log_wait_for_flush_spin_hwm">
<code class="literal">
innodb_log_wait_for_flush_spin_hwm
</code>
</a>
:
Defines the maximum average log flush time beyond which
user threads no longer spin while waiting for flushed
redo. The default value is 400 microseconds.
</p>
</li>
<li class="listitem">
<p>
<a class="link" href="innodb-parameters.html#sysvar_innodb_log_spin_cpu_abs_lwm">
<code class="literal">
innodb_log_spin_cpu_abs_lwm
</code>
</a>
:
Defines the minimum amount of CPU usage below which user
threads no longer spin while waiting for flushed redo.
The value is expressed as a sum of CPU core usage. For
example, The default value of 80 is 80% of a single CPU
core. On a system with a multi-core processor, a value
of 150 represents 100% usage of one CPU core plus 50%
usage of a second CPU core.
</p>
</li>
<li class="listitem">
<p>
<a class="link" href="innodb-parameters.html#sysvar_innodb_log_spin_cpu_pct_hwm">
<code class="literal">
innodb_log_spin_cpu_pct_hwm
</code>
</a>
:
Defines the maximum amount of CPU usage above which user
threads no longer spin while waiting for flushed redo.
The value is expressed as a percentage of the combined
total processing power of all CPU cores. The default
value is 50%. For example, 100% usage of two CPU cores
is 50% of the combined CPU processing power on a server
with four CPU cores.
</p>
<p>
The
<a class="link" href="innodb-parameters.html#sysvar_innodb_log_spin_cpu_pct_hwm">
<code class="literal">
innodb_log_spin_cpu_pct_hwm
</code>
</a>
configuration option respects processor affinity. For
example, if a server has 48 cores but the
<a class="link" href="mysqld.html" title="6.3.1 mysqld — The MySQL Server">
<span class="command">
<strong>
mysqld
</strong>
</span>
</a>
process is pinned to only four
CPU cores, the other 44 CPU cores are ignored.
</p>
</li>
</ul>
</div>
</li>
</ul>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/gis-format-conversion-functions.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="gis-format-conversion-functions">
</a>
14.16.6 Geometry Format Conversion Functions
</h3>
</div>
</div>
</div>
<p>
MySQL supports the functions listed in this section for converting
geometry values from internal geometry format to WKT or WKB
format, or for swapping the order of X and Y coordinates.
</p>
<p>
There are also functions to convert a string from WKT or WKB
format to internal geometry format. See
<a class="xref" href="gis-wkt-functions.html" title="14.16.3 Functions That Create Geometry Values from WKT Values">
Section 14.16.3, “Functions That Create Geometry Values from WKT Values”
</a>
, and
<a class="xref" href="gis-wkb-functions.html" title="14.16.4 Functions That Create Geometry Values from WKB Values">
Section 14.16.4, “Functions That Create Geometry Values from WKB Values”
</a>
.
</p>
<p>
Functions such as
<a class="link" href="gis-wkt-functions.html#function_st-geomfromtext">
<code class="literal">
ST_GeomFromText()
</code>
</a>
that accept WKT geometry collection arguments understand both
OpenGIS
<code class="literal">
'GEOMETRYCOLLECTION EMPTY'
</code>
standard
syntax and MySQL
<code class="literal">
'GEOMETRYCOLLECTION()'
</code>
nonstandard syntax. Another way to produce an empty geometry
collection is by calling
<a class="link" href="gis-mysql-specific-functions.html#function_geometrycollection">
<code class="literal">
GeometryCollection()
</code>
</a>
with no
arguments. Functions such as
<a class="link" href="gis-format-conversion-functions.html#function_st-astext">
<code class="literal">
ST_AsWKT()
</code>
</a>
that produce WKT values produce
<code class="literal">
'GEOMETRYCOLLECTION
EMPTY'
</code>
standard syntax:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa88517658"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SET</span> <span class="token variable">@s1</span> <span class="token operator">=</span> <span class="token function">ST_GeomFromText</span><span class="token punctuation">(</span><span class="token string">'GEOMETRYCOLLECTION()'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token prompt">mysql></span> <span class="token keyword">SET</span> <span class="token variable">@s2</span> <span class="token operator">=</span> <span class="token function">ST_GeomFromText</span><span class="token punctuation">(</span><span class="token string">'GEOMETRYCOLLECTION EMPTY'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token function">ST_AsWKT</span><span class="token punctuation">(</span><span class="token variable">@s1</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token function">ST_AsWKT</span><span class="token punctuation">(</span><span class="token variable">@s2</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> ST_AsWKT(@s1) <span class="token punctuation">|</span> ST_AsWKT(@s2) <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> GEOMETRYCOLLECTION EMPTY <span class="token punctuation">|</span> GEOMETRYCOLLECTION EMPTY <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token function">ST_AsWKT</span><span class="token punctuation">(</span><span class="token function">GeomCollection</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> ST_AsWKT(GeomCollection()) <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> GEOMETRYCOLLECTION EMPTY <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span></code></pre>
</div>
<p>
Unless otherwise specified, functions in this section handle their
geometry arguments as follows:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
If any argument is
<code class="literal">
NULL
</code>
, the return value
is
<code class="literal">
NULL
</code>
.
</p>
</li>
<li class="listitem">
<p>
If any geometry argument is not a syntactically well-formed
geometry, an
<a class="ulink" href="/doc/mysql-errors/8.4/en/server-error-reference.html#error_er_gis_invalid_data" target="_top">
<code class="literal">
ER_GIS_INVALID_DATA
</code>
</a>
error
occurs.
</p>
</li>
<li class="listitem">
<p>
If any geometry argument is in an undefined spatial reference
system, the axes are output in the order they appear in the
geometry and an
<a class="ulink" href="/doc/mysql-errors/8.4/en/server-error-reference.html#error_er_warn_srs_not_found_axis_order" target="_top">
<code class="literal">
ER_WARN_SRS_NOT_FOUND_AXIS_ORDER
</code>
</a>
warning occurs.
</p>
</li>
<li class="listitem">
<p>
By default, geographic coordinates (latitude, longitude) are
interpreted as in the order specified by the spatial reference
system of geometry arguments. An optional
<em class="replaceable">
<code>
options
</code>
</em>
argument may be given to
override the default axis order.
<code class="option">
options
</code>
consists of a list of comma-separated
<code class="literal">
<em class="replaceable">
<code>
key
</code>
</em>
=
<em class="replaceable">
<code>
value
</code>
</em>
</code>
.
The only permitted
<em class="replaceable">
<code>
key
</code>
</em>
value is
<code class="literal">
axis-order
</code>
, with permitted values of
<code class="literal">
lat-long
</code>
,
<code class="literal">
long-lat
</code>
and
<code class="literal">
srid-defined
</code>
(the default).
</p>
<p>
If the
<em class="replaceable">
<code>
options
</code>
</em>
argument is
<code class="literal">
NULL
</code>
, the return value is
<code class="literal">
NULL
</code>
. If the
<em class="replaceable">
<code>
options
</code>
</em>
argument is invalid, an
error occurs to indicate why.
</p>
</li>
<li class="listitem">
<p>
Otherwise, the return value is non-
<code class="literal">
NULL
</code>
.
</p>
</li>
</ul>
</div>
<p>
These functions are available for format conversions or coordinate
swapping:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<a name="function_st-asbinary">
</a>
<p>
<a class="link" href="gis-format-conversion-functions.html#function_st-asbinary">
<code class="literal">
ST_AsBinary(
<em class="replaceable">
<code>
g
</code>
</em>
[,
<em class="replaceable">
<code>
options
</code>
</em>
])
</code>
</a>
,
<a class="link" href="gis-format-conversion-functions.html#function_st-asbinary">
<code class="literal">
ST_AsWKB(
<em class="replaceable">
<code>
g
</code>
</em>
[,
<em class="replaceable">
<code>
options
</code>
</em>
])
</code>
</a>
</p>
<a class="indexterm" name="idm46045197620176">
</a>
<p>
Converts a value in internal geometry format to its WKB
representation and returns the binary result.
</p>
<p>
The function return value has geographic coordinates
(latitude, longitude) in the order specified by the spatial
reference system that applies to the geometry argument. An
optional
<em class="replaceable">
<code>
options
</code>
</em>
argument may be
given to override the default axis order.
</p>
<p>
<a class="link" href="gis-format-conversion-functions.html#function_st-asbinary">
<code class="literal">
ST_AsBinary()
</code>
</a>
and
<a class="link" href="gis-format-conversion-functions.html#function_st-asbinary">
<code class="literal">
ST_AsWKB()
</code>
</a>
handle their arguments as described in the introduction to
this section.
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa165295"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SET</span> <span class="token variable">@g</span> <span class="token operator">=</span> <span class="token function">ST_LineFromText</span><span class="token punctuation">(</span><span class="token string">'LINESTRING(0 5,5 10,10 15)'</span><span class="token punctuation">,</span> <span class="token number">4326</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token function">ST_AsText</span><span class="token punctuation">(</span><span class="token function">ST_GeomFromWKB</span><span class="token punctuation">(</span><span class="token function">ST_AsWKB</span><span class="token punctuation">(</span><span class="token variable">@g</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> ST_AsText(ST_GeomFromWKB(ST_AsWKB(@g))) <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> LINESTRING(5 0,10 5,15 10) <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token function">ST_AsText</span><span class="token punctuation">(</span><span class="token function">ST_GeomFromWKB</span><span class="token punctuation">(</span><span class="token function">ST_AsWKB</span><span class="token punctuation">(</span><span class="token variable">@g</span><span class="token punctuation">,</span> <span class="token string">'axis-order=long-lat'</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> ST_AsText(ST_GeomFromWKB(ST_AsWKB(@g, 'axis<span class="token punctuation">-</span>order=long<span class="token punctuation">-</span>lat'))) <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> LINESTRING(0 5,5 10,10 15) <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token function">ST_AsText</span><span class="token punctuation">(</span><span class="token function">ST_GeomFromWKB</span><span class="token punctuation">(</span><span class="token function">ST_AsWKB</span><span class="token punctuation">(</span><span class="token variable">@g</span><span class="token punctuation">,</span> <span class="token string">'axis-order=lat-long'</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> ST_AsText(ST_GeomFromWKB(ST_AsWKB(@g, 'axis<span class="token punctuation">-</span>order=lat<span class="token punctuation">-</span>long'))) <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> LINESTRING(5 0,10 5,15 10) <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span></code></pre>
</div>
</li>
<li class="listitem">
<a name="function_st-astext">
</a>
<p>
<a class="link" href="gis-format-conversion-functions.html#function_st-astext">
<code class="literal">
ST_AsText(
<em class="replaceable">
<code>
g
</code>
</em>
[,
<em class="replaceable">
<code>
options
</code>
</em>
])
</code>
</a>
,
<a class="link" href="gis-format-conversion-functions.html#function_st-astext">
<code class="literal">
ST_AsWKT(
<em class="replaceable">
<code>
g
</code>
</em>
[,
<em class="replaceable">
<code>
options
</code>
</em>
])
</code>
</a>
</p>
<a class="indexterm" name="idm46045197600720">
</a>
<p>
Converts a value in internal geometry format to its WKT
representation and returns the string result.
</p>
<p>
The function return value has geographic coordinates
(latitude, longitude) in the order specified by the spatial
reference system that applies to the geometry argument. An
optional
<em class="replaceable">
<code>
options
</code>
</em>
argument may be
given to override the default axis order.
</p>
<p>
<a class="link" href="gis-format-conversion-functions.html#function_st-astext">
<code class="literal">
ST_AsText()
</code>
</a>
and
<a class="link" href="gis-format-conversion-functions.html#function_st-astext">
<code class="literal">
ST_AsWKT()
</code>
</a>
handle their arguments as described in the introduction to
this section.
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa39076025"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SET</span> <span class="token variable">@g</span> <span class="token operator">=</span> <span class="token string">'LineString(1 1,2 2,3 3)'</span><span class="token punctuation">;</span>
<span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token function">ST_AsText</span><span class="token punctuation">(</span><span class="token function">ST_GeomFromText</span><span class="token punctuation">(</span><span class="token variable">@g</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> ST_AsText(ST_GeomFromText(@g)) <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> LINESTRING(1 1,2 2,3 3) <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span></code></pre>
</div>
<p>
Output for
<code class="literal">
MultiPoint
</code>
values includes
parentheses around each point. For example:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa37002269"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token function">ST_AsText</span><span class="token punctuation">(</span><span class="token function">ST_GeomFromText</span><span class="token punctuation">(</span><span class="token variable">@mp</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> ST_AsText(ST_GeomFromText(@mp)) <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> MULTIPOINT((1 1),(2 2),(3 3)) <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span></code></pre>
</div>
</li>
<li class="listitem">
<a name="function_st-swapxy">
</a>
<p>
<a class="link" href="gis-format-conversion-functions.html#function_st-swapxy">
<code class="literal">
ST_SwapXY(
<em class="replaceable">
<code>
g
</code>
</em>
)
</code>
</a>
</p>
<a class="indexterm" name="idm46045197583600">
</a>
<p>
Accepts an argument in internal geometry format, swaps the X
and Y values of each coordinate pair within the geometry, and
returns the result.
</p>
<p>
<a class="link" href="gis-format-conversion-functions.html#function_st-swapxy">
<code class="literal">
ST_SwapXY()
</code>
</a>
handles its
arguments as described in the introduction to this section.
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa95022736"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SET</span> <span class="token variable">@g</span> <span class="token operator">=</span> <span class="token function">ST_LineFromText</span><span class="token punctuation">(</span><span class="token string">'LINESTRING(0 5,5 10,10 15)'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token function">ST_AsText</span><span class="token punctuation">(</span><span class="token variable">@g</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> ST_AsText(@g) <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> LINESTRING(0 5,5 10,10 15) <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token function">ST_AsText</span><span class="token punctuation">(</span><span class="token function">ST_SwapXY</span><span class="token punctuation">(</span><span class="token variable">@g</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> ST_AsText(ST_SwapXY(@g)) <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> LINESTRING(5 0,10 5,15 10) <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span></code></pre>
</div>
</li>
</ul>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/information-schema-innodb-ft-deleted-table.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="information-schema-innodb-ft-deleted-table">
</a>
28.4.17 The INFORMATION_SCHEMA INNODB_FT_DELETED Table
</h3>
</div>
</div>
</div>
<a class="indexterm" name="idm46045076852832">
</a>
<p>
The
<a class="link" href="information-schema-innodb-ft-deleted-table.html" title="28.4.17 The INFORMATION_SCHEMA INNODB_FT_DELETED Table">
<code class="literal">
INNODB_FT_DELETED
</code>
</a>
table stores
rows that are deleted from the
<code class="literal">
FULLTEXT
</code>
index
for an
<code class="literal">
InnoDB
</code>
table. To avoid expensive index
reorganization during DML operations for an
<code class="literal">
InnoDB
</code>
<code class="literal">
FULLTEXT
</code>
index, the
information about newly deleted words is stored separately,
filtered out of search results when you do a text search, and
removed from the main search index only when you issue an
<a class="link" href="optimize-table.html" title="15.7.3.4 OPTIMIZE TABLE Statement">
<code class="literal">
OPTIMIZE TABLE
</code>
</a>
statement for the
<code class="literal">
InnoDB
</code>
table. For more information, see
<a class="xref" href="fulltext-fine-tuning.html#fulltext-optimize" title="Optimizing InnoDB Full-Text Indexes">
Optimizing InnoDB Full-Text Indexes
</a>
.
</p>
<p>
This table is empty initially. Before querying it, set the value
of the
<a class="link" href="innodb-parameters.html#sysvar_innodb_ft_aux_table">
<code class="literal">
innodb_ft_aux_table
</code>
</a>
system
variable to the name (including the database name) of the table
that contains the
<code class="literal">
FULLTEXT
</code>
index (for example,
<code class="literal">
test/articles
</code>
).
</p>
<p>
For related usage information and examples, see
<a class="xref" href="innodb-information-schema-fulltext_index-tables.html" title="17.15.4 InnoDB INFORMATION_SCHEMA FULLTEXT Index Tables">
Section 17.15.4, “InnoDB INFORMATION_SCHEMA FULLTEXT Index Tables”
</a>
.
</p>
<p>
The
<a class="link" href="information-schema-innodb-ft-deleted-table.html" title="28.4.17 The INFORMATION_SCHEMA INNODB_FT_DELETED Table">
<code class="literal">
INNODB_FT_DELETED
</code>
</a>
table has these
columns:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<code class="literal">
DOC_ID
</code>
</p>
<p>
The document ID of the newly deleted row. This value might
reflect the value of an ID column that you defined for the
underlying table, or it can be a sequence value generated by
<code class="literal">
InnoDB
</code>
when the table contains no suitable
column. This value is used when you perform text searches, to
skip rows in the
<a class="link" href="information-schema-innodb-ft-index-table-table.html" title="28.4.19 The INFORMATION_SCHEMA INNODB_FT_INDEX_TABLE Table">
<code class="literal">
INNODB_FT_INDEX_TABLE
</code>
</a>
table
before data for deleted rows is physically removed from the
<code class="literal">
FULLTEXT
</code>
index by an
<a class="link" href="optimize-table.html" title="15.7.3.4 OPTIMIZE TABLE Statement">
<code class="literal">
OPTIMIZE TABLE
</code>
</a>
statement. For
more information, see
<a class="xref" href="fulltext-fine-tuning.html#fulltext-optimize" title="Optimizing InnoDB Full-Text Indexes">
Optimizing InnoDB Full-Text Indexes
</a>
.
</p>
</li>
</ul>
</div>
<h4>
<a name="idm46045076830240">
</a>
Example
</h4>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa1218571"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> INFORMATION_SCHEMA<span class="token punctuation">.</span>INNODB_FT_DELETED<span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> DOC_ID <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> 6 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> 7 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> 8 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span></code></pre>
</div>
<h4>
<a name="idm46045076827808">
</a>
Notes
</h4>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
You must have the
<a class="link" href="privileges-provided.html#priv_process">
<code class="literal">
PROCESS
</code>
</a>
privilege to query this table.
</p>
</li>
<li class="listitem">
<p>
Use the
<code class="literal">
INFORMATION_SCHEMA
</code>
<a class="link" href="information-schema-columns-table.html" title="28.3.8 The INFORMATION_SCHEMA COLUMNS Table">
<code class="literal">
COLUMNS
</code>
</a>
table or the
<a class="link" href="show-columns.html" title="15.7.7.6 SHOW COLUMNS Statement">
<code class="literal">
SHOW COLUMNS
</code>
</a>
statement to view
additional information about the columns of this table,
including data types and default values.
</p>
</li>
<li class="listitem">
<p>
For more information about
<code class="literal">
InnoDB
</code>
<code class="literal">
FULLTEXT
</code>
search, see
<a class="xref" href="innodb-fulltext-index.html" title="17.6.2.4 InnoDB Full-Text Indexes">
Section 17.6.2.4, “InnoDB Full-Text Indexes”
</a>
, and
<a class="xref" href="fulltext-search.html" title="14.9 Full-Text Search Functions">
Section 14.9, “Full-Text Search Functions”
</a>
.
</p>
</li>
</ul>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/mysql-cluster-ndbinfo-table-info.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="mysql-cluster-ndbinfo-table-info">
</a>
25.6.17.59 The ndbinfo table_info Table
</h4>
</div>
</div>
</div>
<a class="indexterm" name="idm46045087694832">
</a>
<p>
The
<code class="literal">
table_info
</code>
table provides information
about logging, checkpointing, distribution, and storage options
in effect for individual
<code class="literal">
NDB
</code>
tables.
</p>
<p>
The
<code class="literal">
table_info
</code>
table contains the following
columns:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<code class="literal">
table_id
</code>
</p>
<p>
Table ID
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
logged_table
</code>
</p>
<p>
Whether table is logged (1) or not (0)
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
row_contains_gci
</code>
</p>
<p>
Whether table rows contain GCI (1 true, 0 false)
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
row_contains_checksum
</code>
</p>
<p>
Whether table rows contain checksum (1 true, 0 false)
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
read_backup
</code>
</p>
<p>
If backup fragment replicas are read this is 1, otherwise 0
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
fully_replicated
</code>
</p>
<p>
If table is fully replicated this is 1, otherwise 0
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
storage_type
</code>
</p>
<p>
Table storage type; one of
<code class="literal">
MEMORY
</code>
or
<code class="literal">
DISK
</code>
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
hashmap_id
</code>
</p>
<p>
Hashmap ID
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
partition_balance
</code>
</p>
<p>
Partition balance (fragment count type) used for table; one
of
<code class="literal">
FOR_RP_BY_NODE
</code>
,
<code class="literal">
FOR_RA_BY_NODE
</code>
,
<code class="literal">
FOR_RP_BY_LDM
</code>
, or
<code class="literal">
FOR_RA_BY_LDM
</code>
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
create_gci
</code>
</p>
<p>
GCI in which table was created
</p>
</li>
</ul>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/searching-on-two-keys.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="searching-on-two-keys">
</a>
5.6.7 Searching on Two Keys
</h3>
</div>
</div>
</div>
<a class="indexterm" name="idm46045324624288">
</a>
<a class="indexterm" name="idm46045324623248">
</a>
<a class="indexterm" name="idm46045324622176">
</a>
<a class="indexterm" name="idm46045324620688">
</a>
<p>
An
<a class="link" href="logical-operators.html#operator_or">
<code class="literal">
OR
</code>
</a>
using a single key is well
optimized, as is the handling of
<a class="link" href="logical-operators.html#operator_and">
<code class="literal">
AND
</code>
</a>
.
</p>
<p>
The one tricky case is that of searching on two different keys
combined with
<a class="link" href="logical-operators.html#operator_or">
<code class="literal">
OR
</code>
</a>
:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa52073969"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">SELECT</span> field1_index<span class="token punctuation">,</span> field2_index <span class="token keyword">FROM</span> test_table
<span class="token keyword">WHERE</span> field1_index <span class="token operator">=</span> <span class="token string">'1'</span> <span class="token operator">OR</span> field2_index <span class="token operator">=</span> <span class="token string">'1'</span></code></pre>
</div>
<p>
This case is optimized. See
<a class="xref" href="index-merge-optimization.html" title="10.2.1.3 Index Merge Optimization">
Section 10.2.1.3, “Index Merge Optimization”
</a>
.
</p>
<p>
You can also solve the problem efficiently by using a
<a class="link" href="union.html" title="15.2.18 UNION Clause">
<code class="literal">
UNION
</code>
</a>
that combines the output of
two separate
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT
</code>
</a>
statements.
See
<a class="xref" href="union.html" title="15.2.18 UNION Clause">
Section 15.2.18, “UNION Clause”
</a>
.
</p>
<p>
Each
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT
</code>
</a>
searches only one key
and can be optimized:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa65784381"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">SELECT</span> field1_index<span class="token punctuation">,</span> field2_index
<span class="token keyword">FROM</span> test_table <span class="token keyword">WHERE</span> field1_index <span class="token operator">=</span> <span class="token string">'1'</span>
<span class="token keyword">UNION</span>
<span class="token keyword">SELECT</span> field1_index<span class="token punctuation">,</span> field2_index
<span class="token keyword">FROM</span> test_table <span class="token keyword">WHERE</span> field2_index <span class="token operator">=</span> <span class="token string">'1'</span><span class="token punctuation">;</span></code></pre>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/precision-math-examples.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="precision-math-examples">
</a>
14.24.5 Precision Math Examples
</h3>
</div>
</div>
</div>
<p>
This section provides some examples that show precision math query
results in MySQL. These examples demonstrate the principles
described in
<a class="xref" href="precision-math-expressions.html" title="14.24.3 Expression Handling">
Section 14.24.3, “Expression Handling”
</a>
, and
<a class="xref" href="precision-math-rounding.html" title="14.24.4 Rounding Behavior">
Section 14.24.4, “Rounding Behavior”
</a>
.
</p>
<p>
<span class="bold">
<strong>
Example 1
</strong>
</span>
. Numbers are used with
their exact value as given when possible:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa9574596"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token punctuation">(</span><span class="token punctuation">.</span><span class="token number">1</span> <span class="token operator">+</span> <span class="token punctuation">.</span><span class="token number">2</span><span class="token punctuation">)</span> <span class="token operator">=</span> <span class="token punctuation">.</span><span class="token number">3</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> (.1 <span class="token punctuation">+</span> .2) = .3 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> 1 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span></code></pre>
</div>
<p>
For floating-point values, results are inexact:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa60355171"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token punctuation">(</span><span class="token punctuation">.</span><span class="token number">1E0</span> <span class="token operator">+</span> <span class="token punctuation">.</span><span class="token number">2E0</span><span class="token punctuation">)</span> <span class="token operator">=</span> <span class="token punctuation">.</span><span class="token number">3E0</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> (.1E0 <span class="token punctuation">+</span> .2E0) = .3E0 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> 0 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span></code></pre>
</div>
<p>
Another way to see the difference in exact and approximate value
handling is to add a small number to a sum many times. Consider
the following stored procedure, which adds
<code class="literal">
.0001
</code>
to a variable 1,000 times.
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa60565819"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">PROCEDURE</span> p <span class="token punctuation">(</span><span class="token punctuation">)</span>
<span class="token keyword">BEGIN</span>
<span class="token keyword">DECLARE</span> i <span class="token datatype">INT</span> <span class="token keyword">DEFAULT</span> <span class="token number">0</span><span class="token punctuation">;</span>
<span class="token keyword">DECLARE</span> d <span class="token datatype">DECIMAL</span><span class="token punctuation">(</span><span class="token number">10</span><span class="token punctuation">,</span><span class="token number">4</span><span class="token punctuation">)</span> <span class="token keyword">DEFAULT</span> <span class="token number">0</span><span class="token punctuation">;</span>
<span class="token keyword">DECLARE</span> f <span class="token datatype">FLOAT</span> <span class="token keyword">DEFAULT</span> <span class="token number">0</span><span class="token punctuation">;</span>
<span class="token keyword">WHILE</span> i <span class="token operator"><</span> <span class="token number">10000</span> <span class="token keyword">DO</span>
<span class="token keyword">SET</span> d <span class="token operator">=</span> d <span class="token operator">+</span> <span class="token punctuation">.</span><span class="token number">0001</span><span class="token punctuation">;</span>
<span class="token keyword">SET</span> f <span class="token operator">=</span> f <span class="token operator">+</span> <span class="token punctuation">.</span><span class="token number">0001E0</span><span class="token punctuation">;</span>
<span class="token keyword">SET</span> i <span class="token operator">=</span> i <span class="token operator">+</span> <span class="token number">1</span><span class="token punctuation">;</span>
<span class="token keyword">END</span> <span class="token keyword">WHILE</span><span class="token punctuation">;</span>
<span class="token keyword">SELECT</span> d<span class="token punctuation">,</span> f<span class="token punctuation">;</span>
<span class="token keyword">END</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
The sum for both
<code class="literal">
d
</code>
and
<code class="literal">
f
</code>
logically should be 1, but that is true only for the decimal
calculation. The floating-point calculation introduces small
errors:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-none"><div class="docs-select-all right" id="sa57625981"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-none">+--------+------------------+
| d | f |
+--------+------------------+
| 1.0000 | 0.99999999999991 |
+--------+------------------+</code></pre>
</div>
<p>
<span class="bold">
<strong>
Example 2
</strong>
</span>
. Multiplication is
performed with the scale required by standard SQL. That is, for
two numbers
<em class="replaceable">
<code>
X1
</code>
</em>
and
<em class="replaceable">
<code>
X2
</code>
</em>
that have scale
<em class="replaceable">
<code>
S1
</code>
</em>
and
<em class="replaceable">
<code>
S2
</code>
</em>
,
the scale of the result is
<code class="literal">
<em class="replaceable">
<code>
S1
</code>
</em>
+
<em class="replaceable">
<code>
S2
</code>
</em>
</code>
:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa45625717"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token punctuation">.</span><span class="token number">01</span> <span class="token operator">*</span> <span class="token punctuation">.</span><span class="token number">01</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> .01 * .01 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> 0.0001 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span></code></pre>
</div>
<p>
<span class="bold">
<strong>
Example 3
</strong>
</span>
. Rounding behavior for
exact-value numbers is well-defined:
</p>
<p>
Rounding behavior (for example, with the
<a class="link" href="mathematical-functions.html#function_round">
<code class="literal">
ROUND()
</code>
</a>
function) is independent of
the implementation of the underlying C library, which means that
results are consistent from platform to platform.
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
Rounding for exact-value columns
(
<a class="link" href="fixed-point-types.html" title="13.1.3 Fixed-Point Types (Exact Value) - DECIMAL, NUMERIC">
<code class="literal">
DECIMAL
</code>
</a>
and integer) and
exact-valued numbers uses the
<span class="quote">
“
<span class="quote">
round half away from
zero
</span>
”
</span>
rule. A value with a fractional part of .5 or
greater is rounded away from zero to the nearest integer, as
shown here:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa67259363"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token function">ROUND</span><span class="token punctuation">(</span><span class="token number">2.5</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token function">ROUND</span><span class="token punctuation">(</span><span class="token operator">-</span><span class="token number">2.5</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> ROUND(2.5) <span class="token punctuation">|</span> ROUND(<span class="token punctuation">-</span>2.5) <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> 3 <span class="token punctuation">|</span> <span class="token punctuation">-</span>3 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span></code></pre>
</div>
</li>
<li class="listitem">
<p>
Rounding for floating-point values uses the C library, which
on many systems uses the
<span class="quote">
“
<span class="quote">
round to nearest even
</span>
”
</span>
rule. A value with a fractional part exactly half way between
two integers is rounded to the nearest even integer:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa49918910"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token function">ROUND</span><span class="token punctuation">(</span><span class="token number">2.5E0</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token function">ROUND</span><span class="token punctuation">(</span><span class="token operator">-</span><span class="token number">2.5E0</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> ROUND(2.5E0) <span class="token punctuation">|</span> ROUND(<span class="token punctuation">-</span>2.5E0) <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> 2 <span class="token punctuation">|</span> <span class="token punctuation">-</span>2 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span></code></pre>
</div>
</li>
</ul>
</div>
<p>
<span class="bold">
<strong>
Example 4
</strong>
</span>
. In strict mode,
inserting a value that is out of range for a column causes an
error, rather than truncation to a legal value.
</p>
<p>
When MySQL is not running in strict mode, truncation to a legal
value occurs:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa5625128"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SET</span> sql_mode<span class="token operator">=</span><span class="token string">''</span><span class="token punctuation">;</span>
<span class="token output">Query OK, 0 rows affected (0.00 sec)</span>
<span class="token prompt">mysql></span> <span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> t <span class="token punctuation">(</span>i <span class="token datatype">TINYINT</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token output">Query OK, 0 rows affected (0.01 sec)</span>
<span class="token prompt">mysql></span> <span class="token keyword">INSERT</span> <span class="token keyword">INTO</span> t <span class="token keyword">SET</span> i <span class="token operator">=</span> <span class="token number">128</span><span class="token punctuation">;</span>
<span class="token output">Query OK, 1 row affected, 1 warning (0.00 sec)</span>
<span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> i <span class="token keyword">FROM</span> t<span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> i <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> 127 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output">1 row in set (0.00 sec)</span></code></pre>
</div>
<p>
However, an error occurs if strict mode is in effect:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa68944392"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SET</span> sql_mode<span class="token operator">=</span><span class="token string">'STRICT_ALL_TABLES'</span><span class="token punctuation">;</span>
<span class="token output">Query OK, 0 rows affected (0.00 sec)</span>
<span class="token prompt">mysql></span> <span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> t <span class="token punctuation">(</span>i <span class="token datatype">TINYINT</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token output">Query OK, 0 rows affected (0.00 sec)</span>
<span class="token prompt">mysql></span> <span class="token keyword">INSERT</span> <span class="token keyword">INTO</span> t <span class="token keyword">SET</span> i <span class="token operator">=</span> <span class="token number">128</span><span class="token punctuation">;</span>
<span class="token output">ERROR 1264 (22003)<span class="token punctuation">:</span> Out of range value adjusted for column 'i' at row 1
</span>
<span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> i <span class="token keyword">FROM</span> t<span class="token punctuation">;</span>
<span class="token output">Empty set (0.00 sec)</span></code></pre>
</div>
<p>
<span class="bold">
<strong>
Example 5
</strong>
</span>
: In strict mode and
with
<a class="link" href="sql-mode.html#sqlmode_error_for_division_by_zero">
<code class="literal">
ERROR_FOR_DIVISION_BY_ZERO
</code>
</a>
set, division by zero causes an error, not a result of
<code class="literal">
NULL
</code>
.
</p>
<p>
In nonstrict mode, division by zero has a result of
<code class="literal">
NULL
</code>
:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa49609420"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SET</span> sql_mode<span class="token operator">=</span><span class="token string">''</span><span class="token punctuation">;</span>
<span class="token output">Query OK, 0 rows affected (0.01 sec)</span>
<span class="token prompt">mysql></span> <span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> t <span class="token punctuation">(</span>i <span class="token datatype">TINYINT</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token output">Query OK, 0 rows affected (0.00 sec)</span>
<span class="token prompt">mysql></span> <span class="token keyword">INSERT</span> <span class="token keyword">INTO</span> t <span class="token keyword">SET</span> i <span class="token operator">=</span> <span class="token number">1</span> <span class="token operator">/</span> <span class="token number">0</span><span class="token punctuation">;</span>
<span class="token output">Query OK, 1 row affected (0.00 sec)</span>
<span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> i <span class="token keyword">FROM</span> t<span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> i <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> NULL <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output">1 row in set (0.03 sec)</span></code></pre>
</div>
<p>
However, division by zero is an error if the proper SQL modes are
in effect:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa75695552"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SET</span> sql_mode<span class="token operator">=</span><span class="token string">'STRICT_ALL_TABLES,ERROR_FOR_DIVISION_BY_ZERO'</span><span class="token punctuation">;</span>
<span class="token output">Query OK, 0 rows affected (0.00 sec)</span>
<span class="token prompt">mysql></span> <span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> t <span class="token punctuation">(</span>i <span class="token datatype">TINYINT</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token output">Query OK, 0 rows affected (0.00 sec)</span>
<span class="token prompt">mysql></span> <span class="token keyword">INSERT</span> <span class="token keyword">INTO</span> t <span class="token keyword">SET</span> i <span class="token operator">=</span> <span class="token number">1</span> <span class="token operator">/</span> <span class="token number">0</span><span class="token punctuation">;</span>
<span class="token output">ERROR 1365 (22012)<span class="token punctuation">:</span> Division by 0
</span>
<span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> i <span class="token keyword">FROM</span> t<span class="token punctuation">;</span>
<span class="token output">Empty set (0.01 sec)</span></code></pre>
</div>
<p>
<span class="bold">
<strong>
Example 6
</strong>
</span>
. Exact-value literals
are evaluated as exact values.
</p>
<p>
Approximate-value literals are evaluated using floating point, but
exact-value literals are handled as
<a class="link" href="fixed-point-types.html" title="13.1.3 Fixed-Point Types (Exact Value) - DECIMAL, NUMERIC">
<code class="literal">
DECIMAL
</code>
</a>
:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa70545305"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> t <span class="token keyword">SELECT</span> <span class="token number">2.5</span> <span class="token keyword">AS</span> a<span class="token punctuation">,</span> <span class="token number">25E</span><span class="token operator">-</span><span class="token number">1</span> <span class="token keyword">AS</span> b<span class="token punctuation">;</span>
<span class="token output">Query OK, 1 row affected (0.01 sec)</span>
<span class="token output">Records: 1 Duplicates: 0 Warnings: 0</span>
<span class="token prompt">mysql></span> <span class="token keyword">DESCRIBE</span> t<span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> Field <span class="token punctuation">|</span> Type <span class="token punctuation">|</span> Null <span class="token punctuation">|</span> Key <span class="token punctuation">|</span> Default <span class="token punctuation">|</span> Extra <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> a <span class="token punctuation">|</span> decimal(2,1) unsigned <span class="token punctuation">|</span> NO <span class="token punctuation">|</span> <span class="token punctuation">|</span> 0.0 <span class="token punctuation">|</span> <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> b <span class="token punctuation">|</span> double <span class="token punctuation">|</span> NO <span class="token punctuation">|</span> <span class="token punctuation">|</span> 0 <span class="token punctuation">|</span> <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output">2 rows in set (0.01 sec)</span></code></pre>
</div>
<p>
<span class="bold">
<strong>
Example 7
</strong>
</span>
. If the argument to an
aggregate function is an exact numeric type, the result is also an
exact numeric type, with a scale at least that of the argument.
</p>
<p>
Consider these statements:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa78550348"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> t <span class="token punctuation">(</span>i <span class="token datatype">INT</span><span class="token punctuation">,</span> d <span class="token datatype">DECIMAL</span><span class="token punctuation">,</span> f <span class="token datatype">FLOAT</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token prompt">mysql></span> <span class="token keyword">INSERT</span> <span class="token keyword">INTO</span> t <span class="token keyword">VALUES</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span><span class="token number">1</span><span class="token punctuation">,</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token prompt">mysql></span> <span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> y <span class="token keyword">SELECT</span> <span class="token function">AVG</span><span class="token punctuation">(</span>i<span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token function">AVG</span><span class="token punctuation">(</span>d<span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token function">AVG</span><span class="token punctuation">(</span>f<span class="token punctuation">)</span> <span class="token keyword">FROM</span> t<span class="token punctuation">;</span></code></pre>
</div>
<p>
The result is a double only for the floating-point argument. For
exact type arguments, the result is also an exact type:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa9631639"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">DESCRIBE</span> y<span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> Field <span class="token punctuation">|</span> Type <span class="token punctuation">|</span> Null <span class="token punctuation">|</span> Key <span class="token punctuation">|</span> Default <span class="token punctuation">|</span> Extra <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> AVG(i) <span class="token punctuation">|</span> decimal(14,4) <span class="token punctuation">|</span> YES <span class="token punctuation">|</span> <span class="token punctuation">|</span> NULL <span class="token punctuation">|</span> <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> AVG(d) <span class="token punctuation">|</span> decimal(14,4) <span class="token punctuation">|</span> YES <span class="token punctuation">|</span> <span class="token punctuation">|</span> NULL <span class="token punctuation">|</span> <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> AVG(f) <span class="token punctuation">|</span> double <span class="token punctuation">|</span> YES <span class="token punctuation">|</span> <span class="token punctuation">|</span> NULL <span class="token punctuation">|</span> <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span></code></pre>
</div>
<p>
The result is a double only for the floating-point argument. For
exact type arguments, the result is also an exact type.
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/partitioning-key.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="partitioning-key">
</a>
26.2.5 KEY Partitioning
</h3>
</div>
</div>
</div>
<a class="indexterm" name="idm46045084229888">
</a>
<a class="indexterm" name="idm46045084228400">
</a>
<p>
Partitioning by key is similar to partitioning by hash, except
that where hash partitioning employs a user-defined expression,
the hashing function for key partitioning is supplied by the
MySQL server. NDB Cluster uses
<a class="link" href="encryption-functions.html#function_md5">
<code class="literal">
MD5()
</code>
</a>
for this purpose; for
tables using other storage engines, the server employs its own
internal hashing function.
</p>
<p>
The syntax rules for
<code class="literal">
CREATE TABLE ... PARTITION BY
KEY
</code>
are similar to those for creating a table that is
partitioned by hash. The major differences are listed here:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<code class="literal">
KEY
</code>
is used rather than
<code class="literal">
HASH
</code>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
KEY
</code>
takes only a list of zero or more
column names. Any columns used as the partitioning key must
comprise part or all of the table's primary key, if the
table has one. Where no column name is specified as the
partitioning key, the table's primary key is used, if
there is one. For example, the following
<a class="link" href="create-table.html" title="15.1.20 CREATE TABLE Statement">
<code class="literal">
CREATE TABLE
</code>
</a>
statement is
valid in MySQL 8.4:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa60316687"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> k1 <span class="token punctuation">(</span>
id <span class="token datatype">INT</span> <span class="token operator">NOT</span> <span class="token boolean">NULL</span> <span class="token keyword">PRIMARY</span> <span class="token keyword">KEY</span><span class="token punctuation">,</span>
<span class="token keyword">name</span> <span class="token datatype">VARCHAR</span><span class="token punctuation">(</span><span class="token number">20</span><span class="token punctuation">)</span>
<span class="token punctuation">)</span>
<span class="token keyword">PARTITION</span> <span class="token keyword">BY</span> <span class="token keyword">KEY</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
<span class="token keyword">PARTITIONS</span> <span class="token number">2</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
If there is no primary key but there is a unique key, then
the unique key is used for the partitioning key:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa66020192"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> k1 <span class="token punctuation">(</span>
id <span class="token datatype">INT</span> <span class="token operator">NOT</span> <span class="token boolean">NULL</span><span class="token punctuation">,</span>
<span class="token keyword">name</span> <span class="token datatype">VARCHAR</span><span class="token punctuation">(</span><span class="token number">20</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
<span class="token keyword">UNIQUE</span> <span class="token keyword">KEY</span> <span class="token punctuation">(</span>id<span class="token punctuation">)</span>
<span class="token punctuation">)</span>
<span class="token keyword">PARTITION</span> <span class="token keyword">BY</span> <span class="token keyword">KEY</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
<span class="token keyword">PARTITIONS</span> <span class="token number">2</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
However, if the unique key column were not defined as
<code class="literal">
NOT NULL
</code>
, then the previous statement
would fail.
</p>
<p>
In both of these cases, the partitioning key is the
<code class="literal">
id
</code>
column, even though it is not shown in
the output of
<a class="link" href="show-create-table.html" title="15.7.7.11 SHOW CREATE TABLE Statement">
<code class="literal">
SHOW CREATE
TABLE
</code>
</a>
or in the
<code class="literal">
PARTITION_EXPRESSION
</code>
column of the
Information Schema
<a class="link" href="information-schema-partitions-table.html" title="28.3.21 The INFORMATION_SCHEMA PARTITIONS Table">
<code class="literal">
PARTITIONS
</code>
</a>
table.
</p>
<p>
Unlike the case with other partitioning types, columns used
for partitioning by
<code class="literal">
KEY
</code>
are not
restricted to integer or
<code class="literal">
NULL
</code>
values. For
example, the following
<a class="link" href="create-table.html" title="15.1.20 CREATE TABLE Statement">
<code class="literal">
CREATE
TABLE
</code>
</a>
statement is valid:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa22081734"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> tm1 <span class="token punctuation">(</span>
s1 <span class="token datatype">CHAR</span><span class="token punctuation">(</span><span class="token number">32</span><span class="token punctuation">)</span> <span class="token keyword">PRIMARY</span> <span class="token keyword">KEY</span>
<span class="token punctuation">)</span>
<span class="token keyword">PARTITION</span> <span class="token keyword">BY</span> <span class="token keyword">KEY</span><span class="token punctuation">(</span>s1<span class="token punctuation">)</span>
<span class="token keyword">PARTITIONS</span> <span class="token number">10</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
The preceding statement would
<span class="emphasis">
<em>
not
</em>
</span>
be
valid, were a different partitioning type to be specified.
(In this case, simply using
<code class="literal">
PARTITION BY
KEY()
</code>
would also be valid and have the same effect
as
<code class="literal">
PARTITION BY KEY(s1)
</code>
, since
<code class="literal">
s1
</code>
is the table's primary key.)
</p>
<p>
For additional information about this issue, see
<a class="xref" href="partitioning-limitations.html" title="26.6 Restrictions and Limitations on Partitioning">
Section 26.6, “Restrictions and Limitations on Partitioning”
</a>
.
</p>
<p>
Columns with index prefixes are not supported in
partitioning keys. This means that
<a class="link" href="char.html" title="13.3.2 The CHAR and VARCHAR Types">
<code class="literal">
CHAR
</code>
</a>
,
<a class="link" href="char.html" title="13.3.2 The CHAR and VARCHAR Types">
<code class="literal">
VARCHAR
</code>
</a>
,
<a class="link" href="binary-varbinary.html" title="13.3.3 The BINARY and VARBINARY Types">
<code class="literal">
BINARY
</code>
</a>
, and
<a class="link" href="binary-varbinary.html" title="13.3.3 The BINARY and VARBINARY Types">
<code class="literal">
VARBINARY
</code>
</a>
columns can be used
in a partitioning key, as long as they do not employ
prefixes; because a prefix must be specified for
<a class="link" href="blob.html" title="13.3.4 The BLOB and TEXT Types">
<code class="literal">
BLOB
</code>
</a>
and
<a class="link" href="blob.html" title="13.3.4 The BLOB and TEXT Types">
<code class="literal">
TEXT
</code>
</a>
columns in index
definitions, it is not possible to use columns of these two
types in partitioning keys. In older versions of MySQL,
columns using prefixes were permitted when creating,
altering, or upgrading a partitioned table, even though they
were not included in the table's partitioning key; in
MySQL 8.4, this is no longer allowed
deprecated, and the server rejects any
<a class="link" href="create-table.html" title="15.1.20 CREATE TABLE Statement">
<code class="literal">
CREATE TABLE
</code>
</a>
or
<a class="link" href="alter-table.html" title="15.1.9 ALTER TABLE Statement">
<code class="literal">
ALTER TABLE
</code>
</a>
statement
affecting a partitioned table in which one or more columns
using prefixes occur with an error. See
<a class="xref" href="partitioning-limitations.html#partitioning-limitations-prefixes" title="Column index prefixes not supported for key partitioning">
Column index prefixes not supported for key partitioning
</a>
.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
Tables using the
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDB
</code>
</a>
storage
engine are implicitly partitioned by
<code class="literal">
KEY
</code>
, using the table's primary key
as the partitioning key (as with other MySQL storage
engines). In the event that the NDB Cluster table has no
explicit primary key, the
<span class="quote">
“
<span class="quote">
hidden
</span>
”
</span>
primary
key generated by the
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDB
</code>
</a>
storage engine for each NDB Cluster table is used as the
partitioning key.
</p>
<p>
If you define an explicit partitioning scheme for an
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDB
</code>
</a>
table, the table must
have an explicit primary key, and any columns used in the
partitioning expression must be part of this key. However,
if the table uses an
<span class="quote">
“
<span class="quote">
empty
</span>
”
</span>
partitioning
expression—that is,
<code class="literal">
PARTITION BY
KEY()
</code>
with no column references—then no
explicit primary key is required.
</p>
<p>
You can observe this partitioning using the
<a class="link" href="mysql-cluster-programs-ndb-desc.html" title="25.5.9 ndb_desc — Describe NDB Tables">
<span class="command">
<strong>
ndb_desc
</strong>
</span>
</a>
utility (with the
<code class="option">
-p
</code>
option).
</p>
</div>
<div class="important" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Important
</div>
<p>
For a key-partitioned table, you cannot execute an
<code class="literal">
ALTER TABLE DROP PRIMARY KEY
</code>
, as doing
so generates the error
<span class="errortext">
ERROR 1466 (HY000):
Field in list of fields for partition function not found
in table
</span>
. This is not an issue for NDB Cluster
tables which are partitioned by
<code class="literal">
KEY
</code>
; in
such cases, the table is reorganized using the
<span class="quote">
“
<span class="quote">
hidden
</span>
”
</span>
primary key as the table's new
partitioning key. See
<a class="xref" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
Chapter 25,
<i>
MySQL NDB Cluster 8.4
</i>
</a>
.
</p>
</div>
</li>
</ul>
</div>
<a class="indexterm" name="idm46045084175216">
</a>
<a class="indexterm" name="idm46045084173728">
</a>
<p>
It is also possible to partition a table by linear key. Here is
a simple example:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa90109736"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> tk <span class="token punctuation">(</span>
col1 <span class="token datatype">INT</span> <span class="token operator">NOT</span> <span class="token boolean">NULL</span><span class="token punctuation">,</span>
col2 <span class="token datatype">CHAR</span><span class="token punctuation">(</span><span class="token number">5</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
col3 <span class="token datatype">DATE</span>
<span class="token punctuation">)</span>
<span class="token keyword">PARTITION</span> <span class="token keyword">BY</span> <span class="token keyword">LINEAR</span> <span class="token keyword">KEY</span> <span class="token punctuation">(</span>col1<span class="token punctuation">)</span>
<span class="token keyword">PARTITIONS</span> <span class="token number">3</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
The
<code class="literal">
LINEAR
</code>
keyword has the same effect on
<code class="literal">
KEY
</code>
partitioning as it does on
<code class="literal">
HASH
</code>
partitioning, with the partition number
being derived using a powers-of-two algorithm rather than modulo
arithmetic. See
<a class="xref" href="partitioning-linear-hash.html" title="26.2.4.1 LINEAR HASH Partitioning">
Section 26.2.4.1, “LINEAR HASH Partitioning”
</a>
, for
a description of this algorithm and its implications.
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/performance-schema-telemetry-tables.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="performance-schema-telemetry-tables">
</a>
29.12.21 Performance Schema Telemetry Tables
</h3>
</div>
</div>
</div>
<div class="toc">
<dl class="toc">
<dt>
<span class="section">
<a href="performance-schema-setup-meters-table.html">
29.12.21.1 The setup_meters Table
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="performance-schema-setup-metrics-table.html">
29.12.21.2 The setup_metrics Table
</a>
</span>
</dt>
</dl>
</div>
<p>
The following sections describe tables associated with the
Telemetry services:
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/mysql-cluster-ndbinfo-cpustat.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="mysql-cluster-ndbinfo-cpustat">
</a>
25.6.17.19 The ndbinfo cpustat Table
</h4>
</div>
</div>
</div>
<a class="indexterm" name="idm46045089939872">
</a>
<p>
The
<code class="literal">
cpustat
</code>
table provides per-thread CPU
statistics gathered each second, for each thread running in the
<code class="literal">
NDB
</code>
kernel.
</p>
<p>
The
<code class="literal">
cpustat
</code>
table contains the following
columns:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<code class="literal">
node_id
</code>
</p>
<p>
ID of the node where the thread is running
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
thr_no
</code>
</p>
<p>
Thread ID (specific to this node)
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
OS_user
</code>
</p>
<p>
OS user time
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
OS_system
</code>
</p>
<p>
OS system time
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
OS_idle
</code>
</p>
<p>
OS idle time
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
thread_exec
</code>
</p>
<p>
Thread execution time
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
thread_sleeping
</code>
</p>
<p>
Thread sleep time
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
thread_spinning
</code>
</p>
<p>
Thread spin time
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
thread_send
</code>
</p>
<p>
Thread send time
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
thread_buffer_full
</code>
</p>
<p>
Thread buffer full time
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
elapsed_time
</code>
</p>
<p>
Elapsed time
</p>
</li>
</ul>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/socket-pluggable-authentication.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="socket-pluggable-authentication">
</a>
8.4.1.10 Socket Peer-Credential Pluggable Authentication
</h4>
</div>
</div>
</div>
<a class="indexterm" name="idm46045244161280">
</a>
<a class="indexterm" name="idm46045244160240">
</a>
<p>
The server-side
<code class="literal">
auth_socket
</code>
authentication
plugin authenticates clients that connect from the local host
through the Unix socket file. The plugin uses the
<code class="literal">
SO_PEERCRED
</code>
socket option to obtain
information about the user running the client program. Thus, the
plugin can be used only on systems that support the
<code class="literal">
SO_PEERCRED
</code>
option, such as Linux.
</p>
<p>
The source code for this plugin can be examined as a relatively
simple example demonstrating how to write a loadable
authentication plugin.
</p>
<p>
The following table shows the plugin and library file names. The
file must be located in the directory named by the
<a class="link" href="server-system-variables.html#sysvar_plugin_dir">
<code class="literal">
plugin_dir
</code>
</a>
system variable.
</p>
<div class="table">
<a name="idm46045244153488">
</a>
<p class="title">
<b>
Table 8.25 Plugin and Library Names for Socket Peer-Credential Authentication
</b>
</p>
<div class="table-contents">
<table summary="Names for the plugins and library file used for socket peer-credential password authentication.">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<thead>
<tr>
<th>
Plugin or File
</th>
<th>
Plugin or File Name
</th>
</tr>
</thead>
<tbody>
<tr>
<td>
Server-side plugin
</td>
<td>
<code class="literal">
auth_socket
</code>
</td>
</tr>
<tr>
<td>
Client-side plugin
</td>
<td>
None, see discussion
</td>
</tr>
<tr>
<td>
Library file
</td>
<td>
<code class="filename">
auth_socket.so
</code>
</td>
</tr>
</tbody>
</table>
</div>
</div>
<br class="table-break"/>
<p>
The following sections provide installation and usage
information specific to socket pluggable authentication:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<a class="xref" href="socket-pluggable-authentication.html#socket-pluggable-authentication-installation" title="Installing Socket Pluggable Authentication">
Installing Socket Pluggable Authentication
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="socket-pluggable-authentication.html#socket-pluggable-authentication-uninstallation" title="Uninstalling Socket Pluggable Authentication">
Uninstalling Socket Pluggable Authentication
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="socket-pluggable-authentication.html#socket-pluggable-authentication-usage" title="Using Socket Pluggable Authentication">
Using Socket Pluggable Authentication
</a>
</p>
</li>
</ul>
</div>
<p>
For general information about pluggable authentication in MySQL,
see
<a class="xref" href="pluggable-authentication.html" title="8.2.17 Pluggable Authentication">
Section 8.2.17, “Pluggable Authentication”
</a>
.
</p>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h5 class="title">
<a name="socket-pluggable-authentication-installation">
</a>
Installing Socket Pluggable Authentication
</h5>
</div>
</div>
</div>
<p>
This section describes how to install the socket
authentication plugin. For general information about
installing plugins, see
<a class="xref" href="plugin-loading.html" title="7.6.1 Installing and Uninstalling Plugins">
Section 7.6.1, “Installing and Uninstalling Plugins”
</a>
.
</p>
<p>
To be usable by the server, the plugin library file must be
located in the MySQL plugin directory (the directory named by
the
<a class="link" href="server-system-variables.html#sysvar_plugin_dir">
<code class="literal">
plugin_dir
</code>
</a>
system
variable). If necessary, configure the plugin directory
location by setting the value of
<a class="link" href="server-system-variables.html#sysvar_plugin_dir">
<code class="literal">
plugin_dir
</code>
</a>
at server startup.
</p>
<p>
To load the plugin at server startup, use the
<a class="link" href="server-options.html#option_mysqld_plugin-load-add">
<code class="option">
--plugin-load-add
</code>
</a>
option to
name the library file that contains it. With this
plugin-loading method, the option must be given each time the
server starts. For example, put these lines in the server
<code class="filename">
my.cnf
</code>
file:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-ini"><div class="docs-select-all right" id="sa11859201"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-ini"><span class="token selector">[mysqld]</span>
<span class="token constant">plugin-load-add</span><span class="token attr-value"><span class="token punctuation">=</span>auth_socket.so</span></code></pre>
</div>
<p>
After modifying
<code class="filename">
my.cnf
</code>
, restart the
server to cause the new settings to take effect.
</p>
<p>
Alternatively, to load the plugin at runtime, use this
statement:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa13009236"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">INSTALL</span> <span class="token keyword">PLUGIN</span> auth_socket <span class="token keyword">SONAME</span> <span class="token string">'auth_socket.so'</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
<a class="link" href="install-plugin.html" title="15.7.4.4 INSTALL PLUGIN Statement">
<code class="literal">
INSTALL PLUGIN
</code>
</a>
loads the plugin
immediately, and also registers it in the
<code class="literal">
mysql.plugins
</code>
system table to cause the
server to load it for each subsequent normal startup without
the need for
<a class="link" href="server-options.html#option_mysqld_plugin-load-add">
<code class="option">
--plugin-load-add
</code>
</a>
.
</p>
<p>
To verify plugin installation, examine the Information Schema
<a class="link" href="information-schema-plugins-table.html" title="28.3.22 The INFORMATION_SCHEMA PLUGINS Table">
<code class="literal">
PLUGINS
</code>
</a>
table or use the
<a class="link" href="show-plugins.html" title="15.7.7.27 SHOW PLUGINS Statement">
<code class="literal">
SHOW PLUGINS
</code>
</a>
statement (see
<a class="xref" href="obtaining-plugin-information.html" title="7.6.2 Obtaining Server Plugin Information">
Section 7.6.2, “Obtaining Server Plugin Information”
</a>
). For example:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa39944415"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> PLUGIN_NAME<span class="token punctuation">,</span> PLUGIN_STATUS
<span class="token keyword">FROM</span> INFORMATION_SCHEMA<span class="token punctuation">.</span><span class="token keyword">PLUGINS</span>
<span class="token keyword">WHERE</span> PLUGIN_NAME <span class="token operator">LIKE</span> <span class="token string">'%socket%'</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> PLUGIN_NAME <span class="token punctuation">|</span> PLUGIN_STATUS <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> auth_socket <span class="token punctuation">|</span> ACTIVE <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span></code></pre>
</div>
<p>
If the plugin fails to initialize, check the server error log
for diagnostic messages.
</p>
<p>
To associate MySQL accounts with the socket plugin, see
<a class="xref" href="socket-pluggable-authentication.html#socket-pluggable-authentication-usage" title="Using Socket Pluggable Authentication">
Using Socket Pluggable Authentication
</a>
.
</p>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h5 class="title">
<a name="socket-pluggable-authentication-uninstallation">
</a>
Uninstalling Socket Pluggable Authentication
</h5>
</div>
</div>
</div>
<p>
The method used to uninstall the socket authentication plugin
depends on how you installed it:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
If you installed the plugin at server startup using a
<a class="link" href="server-options.html#option_mysqld_plugin-load-add">
<code class="option">
--plugin-load-add
</code>
</a>
option,
restart the server without the option.
</p>
</li>
<li class="listitem">
<p>
If you installed the plugin at runtime using an
<a class="link" href="install-plugin.html" title="15.7.4.4 INSTALL PLUGIN Statement">
<code class="literal">
INSTALL PLUGIN
</code>
</a>
statement,
it remains installed across server restarts. To uninstall
it, use
<a class="link" href="uninstall-plugin.html" title="15.7.4.6 UNINSTALL PLUGIN Statement">
<code class="literal">
UNINSTALL PLUGIN
</code>
</a>
:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa8158676"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">UNINSTALL</span> <span class="token keyword">PLUGIN</span> auth_socket<span class="token punctuation">;</span></code></pre>
</div>
</li>
</ul>
</div>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h5 class="title">
<a name="socket-pluggable-authentication-usage">
</a>
Using Socket Pluggable Authentication
</h5>
</div>
</div>
</div>
<p>
The socket plugin checks whether the socket user name (the
operating system user name) matches the MySQL user name
specified by the client program to the server. If the names do
not match, the plugin checks whether the socket user name
matches the name specified in the
<code class="literal">
authentication_string
</code>
column of the
<code class="literal">
mysql.user
</code>
system table row. If a match is
found, the plugin permits the connection. The
<code class="literal">
authentication_string
</code>
value can be
specified using an
<code class="literal">
IDENTIFIED ...AS
</code>
clause
with
<a class="link" href="create-user.html" title="15.7.1.3 CREATE USER Statement">
<code class="literal">
CREATE USER
</code>
</a>
or
<a class="link" href="alter-user.html" title="15.7.1.1 ALTER USER Statement">
<code class="literal">
ALTER USER
</code>
</a>
.
</p>
<p>
Suppose that a MySQL account is created for an operating
system user named
<code class="literal">
valerie
</code>
who is to be
authenticated by the
<code class="literal">
auth_socket
</code>
plugin for
connections from the local host through the socket file:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa50931155"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">USER</span> <span class="token string">'valerie'</span>@<span class="token string">'localhost'</span> <span class="token keyword">IDENTIFIED</span> <span class="token keyword">WITH</span> auth_socket<span class="token punctuation">;</span></code></pre>
</div>
<p>
If a user on the local host with a login name of
<code class="literal">
stefanie
</code>
invokes
<a class="link" href="mysql.html" title="6.5.1 mysql — The MySQL Command-Line Client">
<span class="command">
<strong>
mysql
</strong>
</span>
</a>
with the option
<code class="option">
--user=valerie
</code>
to connect
through the socket file, the server uses
<code class="literal">
auth_socket
</code>
to authenticate the client. The
plugin determines that the
<code class="option">
--user
</code>
option
value (
<code class="literal">
valerie
</code>
) differs from the client
user's name (
<code class="literal">
stephanie
</code>
) and refuses
the connection. If a user named
<code class="literal">
valerie
</code>
tries the same thing, the plugin finds that the user name and
the MySQL user name are both
<code class="literal">
valerie
</code>
and
permits the connection. However, the plugin refuses the
connection even for
<code class="literal">
valerie
</code>
if the
connection is made using a different protocol, such as TCP/IP.
</p>
<p>
To permit both the
<code class="literal">
valerie
</code>
and
<code class="literal">
stephanie
</code>
operating system users to access
MySQL through socket file connections that use the account,
this can be done two ways:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
Name both users at account-creation time, one following
<a class="link" href="create-user.html" title="15.7.1.3 CREATE USER Statement">
<code class="literal">
CREATE USER
</code>
</a>
, and the other
in the authentication string:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa86371581"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">USER</span> <span class="token string">'valerie'</span>@<span class="token string">'localhost'</span> <span class="token keyword">IDENTIFIED</span> <span class="token keyword">WITH</span> auth_socket <span class="token keyword">AS</span> <span class="token string">'stephanie'</span><span class="token punctuation">;</span></code></pre>
</div>
</li>
<li class="listitem">
<p>
If you have already used
<a class="link" href="create-user.html" title="15.7.1.3 CREATE USER Statement">
<code class="literal">
CREATE
USER
</code>
</a>
to create the account for a single user,
use
<a class="link" href="alter-user.html" title="15.7.1.1 ALTER USER Statement">
<code class="literal">
ALTER USER
</code>
</a>
to add the
second user:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa34583903"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">USER</span> <span class="token string">'valerie'</span>@<span class="token string">'localhost'</span> <span class="token keyword">IDENTIFIED</span> <span class="token keyword">WITH</span> auth_socket<span class="token punctuation">;</span>
<span class="token keyword">ALTER</span> <span class="token keyword">USER</span> <span class="token string">'valerie'</span>@<span class="token string">'localhost'</span> <span class="token keyword">IDENTIFIED</span> <span class="token keyword">WITH</span> auth_socket <span class="token keyword">AS</span> <span class="token string">'stephanie'</span><span class="token punctuation">;</span></code></pre>
</div>
</li>
</ul>
</div>
<p>
To access the account, both
<code class="literal">
valerie
</code>
and
<code class="literal">
stephanie
</code>
specify
<code class="option">
--user=valerie
</code>
at connect time.
</p>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/performance-schema-object-filtering.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="performance-schema-object-filtering">
</a>
29.4.5 Pre-Filtering by Object
</h3>
</div>
</div>
</div>
<p>
The
<a class="link" href="performance-schema-setup-objects-table.html" title="29.12.2.4 The setup_objects Table">
<code class="literal">
setup_objects
</code>
</a>
table controls
whether the Performance Schema monitors particular table and
stored program objects. The initial
<a class="link" href="performance-schema-setup-objects-table.html" title="29.12.2.4 The setup_objects Table">
<code class="literal">
setup_objects
</code>
</a>
contents look like
this:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa86391689"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> performance_schema<span class="token punctuation">.</span>setup_objects<span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> OBJECT_TYPE <span class="token punctuation">|</span> OBJECT_SCHEMA <span class="token punctuation">|</span> OBJECT_NAME <span class="token punctuation">|</span> ENABLED <span class="token punctuation">|</span> TIMED <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> EVENT <span class="token punctuation">|</span> mysql <span class="token punctuation">|</span> % <span class="token punctuation">|</span> NO <span class="token punctuation">|</span> NO <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> EVENT <span class="token punctuation">|</span> performance_schema <span class="token punctuation">|</span> % <span class="token punctuation">|</span> NO <span class="token punctuation">|</span> NO <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> EVENT <span class="token punctuation">|</span> information_schema <span class="token punctuation">|</span> % <span class="token punctuation">|</span> NO <span class="token punctuation">|</span> NO <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> EVENT <span class="token punctuation">|</span> % <span class="token punctuation">|</span> % <span class="token punctuation">|</span> YES <span class="token punctuation">|</span> YES <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> FUNCTION <span class="token punctuation">|</span> mysql <span class="token punctuation">|</span> % <span class="token punctuation">|</span> NO <span class="token punctuation">|</span> NO <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> FUNCTION <span class="token punctuation">|</span> performance_schema <span class="token punctuation">|</span> % <span class="token punctuation">|</span> NO <span class="token punctuation">|</span> NO <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> FUNCTION <span class="token punctuation">|</span> information_schema <span class="token punctuation">|</span> % <span class="token punctuation">|</span> NO <span class="token punctuation">|</span> NO <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> FUNCTION <span class="token punctuation">|</span> % <span class="token punctuation">|</span> % <span class="token punctuation">|</span> YES <span class="token punctuation">|</span> YES <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> PROCEDURE <span class="token punctuation">|</span> mysql <span class="token punctuation">|</span> % <span class="token punctuation">|</span> NO <span class="token punctuation">|</span> NO <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> PROCEDURE <span class="token punctuation">|</span> performance_schema <span class="token punctuation">|</span> % <span class="token punctuation">|</span> NO <span class="token punctuation">|</span> NO <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> PROCEDURE <span class="token punctuation">|</span> information_schema <span class="token punctuation">|</span> % <span class="token punctuation">|</span> NO <span class="token punctuation">|</span> NO <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> PROCEDURE <span class="token punctuation">|</span> % <span class="token punctuation">|</span> % <span class="token punctuation">|</span> YES <span class="token punctuation">|</span> YES <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> TABLE <span class="token punctuation">|</span> mysql <span class="token punctuation">|</span> % <span class="token punctuation">|</span> NO <span class="token punctuation">|</span> NO <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> TABLE <span class="token punctuation">|</span> performance_schema <span class="token punctuation">|</span> % <span class="token punctuation">|</span> NO <span class="token punctuation">|</span> NO <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> TABLE <span class="token punctuation">|</span> information_schema <span class="token punctuation">|</span> % <span class="token punctuation">|</span> NO <span class="token punctuation">|</span> NO <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> TABLE <span class="token punctuation">|</span> % <span class="token punctuation">|</span> % <span class="token punctuation">|</span> YES <span class="token punctuation">|</span> YES <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> TRIGGER <span class="token punctuation">|</span> mysql <span class="token punctuation">|</span> % <span class="token punctuation">|</span> NO <span class="token punctuation">|</span> NO <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> TRIGGER <span class="token punctuation">|</span> performance_schema <span class="token punctuation">|</span> % <span class="token punctuation">|</span> NO <span class="token punctuation">|</span> NO <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> TRIGGER <span class="token punctuation">|</span> information_schema <span class="token punctuation">|</span> % <span class="token punctuation">|</span> NO <span class="token punctuation">|</span> NO <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> TRIGGER <span class="token punctuation">|</span> % <span class="token punctuation">|</span> % <span class="token punctuation">|</span> YES <span class="token punctuation">|</span> YES <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span></code></pre>
</div>
<p>
Modifications to the
<a class="link" href="performance-schema-setup-objects-table.html" title="29.12.2.4 The setup_objects Table">
<code class="literal">
setup_objects
</code>
</a>
table affect object monitoring immediately.
</p>
<p>
The
<code class="literal">
OBJECT_TYPE
</code>
column indicates the type of
object to which a row applies.
<code class="literal">
TABLE
</code>
filtering affects table I/O events
(
<code class="literal">
wait/io/table/sql/handler
</code>
instrument) and
table lock events
(
<code class="literal">
wait/lock/table/sql/handler
</code>
instrument).
</p>
<p>
The
<code class="literal">
OBJECT_SCHEMA
</code>
and
<code class="literal">
OBJECT_NAME
</code>
columns should contain a literal
schema or object name, or
<code class="literal">
'%'
</code>
to match any
name.
</p>
<p>
The
<code class="literal">
ENABLED
</code>
column indicates whether matching
objects are monitored, and
<code class="literal">
TIMED
</code>
indicates
whether to collect timing information. Setting the
<code class="literal">
TIMED
</code>
column affects Performance Schema table
contents as described in
<a class="xref" href="performance-schema-timing.html" title="29.4.1 Performance Schema Event Timing">
Section 29.4.1, “Performance Schema Event Timing”
</a>
.
</p>
<p>
The effect of the default object configuration is to instrument
all objects except those in the
<code class="literal">
mysql
</code>
,
<code class="literal">
INFORMATION_SCHEMA
</code>
, and
<code class="literal">
performance_schema
</code>
databases. (Tables in the
<code class="literal">
INFORMATION_SCHEMA
</code>
database are not
instrumented regardless of the contents of
<a class="link" href="performance-schema-setup-objects-table.html" title="29.12.2.4 The setup_objects Table">
<code class="literal">
setup_objects
</code>
</a>
; the row for
<code class="literal">
information_schema.%
</code>
simply makes this
default explicit.)
</p>
<p>
When the Performance Schema checks for a match in
<a class="link" href="performance-schema-setup-objects-table.html" title="29.12.2.4 The setup_objects Table">
<code class="literal">
setup_objects
</code>
</a>
, it tries to find
more specific matches first. For rows that match a given
<code class="literal">
OBJECT_TYPE
</code>
, the Performance Schema checks
rows in this order:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
Rows with
<code class="literal">
OBJECT_SCHEMA='
<em class="replaceable">
<code>
literal
</code>
</em>
'
</code>
and
<code class="literal">
OBJECT_NAME='
<em class="replaceable">
<code>
literal
</code>
</em>
'
</code>
.
</p>
</li>
<li class="listitem">
<p>
Rows with
<code class="literal">
OBJECT_SCHEMA='
<em class="replaceable">
<code>
literal
</code>
</em>
'
</code>
and
<code class="literal">
OBJECT_NAME='%'
</code>
.
</p>
</li>
<li class="listitem">
<p>
Rows with
<code class="literal">
OBJECT_SCHEMA='%'
</code>
and
<code class="literal">
OBJECT_NAME='%'
</code>
.
</p>
</li>
</ul>
</div>
<p>
For example, with a table
<code class="literal">
db1.t1
</code>
, the
Performance Schema looks in
<code class="literal">
TABLE
</code>
rows for a
match for
<code class="literal">
'db1'
</code>
and
<code class="literal">
't1'
</code>
,
then for
<code class="literal">
'db1'
</code>
and
<code class="literal">
'%'
</code>
,
then for
<code class="literal">
'%'
</code>
and
<code class="literal">
'%'
</code>
. The
order in which matching occurs matters because different
matching
<a class="link" href="performance-schema-setup-objects-table.html" title="29.12.2.4 The setup_objects Table">
<code class="literal">
setup_objects
</code>
</a>
rows can
have different
<code class="literal">
ENABLED
</code>
and
<code class="literal">
TIMED
</code>
values.
</p>
<p>
For table-related events, the Performance Schema combines the
contents of
<a class="link" href="performance-schema-setup-objects-table.html" title="29.12.2.4 The setup_objects Table">
<code class="literal">
setup_objects
</code>
</a>
with
<a class="link" href="performance-schema-setup-instruments-table.html" title="29.12.2.3 The setup_instruments Table">
<code class="literal">
setup_instruments
</code>
</a>
to determine
whether to enable instruments and whether to time enabled
instruments:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
For tables that match a row in
<a class="link" href="performance-schema-setup-objects-table.html" title="29.12.2.4 The setup_objects Table">
<code class="literal">
setup_objects
</code>
</a>
, table
instruments produce events only if
<code class="literal">
ENABLED
</code>
is
<code class="literal">
YES
</code>
in both
<a class="link" href="performance-schema-setup-instruments-table.html" title="29.12.2.3 The setup_instruments Table">
<code class="literal">
setup_instruments
</code>
</a>
and
<a class="link" href="performance-schema-setup-objects-table.html" title="29.12.2.4 The setup_objects Table">
<code class="literal">
setup_objects
</code>
</a>
.
</p>
</li>
<li class="listitem">
<p>
The
<code class="literal">
TIMED
</code>
values in the two tables are
combined, so that timing information is collected only when
both values are
<code class="literal">
YES
</code>
.
</p>
</li>
</ul>
</div>
<p>
For stored program objects, the Performance Schema takes the
<code class="literal">
ENABLED
</code>
and
<code class="literal">
TIMED
</code>
columns
directly from the
<a class="link" href="performance-schema-setup-objects-table.html" title="29.12.2.4 The setup_objects Table">
<code class="literal">
setup_objects
</code>
</a>
row. There is no combining of values with
<a class="link" href="performance-schema-setup-instruments-table.html" title="29.12.2.3 The setup_instruments Table">
<code class="literal">
setup_instruments
</code>
</a>
.
</p>
<p>
Suppose that
<a class="link" href="performance-schema-setup-objects-table.html" title="29.12.2.4 The setup_objects Table">
<code class="literal">
setup_objects
</code>
</a>
contains
the following
<code class="literal">
TABLE
</code>
rows that apply to
<code class="literal">
db1
</code>
,
<code class="literal">
db2
</code>
, and
<code class="literal">
db3
</code>
:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa51963214"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> OBJECT_TYPE <span class="token punctuation">|</span> OBJECT_SCHEMA <span class="token punctuation">|</span> OBJECT_NAME <span class="token punctuation">|</span> ENABLED <span class="token punctuation">|</span> TIMED <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> TABLE <span class="token punctuation">|</span> db1 <span class="token punctuation">|</span> t1 <span class="token punctuation">|</span> YES <span class="token punctuation">|</span> YES <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> TABLE <span class="token punctuation">|</span> db1 <span class="token punctuation">|</span> t2 <span class="token punctuation">|</span> NO <span class="token punctuation">|</span> NO <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> TABLE <span class="token punctuation">|</span> db2 <span class="token punctuation">|</span> % <span class="token punctuation">|</span> YES <span class="token punctuation">|</span> YES <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> TABLE <span class="token punctuation">|</span> db3 <span class="token punctuation">|</span> % <span class="token punctuation">|</span> NO <span class="token punctuation">|</span> NO <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> TABLE <span class="token punctuation">|</span> % <span class="token punctuation">|</span> % <span class="token punctuation">|</span> YES <span class="token punctuation">|</span> YES <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span></code></pre>
</div>
<p>
If an object-related instrument in
<a class="link" href="performance-schema-setup-instruments-table.html" title="29.12.2.3 The setup_instruments Table">
<code class="literal">
setup_instruments
</code>
</a>
has an
<code class="literal">
ENABLED
</code>
value of
<code class="literal">
NO
</code>
,
events for the object are not monitored. If the
<code class="literal">
ENABLED
</code>
value is
<code class="literal">
YES
</code>
,
event monitoring occurs according to the
<code class="literal">
ENABLED
</code>
value in the relevant
<a class="link" href="performance-schema-setup-objects-table.html" title="29.12.2.4 The setup_objects Table">
<code class="literal">
setup_objects
</code>
</a>
row:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<code class="literal">
db1.t1
</code>
events are monitored
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
db1.t2
</code>
events are not monitored
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
db2.t3
</code>
events are monitored
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
db3.t4
</code>
events are not monitored
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
db4.t5
</code>
events are monitored
</p>
</li>
</ul>
</div>
<p>
Similar logic applies for combining the
<code class="literal">
TIMED
</code>
columns from the
<a class="link" href="performance-schema-setup-instruments-table.html" title="29.12.2.3 The setup_instruments Table">
<code class="literal">
setup_instruments
</code>
</a>
and
<a class="link" href="performance-schema-setup-objects-table.html" title="29.12.2.4 The setup_objects Table">
<code class="literal">
setup_objects
</code>
</a>
tables to
determine whether to collect event timing information.
</p>
<p>
If a persistent table and a temporary table have the same name,
matching against
<a class="link" href="performance-schema-setup-objects-table.html" title="29.12.2.4 The setup_objects Table">
<code class="literal">
setup_objects
</code>
</a>
rows
occurs the same way for both. It is not possible to enable
monitoring for one table but not the other. However, each table
is instrumented separately.
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/performance-schema-file-summary-tables.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="performance-schema-file-summary-tables">
</a>
29.12.20.7 File I/O Summary Tables
</h4>
</div>
</div>
</div>
<a class="indexterm" name="idm46045068530848">
</a>
<a class="indexterm" name="idm46045068529392">
</a>
<a class="indexterm" name="idm46045068527888">
</a>
<a class="indexterm" name="idm46045068526384">
</a>
<p>
The Performance Schema maintains file I/O summary tables that
aggregate information about I/O operations.
</p>
<p>
Example file I/O event summary information:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa1491215"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> performance_schema<span class="token punctuation">.</span>file_summary_by_event_name\G
<span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token output"><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span> 2. row <span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span>
EVENT_NAME<span class="token punctuation">:</span> wait/io/file/sql/binlog
COUNT_STAR<span class="token punctuation">:</span> 31
SUM_TIMER_WAIT<span class="token punctuation">:</span> 8243784888
MIN_TIMER_WAIT<span class="token punctuation">:</span> 0
AVG_TIMER_WAIT<span class="token punctuation">:</span> 265928484
MAX_TIMER_WAIT<span class="token punctuation">:</span> 6490658832
...</span>
<span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> performance_schema<span class="token punctuation">.</span>file_summary_by_instance\G
<span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token output"><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span> 2. row <span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span>
FILE_NAME<span class="token punctuation">:</span> /var/mysql/share/english/errmsg.sys
EVENT_NAME<span class="token punctuation">:</span> wait/io/file/sql/ERRMSG
EVENT_NAME<span class="token punctuation">:</span> wait/io/file/sql/ERRMSG
OBJECT_INSTANCE_BEGIN<span class="token punctuation">:</span> 4686193384
COUNT_STAR<span class="token punctuation">:</span> 5
SUM_TIMER_WAIT<span class="token punctuation">:</span> 13990154448
MIN_TIMER_WAIT<span class="token punctuation">:</span> 26349624
AVG_TIMER_WAIT<span class="token punctuation">:</span> 2798030607
MAX_TIMER_WAIT<span class="token punctuation">:</span> 8150662536
...</span></code></pre>
</div>
<p>
Each file I/O summary table has one or more grouping columns
to indicate how the table aggregates events. Event names refer
to names of event instruments in the
<a class="link" href="performance-schema-setup-instruments-table.html" title="29.12.2.3 The setup_instruments Table">
<code class="literal">
setup_instruments
</code>
</a>
table:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<a class="link" href="performance-schema-file-summary-tables.html" title="29.12.20.7 File I/O Summary Tables">
<code class="literal">
file_summary_by_event_name
</code>
</a>
has an
<code class="literal">
EVENT_NAME
</code>
column. Each row
summarizes events for a given event name.
</p>
</li>
<li class="listitem">
<p>
<a class="link" href="performance-schema-file-summary-tables.html" title="29.12.20.7 File I/O Summary Tables">
<code class="literal">
file_summary_by_instance
</code>
</a>
has
<code class="literal">
FILE_NAME
</code>
,
<code class="literal">
EVENT_NAME
</code>
, and
<code class="literal">
OBJECT_INSTANCE_BEGIN
</code>
columns. Each row
summarizes events for a given file and event name.
</p>
</li>
</ul>
</div>
<p>
Each file I/O summary table has the following summary columns
containing aggregated values. Some columns are more general
and have values that are the same as the sum of the values of
more fine-grained columns. In this way, aggregations at higher
levels are available directly without the need for
user-defined views that sum lower-level columns.
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<code class="literal">
COUNT_STAR
</code>
,
<code class="literal">
SUM_TIMER_WAIT
</code>
,
<code class="literal">
MIN_TIMER_WAIT
</code>
,
<code class="literal">
AVG_TIMER_WAIT
</code>
,
<code class="literal">
MAX_TIMER_WAIT
</code>
</p>
<p>
These columns aggregate all I/O operations.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
COUNT_READ
</code>
,
<code class="literal">
SUM_TIMER_READ
</code>
,
<code class="literal">
MIN_TIMER_READ
</code>
,
<code class="literal">
AVG_TIMER_READ
</code>
,
<code class="literal">
MAX_TIMER_READ
</code>
,
<code class="literal">
SUM_NUMBER_OF_BYTES_READ
</code>
</p>
<p>
These columns aggregate all read operations, including
<code class="literal">
FGETS
</code>
,
<code class="literal">
FGETC
</code>
,
<code class="literal">
FREAD
</code>
, and
<code class="literal">
READ
</code>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
COUNT_WRITE
</code>
,
<code class="literal">
SUM_TIMER_WRITE
</code>
,
<code class="literal">
MIN_TIMER_WRITE
</code>
,
<code class="literal">
AVG_TIMER_WRITE
</code>
,
<code class="literal">
MAX_TIMER_WRITE
</code>
,
<code class="literal">
SUM_NUMBER_OF_BYTES_WRITE
</code>
</p>
<p>
These columns aggregate all write operations, including
<code class="literal">
FPUTS
</code>
,
<code class="literal">
FPUTC
</code>
,
<code class="literal">
FPRINTF
</code>
,
<code class="literal">
VFPRINTF
</code>
,
<code class="literal">
FWRITE
</code>
, and
<code class="literal">
PWRITE
</code>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
COUNT_MISC
</code>
,
<code class="literal">
SUM_TIMER_MISC
</code>
,
<code class="literal">
MIN_TIMER_MISC
</code>
,
<code class="literal">
AVG_TIMER_MISC
</code>
,
<code class="literal">
MAX_TIMER_MISC
</code>
</p>
<p>
These columns aggregate all other I/O operations,
including
<code class="literal">
CREATE
</code>
,
<code class="literal">
DELETE
</code>
,
<code class="literal">
OPEN
</code>
,
<code class="literal">
CLOSE
</code>
,
<code class="literal">
STREAM_OPEN
</code>
,
<code class="literal">
STREAM_CLOSE
</code>
,
<code class="literal">
SEEK
</code>
,
<code class="literal">
TELL
</code>
,
<code class="literal">
FLUSH
</code>
,
<code class="literal">
STAT
</code>
,
<code class="literal">
FSTAT
</code>
,
<code class="literal">
CHSIZE
</code>
,
<code class="literal">
RENAME
</code>
, and
<code class="literal">
SYNC
</code>
. There are no byte counts for
these operations.
</p>
</li>
</ul>
</div>
<p>
The file I/O summary tables have these indexes:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<a class="link" href="performance-schema-file-summary-tables.html" title="29.12.20.7 File I/O Summary Tables">
<code class="literal">
file_summary_by_event_name
</code>
</a>
:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<p>
Primary key on (
<code class="literal">
EVENT_NAME
</code>
)
</p>
</li>
</ul>
</div>
</li>
<li class="listitem">
<p>
<a class="link" href="performance-schema-file-summary-tables.html" title="29.12.20.7 File I/O Summary Tables">
<code class="literal">
file_summary_by_instance
</code>
</a>
:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<p>
Primary key on
(
<code class="literal">
OBJECT_INSTANCE_BEGIN
</code>
)
</p>
</li>
<li class="listitem">
<p>
Index on (
<code class="literal">
FILE_NAME
</code>
)
</p>
</li>
<li class="listitem">
<p>
Index on (
<code class="literal">
EVENT_NAME
</code>
)
</p>
</li>
</ul>
</div>
</li>
</ul>
</div>
<p>
<a class="link" href="truncate-table.html" title="15.1.37 TRUNCATE TABLE Statement">
<code class="literal">
TRUNCATE TABLE
</code>
</a>
is permitted for
file I/O summary tables. It resets the summary columns to zero
rather than removing rows.
</p>
<p>
The MySQL server uses several techniques to avoid I/O
operations by caching information read from files, so it is
possible that statements you might expect to result in I/O
events do not do so. You may be able to ensure that I/O does
occur by flushing caches or restarting the server to reset its
state.
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/mysql-cluster-ndbinfo-operations-per-fragment.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="mysql-cluster-ndbinfo-operations-per-fragment">
</a>
25.6.17.49 The ndbinfo operations_per_fragment Table
</h4>
</div>
</div>
</div>
<a class="indexterm" name="idm46045088412016">
</a>
<p>
The
<code class="literal">
operations_per_fragment
</code>
table provides
information about the operations performed on individual
fragments and fragment replicas, as well as about some of the
results from these operations.
</p>
<p>
The
<code class="literal">
operations_per_fragment
</code>
table contains
the following columns:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<code class="literal">
fq_name
</code>
</p>
<p>
Name of this fragment
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
parent_fq_name
</code>
</p>
<p>
Name of this fragment's parent
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
type
</code>
</p>
<p>
Type of object; see text for possible values
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
table_id
</code>
</p>
<p>
Table ID for this table
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
node_id
</code>
</p>
<p>
Node ID for this node
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
block_instance
</code>
</p>
<p>
Kernel block instance ID
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
fragment_num
</code>
</p>
<p>
Fragment ID (number)
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
tot_key_reads
</code>
</p>
<p>
Total number of key reads for this fragment replica
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
tot_key_inserts
</code>
</p>
<p>
Total number of key inserts for this fragment replica
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
tot_key_updates
</code>
</p>
<p>
total number of key updates for this fragment replica
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
tot_key_writes
</code>
</p>
<p>
Total number of key writes for this fragment replica
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
tot_key_deletes
</code>
</p>
<p>
Total number of key deletes for this fragment replica
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
tot_key_refs
</code>
</p>
<p>
Number of key operations refused
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
tot_key_attrinfo_bytes
</code>
</p>
<p>
Total size of all
<code class="literal">
attrinfo
</code>
attributes
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
tot_key_keyinfo_bytes
</code>
</p>
<p>
Total size of all
<code class="literal">
keyinfo
</code>
attributes
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
tot_key_prog_bytes
</code>
</p>
<p>
Total size of all interpreted programs carried by
<code class="literal">
attrinfo
</code>
attributes
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
tot_key_inst_exec
</code>
</p>
<p>
Total number of instructions executed by interpreted
programs for key operations
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
tot_key_bytes_returned
</code>
</p>
<p>
Total size of all data and metadata returned from key read
operations
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
tot_frag_scans
</code>
</p>
<p>
Total number of scans performed on this fragment replica
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
tot_scan_rows_examined
</code>
</p>
<p>
Total number of rows examined by scans
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
tot_scan_rows_returned
</code>
</p>
<p>
Total number of rows returned to client
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
tot_scan_bytes_returned
</code>
</p>
<p>
Total size of data and metadata returned to the client
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
tot_scan_prog_bytes
</code>
</p>
<p>
Total size of interpreted programs for scan operations
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
tot_scan_bound_bytes
</code>
</p>
<p>
Total size of all bounds used in ordered index scans
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
tot_scan_inst_exec
</code>
</p>
<p>
Total number of instructions executed for scans
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
tot_qd_frag_scans
</code>
</p>
<p>
Number of times that scans of this fragment replica have
been queued
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
conc_frag_scans
</code>
</p>
<p>
Number of scans currently active on this fragment replica
(excluding queued scans)
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
conc_qd_frag_scans
</code>
</p>
<p>
Number of scans currently queued for this fragment replica
</p>
</li>
<li class="listitem">
<p>
tot_commits
</p>
<p>
Total number of row changes committed to this fragment
replica
</p>
</li>
</ul>
</div>
<h5>
<a name="idm46045088350224">
</a>
Notes
</h5>
<p>
The
<code class="literal">
fq_name
</code>
contains the fully qualified name
of the schema object to which this fragment replica belongs.
This currently has the following formats:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
Base table:
<code class="literal">
<em class="replaceable">
<code>
DbName
</code>
</em>
/def/
<em class="replaceable">
<code>
TblName
</code>
</em>
</code>
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
BLOB
</code>
table:
<code class="literal">
<em class="replaceable">
<code>
DbName
</code>
</em>
/def/NDB$BLOB_
<em class="replaceable">
<code>
BaseTblId
</code>
</em>
_
<em class="replaceable">
<code>
ColNo
</code>
</em>
</code>
</p>
</li>
<li class="listitem">
<p>
Ordered index:
<code class="literal">
sys/def/
<em class="replaceable">
<code>
BaseTblId
</code>
</em>
/
<em class="replaceable">
<code>
IndexName
</code>
</em>
</code>
</p>
</li>
<li class="listitem">
<p>
Unique index:
<code class="literal">
sys/def/
<em class="replaceable">
<code>
BaseTblId
</code>
</em>
/
<em class="replaceable">
<code>
IndexName
</code>
</em>
$unique
</code>
</p>
</li>
</ul>
</div>
<p>
The
<code class="literal">
$unique
</code>
suffix shown for unique indexes
is added by
<a class="link" href="mysqld.html" title="6.3.1 mysqld — The MySQL Server">
<span class="command">
<strong>
mysqld
</strong>
</span>
</a>
; for an index created by a
different NDB API client application, this may differ, or not be
present.
</p>
<p>
The syntax just shown for fully qualified object names is an
internal interface which is subject to change in future
releases.
</p>
<p>
Consider a table
<code class="literal">
t1
</code>
created and modified by
the following SQL statements:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa96530385"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">DATABASE</span> mydb<span class="token punctuation">;</span>
<span class="token keyword">USE</span> mydb<span class="token punctuation">;</span>
<span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> t1 <span class="token punctuation">(</span>
a <span class="token datatype">INT</span> <span class="token operator">NOT</span> <span class="token boolean">NULL</span><span class="token punctuation">,</span>
b <span class="token datatype">INT</span> <span class="token operator">NOT</span> <span class="token boolean">NULL</span><span class="token punctuation">,</span>
t <span class="token datatype">TEXT</span> <span class="token operator">NOT</span> <span class="token boolean">NULL</span><span class="token punctuation">,</span>
<span class="token keyword">PRIMARY</span> <span class="token keyword">KEY</span> <span class="token punctuation">(</span>b<span class="token punctuation">)</span>
<span class="token punctuation">)</span> <span class="token keyword">ENGINE</span><span class="token operator">=</span><span class="token keyword">ndbcluster</span><span class="token punctuation">;</span>
<span class="token keyword">CREATE</span> <span class="token keyword">UNIQUE</span> <span class="token keyword">INDEX</span> ix1 <span class="token keyword">ON</span> t1<span class="token punctuation">(</span>b<span class="token punctuation">)</span> <span class="token keyword">USING</span> <span class="token keyword">HASH</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
If
<code class="literal">
t1
</code>
is assigned table ID 11, this yields
the
<code class="literal">
fq_name
</code>
values shown here:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
Base table:
<code class="literal">
mydb/def/t1
</code>
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
BLOB
</code>
table:
<code class="literal">
mydb/def/NDB$BLOB_11_2
</code>
</p>
</li>
<li class="listitem">
<p>
Ordered index (primary key):
<code class="literal">
sys/def/11/PRIMARY
</code>
</p>
</li>
<li class="listitem">
<p>
Unique index:
<code class="literal">
sys/def/11/ix1$unique
</code>
</p>
</li>
</ul>
</div>
<p>
For indexes or
<code class="literal">
BLOB
</code>
tables, the
<code class="literal">
parent_fq_name
</code>
column contains the
<code class="literal">
fq_name
</code>
of the corresponding base table. For
base tables, this column is always
<code class="literal">
NULL
</code>
.
</p>
<p>
The
<code class="literal">
type
</code>
column shows the schema object type
used for this fragment, which can take any one of the values
<code class="literal">
System table
</code>
,
<code class="literal">
User table
</code>
,
<code class="literal">
Unique hash index
</code>
, or
<code class="literal">
Ordered
index
</code>
.
<code class="literal">
BLOB
</code>
tables are shown as
<code class="literal">
User table
</code>
.
</p>
<p>
The
<code class="literal">
table_id
</code>
column value is unique at any
given time, but can be reused if the corresponding object has
been deleted. The same ID can be seen using the
<a class="link" href="mysql-cluster-programs-ndb-show-tables.html" title="25.5.27 ndb_show_tables — Display List of NDB Tables">
<span class="command">
<strong>
ndb_show_tables
</strong>
</span>
</a>
utility.
</p>
<p>
The
<code class="literal">
block_instance
</code>
column shows which LDM
instance this fragment replica belongs to. You can use this to
obtain information about specific threads from the
<a class="link" href="mysql-cluster-ndbinfo-threadblocks.html" title="25.6.17.62 The ndbinfo threadblocks Table">
<code class="literal">
threadblocks
</code>
</a>
table. The first
such instance is always numbered 0.
</p>
<p>
Since there are typically two fragment replicas, and assuming
that this is so, each
<code class="literal">
fragment_num
</code>
value
should appear twice in the table, on two different data nodes
from the same node group.
</p>
<p>
Since
<code class="literal">
NDB
</code>
does not use single-key access for
ordered indexes, the counts for
<code class="literal">
tot_key_reads
</code>
,
<code class="literal">
tot_key_inserts
</code>
,
<code class="literal">
tot_key_updates
</code>
,
<code class="literal">
tot_key_writes
</code>
, and
<code class="literal">
tot_key_deletes
</code>
are not incremented by
ordered index operations.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
When using
<code class="literal">
tot_key_writes
</code>
, you should keep
in mind that a write operation in this context updates the row
if the key exists, and inserts a new row otherwise. (One use
of this is in the
<code class="literal">
NDB
</code>
implementation of the
<a class="link" href="replace.html" title="15.2.12 REPLACE Statement">
<code class="literal">
REPLACE
</code>
</a>
SQL statement.)
</p>
</div>
<p>
The
<code class="literal">
tot_key_refs
</code>
column shows the number of
key operations refused by the LDM. Generally, such a refusal is
due to duplicate keys (inserts),
<span class="errortext">
Key not
found
</span>
errors (updates, deletes, and reads), or the
operation was rejected by an interpreted program used as a
predicate on the row matching the key.
</p>
<p>
The
<code class="literal">
attrinfo
</code>
and
<code class="literal">
keyinfo
</code>
attributes counted by the
<code class="literal">
tot_key_attrinfo_bytes
</code>
and
<code class="literal">
tot_key_keyinfo_bytes
</code>
columns are attributes
of an
<code class="literal">
LQHKEYREQ
</code>
signal (see
<a class="ulink" href="/doc/ndb-internals/en/ndb-internals-ndb-protocol.html" target="_top">
The NDB Communication Protocol
</a>
) used to initiate a
key operation by the LDM. An
<code class="literal">
attrinfo
</code>
typically contains tuple field values (inserts and updates) or
projection specifications (for reads);
<code class="literal">
keyinfo
</code>
contains the primary or unique key
needed to locate a given tuple in this schema object.
</p>
<p>
The value shown by
<code class="literal">
tot_frag_scans
</code>
includes
both full scans (that examine every row) and scans of subsets.
Unique indexes and
<code class="literal">
BLOB
</code>
tables are never
scanned, so this value, like other scan-related counts, is 0 for
fragment replicas of these.
</p>
<p>
<code class="literal">
tot_scan_rows_examined
</code>
may display less than
the total number of rows in a given fragment replica, since
ordered index scans can limited by bounds. In addition, a client
may choose to end a scan before all potentially matching rows
have been examined; this occurs when using an SQL statement
containing a
<code class="literal">
LIMIT
</code>
or
<code class="literal">
EXISTS
</code>
clause, for example.
<code class="literal">
tot_scan_rows_returned
</code>
is always less than or
equal to
<code class="literal">
tot_scan_rows_examined
</code>
.
</p>
<p>
<code class="literal">
tot_scan_bytes_returned
</code>
includes, in the case
of pushed joins, projections returned to the
<a class="ulink" href="/doc/ndb-internals/en/ndb-internals-kernel-blocks-dbspj.html" target="_top">
<code class="literal">
DBSPJ
</code>
</a>
block in the NDB
kernel.
</p>
<p>
<code class="literal">
tot_qd_frag_scans
</code>
can be effected by the
setting for the
<a class="link" href="mysql-cluster-ndbd-definition.html#ndbparam-ndbd-maxparallelscansperfragment">
<code class="literal">
MaxParallelScansPerFragment
</code>
</a>
data node configuration parameter, which limits the number of
scans that may execute concurrently on a single fragment
replica.
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/innodb-compression-tuning.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="innodb-compression-tuning">
</a>
17.9.1.3 Tuning Compression for InnoDB Tables
</h4>
</div>
</div>
</div>
<a class="indexterm" name="idm46045161614704">
</a>
<a class="indexterm" name="idm46045161613216">
</a>
<p>
Most often, the internal optimizations described in
<a class="xref" href="innodb-compression-internals.html#innodb-compression-internals-storage" title="InnoDB Data Storage and Compression">
InnoDB Data Storage and Compression
</a>
ensure
that the system runs well with compressed data. However, because
the efficiency of compression depends on the nature of your
data, you can make decisions that affect the performance of
compressed tables:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
Which tables to compress.
</p>
</li>
<li class="listitem">
<p>
What compressed page size to use.
</p>
</li>
<li class="listitem">
<p>
Whether to adjust the size of the buffer pool based on
run-time performance characteristics, such as the amount of
time the system spends compressing and uncompressing data.
Whether the workload is more like a
<a class="link" href="glossary.html#glos_data_warehouse" title="data warehouse">
data warehouse
</a>
(primarily queries) or an
<a class="link" href="glossary.html#glos_oltp" title="OLTP">
OLTP
</a>
system (mix of queries
and
<a class="link" href="glossary.html#glos_dml" title="DML">
DML
</a>
).
</p>
</li>
<li class="listitem">
<p>
If the system performs DML operations on compressed tables,
and the way the data is distributed leads to expensive
<a class="link" href="glossary.html#glos_compression_failure" title="compression failure">
compression
failures
</a>
at runtime, you might adjust additional
advanced configuration options.
</p>
</li>
</ul>
</div>
<p>
Use the guidelines in this section to help make those
architectural and configuration choices. When you are ready to
conduct long-term testing and put compressed tables into
production, see
<a class="xref" href="innodb-compression-tuning-monitoring.html" title="17.9.1.4 Monitoring InnoDB Table Compression at Runtime">
Section 17.9.1.4, “Monitoring InnoDB Table Compression at Runtime”
</a>
for ways
to verify the effectiveness of those choices under real-world
conditions.
</p>
<h5>
<a name="innodb-compression-tuning-when">
</a>
When to Use Compression
</h5>
<p>
In general, compression works best on tables that include a
reasonable number of character string columns and where the data
is read far more often than it is written. Because there are no
guaranteed ways to predict whether or not compression benefits a
particular situation, always test with a specific
<a class="link" href="glossary.html#glos_workload" title="workload">
workload
</a>
and data set
running on a representative configuration. Consider the
following factors when deciding which tables to compress.
</p>
<h5>
<a name="innodb-compression-tuning-when-data">
</a>
Data Characteristics and Compression
</h5>
<a class="indexterm" name="idm46045161596624">
</a>
<p>
A key determinant of the efficiency of compression in reducing
the size of data files is the nature of the data itself. Recall
that compression works by identifying repeated strings of bytes
in a block of data. Completely randomized data is the worst
case. Typical data often has repeated values, and so compresses
effectively. Character strings often compress well, whether
defined in
<code class="literal">
CHAR
</code>
,
<code class="literal">
VARCHAR
</code>
,
<code class="literal">
TEXT
</code>
or
<code class="literal">
BLOB
</code>
columns. On
the other hand, tables containing mostly binary data (integers
or floating point numbers) or data that is previously compressed
(for example
<acronym class="acronym">
JPEG
</acronym>
or
<acronym class="acronym">
PNG
</acronym>
images) may not generally compress well, significantly or at
all.
</p>
<p>
You choose whether to turn on compression for each InnoDB table.
A table and all of its indexes use the same (compressed)
<a class="link" href="glossary.html#glos_page_size" title="page size">
page size
</a>
. It might be
that the
<a class="link" href="glossary.html#glos_primary_key" title="primary key">
primary key
</a>
(clustered) index, which contains the data for all columns of a
table, compresses more effectively than the secondary indexes.
For those cases where there are long rows, the use of
compression might result in long column values being stored
<span class="quote">
“
<span class="quote">
off-page
</span>
”
</span>
, as discussed in
<a class="xref" href="innodb-row-format.html#innodb-row-format-dynamic" title="DYNAMIC Row Format">
DYNAMIC Row Format
</a>
. Those overflow
pages may compress well. Given these considerations, for many
applications, some tables compress more effectively than others,
and you might find that your workload performs best only with a
subset of tables compressed.
</p>
<p>
To determine whether or not to compress a particular table,
conduct experiments. You can get a rough estimate of how
efficiently your data can be compressed by using a utility that
implements LZ77 compression (such as
<code class="literal">
gzip
</code>
or
WinZip) on a copy of the
<a class="link" href="glossary.html#glos_ibd_file" title=".ibd file">
.ibd
file
</a>
for an uncompressed table. You can expect less
compression from a MySQL compressed table than from file-based
compression tools, because MySQL compresses data in chunks based
on the
<a class="link" href="glossary.html#glos_page_size" title="page size">
page size
</a>
, 16KB by
default. In addition to user data, the page format includes some
internal system data that is not compressed. File-based
compression utilities can examine much larger chunks of data,
and so might find more repeated strings in a huge file than
MySQL can find in an individual page.
</p>
<p>
Another way to test compression on a specific table is to copy
some data from your uncompressed table to a similar, compressed
table (having all the same indexes) in a
<a class="link" href="glossary.html#glos_file_per_table" title="file-per-table">
file-per-table
</a>
tablespace and look at the size of the resulting
<code class="literal">
.ibd
</code>
file. For example:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa69582638"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">USE</span> test<span class="token punctuation">;</span>
<span class="token keyword">SET</span> <span class="token keyword">GLOBAL</span> innodb_file_per_table<span class="token operator">=</span><span class="token number">1</span><span class="token punctuation">;</span>
<span class="token keyword">SET</span> <span class="token keyword">GLOBAL</span> autocommit<span class="token operator">=</span><span class="token number">0</span><span class="token punctuation">;</span>
<span class="token comment" spellcheck="true">-- Create an uncompressed table with a million or two rows.</span>
<span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> big_table <span class="token keyword">AS</span> <span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> information_schema<span class="token punctuation">.</span><span class="token keyword">columns</span><span class="token punctuation">;</span>
<span class="token keyword">INSERT</span> <span class="token keyword">INTO</span> big_table <span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> big_table<span class="token punctuation">;</span>
<span class="token keyword">INSERT</span> <span class="token keyword">INTO</span> big_table <span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> big_table<span class="token punctuation">;</span>
<span class="token keyword">INSERT</span> <span class="token keyword">INTO</span> big_table <span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> big_table<span class="token punctuation">;</span>
<span class="token keyword">INSERT</span> <span class="token keyword">INTO</span> big_table <span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> big_table<span class="token punctuation">;</span>
<span class="token keyword">INSERT</span> <span class="token keyword">INTO</span> big_table <span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> big_table<span class="token punctuation">;</span>
<span class="token keyword">INSERT</span> <span class="token keyword">INTO</span> big_table <span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> big_table<span class="token punctuation">;</span>
<span class="token keyword">INSERT</span> <span class="token keyword">INTO</span> big_table <span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> big_table<span class="token punctuation">;</span>
<span class="token keyword">INSERT</span> <span class="token keyword">INTO</span> big_table <span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> big_table<span class="token punctuation">;</span>
<span class="token keyword">INSERT</span> <span class="token keyword">INTO</span> big_table <span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> big_table<span class="token punctuation">;</span>
<span class="token keyword">INSERT</span> <span class="token keyword">INTO</span> big_table <span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> big_table<span class="token punctuation">;</span>
<span class="token keyword">COMMIT</span><span class="token punctuation">;</span>
<span class="token keyword">ALTER</span> <span class="token keyword">TABLE</span> big_table <span class="token keyword">ADD</span> id <span class="token datatype">int</span> <span class="token keyword">unsigned</span> <span class="token operator">NOT</span> <span class="token boolean">NULL</span> <span class="token keyword">PRIMARY</span> <span class="token keyword">KEY</span> <span class="token keyword">auto_increment</span><span class="token punctuation">;</span>
<span class="token keyword">SHOW</span> <span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> big_table\G
<span class="token keyword">select</span> <span class="token function">count</span><span class="token punctuation">(</span>id<span class="token punctuation">)</span> <span class="token keyword">from</span> big_table<span class="token punctuation">;</span>
<span class="token comment" spellcheck="true">-- Check how much space is needed for the uncompressed table.</span>
\<span class="token operator">!</span> ls <span class="token operator">-</span>l <span class="token keyword">data</span><span class="token operator">/</span>test<span class="token operator">/</span>big_table<span class="token punctuation">.</span>ibd
<span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> key_block_size_4 <span class="token operator">LIKE</span> big_table<span class="token punctuation">;</span>
<span class="token keyword">ALTER</span> <span class="token keyword">TABLE</span> key_block_size_4 <span class="token keyword">key_block_size</span><span class="token operator">=</span><span class="token number">4</span> <span class="token keyword">row_format</span><span class="token operator">=</span><span class="token keyword">compressed</span><span class="token punctuation">;</span>
<span class="token keyword">INSERT</span> <span class="token keyword">INTO</span> key_block_size_4 <span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> big_table<span class="token punctuation">;</span>
<span class="token keyword">commit</span><span class="token punctuation">;</span>
<span class="token comment" spellcheck="true">-- Check how much space is needed for a compressed table</span>
<span class="token comment" spellcheck="true">-- with particular compression settings.</span>
\<span class="token operator">!</span> ls <span class="token operator">-</span>l <span class="token keyword">data</span><span class="token operator">/</span>test<span class="token operator">/</span>key_block_size_4<span class="token punctuation">.</span>ibd</code></pre>
</div>
<p>
This experiment produced the following numbers, which of course
could vary considerably depending on your table structure and
data:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-terminal"><div class="docs-select-all right" id="sa35342686"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-terminal"><span class="token property">-rw-rw----</span> 1 cirrus staff 310378496 Jan 9 13<span class="token punctuation">:</span>44 data/test/big_table<span class="token punctuation">.</span>ibd
<span class="token property">-rw-rw----</span> 1 cirrus staff 83886080 Jan 9 15<span class="token punctuation">:</span>10 data/test/key_block_size_4<span class="token punctuation">.</span>ibd</code></pre>
</div>
<p>
To see whether compression is efficient for your particular
<a class="link" href="glossary.html#glos_workload" title="workload">
workload
</a>
:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
For simple tests, use a MySQL instance with no other
compressed tables and run queries against the Information
Schema
<a class="link" href="information-schema-innodb-cmp-table.html" title="28.4.6 The INFORMATION_SCHEMA INNODB_CMP and INNODB_CMP_RESET Tables">
<code class="literal">
INNODB_CMP
</code>
</a>
table.
</p>
</li>
<li class="listitem">
<p>
For more elaborate tests involving workloads with multiple
compressed tables, run queries against the Information
Schema
<a class="link" href="information-schema-innodb-cmp-per-index-table.html" title="28.4.8 The INFORMATION_SCHEMA INNODB_CMP_PER_INDEX and INNODB_CMP_PER_INDEX_RESET Tables">
<code class="literal">
INNODB_CMP_PER_INDEX
</code>
</a>
table. Because the statistics in the
<code class="literal">
INNODB_CMP_PER_INDEX
</code>
table are expensive
to collect, you must enable the configuration option
<a class="link" href="innodb-parameters.html#sysvar_innodb_cmp_per_index_enabled">
<code class="literal">
innodb_cmp_per_index_enabled
</code>
</a>
before querying that table, and you might restrict such
testing to a development server or a non-critical replica
server.
</p>
</li>
<li class="listitem">
<p>
Run some typical SQL statements against the compressed table
you are testing.
</p>
</li>
<li class="listitem">
<p>
Examine the ratio of successful compression operations to
overall compression operations by querying
<a class="link" href="information-schema-innodb-cmp-table.html" title="28.4.6 The INFORMATION_SCHEMA INNODB_CMP and INNODB_CMP_RESET Tables">
<code class="literal">
INFORMATION_SCHEMA.INNODB_CMP
</code>
</a>
or
<a class="link" href="information-schema-innodb-cmp-per-index-table.html" title="28.4.8 The INFORMATION_SCHEMA INNODB_CMP_PER_INDEX and INNODB_CMP_PER_INDEX_RESET Tables">
<code class="literal">
INFORMATION_SCHEMA.INNODB_CMP_PER_INDEX
</code>
</a>
,
and comparing
<code class="literal">
COMPRESS_OPS
</code>
to
<code class="literal">
COMPRESS_OPS_OK
</code>
.
</p>
</li>
<li class="listitem">
<p>
If a high percentage of compression operations complete
successfully, the table might be a good candidate for
compression.
</p>
</li>
<li class="listitem">
<p>
If you get a high proportion of
<a class="link" href="glossary.html#glos_compression_failure" title="compression failure">
compression
failures
</a>
, you can adjust
<a class="link" href="innodb-parameters.html#sysvar_innodb_compression_level">
<code class="literal">
innodb_compression_level
</code>
</a>
,
<a class="link" href="innodb-parameters.html#sysvar_innodb_compression_failure_threshold_pct">
<code class="literal">
innodb_compression_failure_threshold_pct
</code>
</a>
,
and
<a class="link" href="innodb-parameters.html#sysvar_innodb_compression_pad_pct_max">
<code class="literal">
innodb_compression_pad_pct_max
</code>
</a>
options as described in
<a class="xref" href="innodb-performance-compression-oltp.html" title="17.9.1.6 Compression for OLTP Workloads">
Section 17.9.1.6, “Compression for OLTP Workloads”
</a>
, and
try further tests.
</p>
</li>
</ul>
</div>
<h5>
<a name="innodb-compression-application">
</a>
Database Compression versus Application Compression
</h5>
<a class="indexterm" name="idm46045161553472">
</a>
<p>
Decide whether to compress data in your application or in the
table; do not use both types of compression for the same data.
When you compress the data in the application and store the
results in a compressed table, extra space savings are extremely
unlikely, and the double compression just wastes CPU cycles.
</p>
<h5>
<a name="innodb-compression-in-database">
</a>
Compressing in the Database
</h5>
<p>
When enabled, MySQL table compression is automatic and applies
to all columns and index values. The columns can still be tested
with operators such as
<code class="literal">
LIKE
</code>
, and sort
operations can still use indexes even when the index values are
compressed. Because indexes are often a significant fraction of
the total size of a database, compression could result in
significant savings in storage, I/O or processor time. The
compression and decompression operations happen on the database
server, which likely is a powerful system that is sized to
handle the expected load.
</p>
<h5>
<a name="innodb-compression-in-application">
</a>
Compressing in the Application
</h5>
<p>
If you compress data such as text in your application, before it
is inserted into the database, You might save overhead for data
that does not compress well by compressing some columns and not
others. This approach uses CPU cycles for compression and
uncompression on the client machine rather than the database
server, which might be appropriate for a distributed application
with many clients, or where the client machine has spare CPU
cycles.
</p>
<h5>
<a name="innodb-compression-hybrid">
</a>
Hybrid Approach
</h5>
<p>
Of course, it is possible to combine these approaches. For some
applications, it may be appropriate to use some compressed
tables and some uncompressed tables. It may be best to
externally compress some data (and store it in uncompressed
tables) and allow MySQL to compress (some of) the other tables
in the application. As always, up-front design and real-life
testing are valuable in reaching the right decision.
</p>
<h5>
<a name="innodb-compression-tuning-when-workload">
</a>
Workload Characteristics and Compression
</h5>
<a class="indexterm" name="idm46045161542752">
</a>
<p>
In addition to choosing which tables to compress (and the page
size), the workload is another key determinant of performance.
If the application is dominated by reads, rather than updates,
fewer pages need to be reorganized and recompressed after the
index page runs out of room for the per-page
<span class="quote">
“
<span class="quote">
modification
log
</span>
”
</span>
that MySQL maintains for compressed data. If the
updates predominantly change non-indexed columns or those
containing
<code class="literal">
BLOB
</code>
s or large strings that happen
to be stored
<span class="quote">
“
<span class="quote">
off-page
</span>
”
</span>
, the overhead of
compression may be acceptable. If the only changes to a table
are
<code class="literal">
INSERT
</code>
s that use a monotonically
increasing primary key, and there are few secondary indexes,
there is little need to reorganize and recompress index pages.
Since MySQL can
<span class="quote">
“
<span class="quote">
delete-mark
</span>
”
</span>
and delete rows on
compressed pages
<span class="quote">
“
<span class="quote">
in place
</span>
”
</span>
by modifying
uncompressed data,
<code class="literal">
DELETE
</code>
operations on a
table are relatively efficient.
</p>
<p>
For some environments, the time it takes to load data can be as
important as run-time retrieval. Especially in data warehouse
environments, many tables may be read-only or read-mostly. In
those cases, it might or might not be acceptable to pay the
price of compression in terms of increased load time, unless the
resulting savings in fewer disk reads or in storage cost is
significant.
</p>
<p>
Fundamentally, compression works best when the CPU time is
available for compressing and uncompressing data. Thus, if your
workload is I/O bound, rather than CPU-bound, you might find
that compression can improve overall performance. When you test
your application performance with different compression
configurations, test on a platform similar to the planned
configuration of the production system.
</p>
<h5>
<a name="innodb-compression-tuning-when-config">
</a>
Configuration Characteristics and Compression
</h5>
<a class="indexterm" name="idm46045161533056">
</a>
<p>
Reading and writing database
<a class="link" href="glossary.html#glos_page" title="page">
pages
</a>
from and to disk is the
slowest aspect of system performance. Compression attempts to
reduce I/O by using CPU time to compress and uncompress data,
and is most effective when I/O is a relatively scarce resource
compared to processor cycles.
</p>
<p>
This is often especially the case when running in a multi-user
environment with fast, multi-core CPUs. When a page of a
compressed table is in memory, MySQL often uses additional
memory, typically 16KB, in the
<a class="link" href="glossary.html#glos_buffer_pool" title="buffer pool">
buffer pool
</a>
for an
uncompressed copy of the page. The adaptive LRU algorithm
attempts to balance the use of memory between compressed and
uncompressed pages to take into account whether the workload is
running in an I/O-bound or CPU-bound manner. Still, a
configuration with more memory dedicated to the buffer pool
tends to run better when using compressed tables than a
configuration where memory is highly constrained.
</p>
<h5>
<a name="innodb-compression-tuning-when-size">
</a>
Choosing the Compressed Page Size
</h5>
<a class="indexterm" name="idm46045161526864">
</a>
<a class="indexterm" name="idm46045161525376">
</a>
<a class="indexterm" name="idm46045161523888">
</a>
<a class="indexterm" name="idm46045161522400">
</a>
<p>
The optimal setting of the compressed page size depends on the
type and distribution of data that the table and its indexes
contain. The compressed page size should always be bigger than
the maximum record size, or operations may fail as noted in
<a class="xref" href="innodb-compression-internals.html#innodb-compression-internals-storage-btree" title="Compression of B-Tree Pages">
Compression of B-Tree Pages
</a>
.
</p>
<p>
Setting the compressed page size too large wastes some space,
but the pages do not have to be compressed as often. If the
compressed page size is set too small, inserts or updates may
require time-consuming recompression, and the
<a class="link" href="glossary.html#glos_b_tree" title="B-tree">
B-tree
</a>
nodes may have to be
split more frequently, leading to bigger data files and less
efficient indexing.
</p>
<p>
Typically, you set the compressed page size to 8K or 4K bytes.
Given that the maximum row size for an InnoDB table is around
8K,
<code class="literal">
KEY_BLOCK_SIZE=8
</code>
is usually a safe
choice.
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/group-replication-compatibility-upgrade.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="group-replication-compatibility-upgrade">
</a>
20.8.1.1 Member Versions During Upgrades
</h4>
</div>
</div>
</div>
<p>
During an online upgrade procedure, if the group is in
single-primary mode, all the servers that are not currently
offline for upgrading function as they did before. The group
elects a new primary whenever necessary, following the election
policies described in
<a class="xref" href="group-replication-single-primary-mode.html" title="20.1.3.1 Single-Primary Mode">
Section 20.1.3.1, “Single-Primary Mode”
</a>
. Note
that if you require the primary to remain the same throughout
(except when it is being upgraded itself), you must first
upgrade all of the secondaries to a version higher than or equal
to the target primary member version, then upgrade the primary
last. The primary cannot remain as the primary unless it is
running the lowest MySQL Server version in the group. After the
primary has been upgraded, you can use the
<a class="link" href="group-replication-functions-for-new-primary.html#function_group-replication-set-as-primary">
<code class="literal">
group_replication_set_as_primary()
</code>
</a>
function to reappoint it as the primary.
</p>
<p>
If the group is in multi-primary mode, fewer online members are
available to perform writes during the upgrade procedure,
because upgraded members join in read-only mode after their
upgrade. When all members have been upgraded to the same
release, they all change back to read/write mode automatically.
</p>
<p>
To deal with a problem situation, for example if you have to
roll back an upgrade to a previous major version or add extra
capacity to a group in an emergency, it is possible to allow a
member to join an online group from a version that otherwise
couldn't. The deprecated Group Replication system variable
<a class="link" href="group-replication-system-variables.html#sysvar_group_replication_allow_local_lower_version_join">
<code class="literal">
group_replication_allow_local_lower_version_join
</code>
</a>
can be used in such situations to override the normal
compatibility policies.
</p>
<div class="important" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Important
</div>
<p>
Setting
<a class="link" href="group-replication-system-variables.html#sysvar_group_replication_allow_local_lower_version_join">
<code class="literal">
group_replication_allow_local_lower_version_join
</code>
</a>
to
<code class="literal">
ON
</code>
does
<span class="emphasis">
<em>
not
</em>
</span>
make
the new member compatible with the group; doing this allows it
to join the group without any safeguards against incompatible
behaviors by the existing members. This must therefore only be
used carefully in specific situations, and you must take
additional precautions to avoid the new member failing due to
normal group activity. See the description of this variable
for more information.
</p>
</div>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
<code class="literal">
group_replication_allow_local_lower_version_join
</code>
is deprecated and subject to removal in a future version of
MySQL. Setting it generates a
<a class="ulink" href="/doc/mysql-errors/8.4/en/server-error-reference.html#error_er_warn_deprecated_syntax_no_replacement" target="_top">
<code class="literal">
ER_WARN_DEPRECATED_SYNTAX_NO_REPLACEMENT
</code>
</a>
warning.
</p>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/blackhole-storage-engine.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h2 class="title">
<a name="blackhole-storage-engine">
</a>
18.6 The BLACKHOLE Storage Engine
</h2>
</div>
</div>
</div>
<a class="indexterm" name="idm46045147569184">
</a>
<a class="indexterm" name="idm46045147568096">
</a>
<p>
The
<code class="literal">
BLACKHOLE
</code>
storage engine acts as a
<span class="quote">
“
<span class="quote">
black hole
</span>
”
</span>
that accepts data but throws it away and
does not store it. Retrievals always return an empty result:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa93063082"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> test<span class="token punctuation">(</span>i <span class="token datatype">INT</span><span class="token punctuation">,</span> c <span class="token datatype">CHAR</span><span class="token punctuation">(</span><span class="token number">10</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token keyword">ENGINE</span> <span class="token operator">=</span> BLACKHOLE<span class="token punctuation">;</span>
<span class="token output">Query OK, 0 rows affected (0.03 sec)</span>
<span class="token prompt">mysql></span> <span class="token keyword">INSERT</span> <span class="token keyword">INTO</span> test <span class="token keyword">VALUES</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span><span class="token string">'record one'</span><span class="token punctuation">)</span><span class="token punctuation">,</span><span class="token punctuation">(</span><span class="token number">2</span><span class="token punctuation">,</span><span class="token string">'record two'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token output">Query OK, 2 rows affected (0.00 sec)</span>
<span class="token output">Records: 2 Duplicates: 0 Warnings: 0</span>
<span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> test<span class="token punctuation">;</span>
<span class="token output">Empty set (0.00 sec)</span></code></pre>
</div>
<p>
To enable the
<code class="literal">
BLACKHOLE
</code>
storage engine if you
build MySQL from source, invoke
<span class="command">
<strong>
CMake
</strong>
</span>
with the
<a class="link" href="source-configuration-options.html#option_cmake_storage_engine_options" title="Storage Engine Options">
<code class="option">
-DWITH_BLACKHOLE_STORAGE_ENGINE
</code>
</a>
option.
</p>
<p>
To examine the source for the
<code class="literal">
BLACKHOLE
</code>
engine,
look in the
<code class="filename">
sql
</code>
directory of a MySQL source
distribution.
</p>
<p>
When you create a
<code class="literal">
BLACKHOLE
</code>
table, the server
creates the table definition in the global data dictionary. There
are no files associated with the table.
</p>
<p>
The
<code class="literal">
BLACKHOLE
</code>
storage engine supports all kinds
of indexes. That is, you can include index declarations in the table
definition.
</p>
<p>
The maximum key length is 3072 bytes.
</p>
<p>
The
<code class="literal">
BLACKHOLE
</code>
storage engine does not support
partitioning.
</p>
<p>
You can check whether the
<code class="literal">
BLACKHOLE
</code>
storage
engine is available with the
<a class="link" href="show-engines.html" title="15.7.7.17 SHOW ENGINES Statement">
<code class="literal">
SHOW
ENGINES
</code>
</a>
statement.
</p>
<p>
Inserts into a
<code class="literal">
BLACKHOLE
</code>
table do not store any
data, but if statement based binary logging is enabled, the SQL
statements are logged and replicated to replica servers. This can be
useful as a repeater or filter mechanism.
</p>
<p>
Suppose that your application requires replica-side filtering rules,
but transferring all binary log data to the replica first results in
too much traffic. In such a case, it is possible to set up on the
replication source server a
<span class="quote">
“
<span class="quote">
dummy
</span>
”
</span>
replica process
whose default storage engine is
<code class="literal">
BLACKHOLE
</code>
,
depicted as follows:
</p>
<div class="figure">
<a name="idm46045147546960">
</a>
<p class="title">
<b>
Figure 18.1 Replication using BLACKHOLE for Filtering
</b>
</p>
<div class="figure-contents">
<div class="mediaobject">
<img alt="The replication source server uses a source mysqld process and a dummy mysqld process. On the replica, the mysqld process replicates from the dummy mysqld process." src="images/blackhole-1.png" style="width: 100%; max-width: 575px;"/>
</div>
</div>
</div>
<br class="figure-break"/>
<p>
The source writes to its binary log. The
<span class="quote">
“
<span class="quote">
dummy
</span>
”
</span>
<a class="link" href="mysqld.html" title="6.3.1 mysqld — The MySQL Server">
<span class="command">
<strong>
mysqld
</strong>
</span>
</a>
process acts as a replica, applying the
desired combination of
<code class="literal">
replicate-do-*
</code>
and
<code class="literal">
replicate-ignore-*
</code>
rules, and writes a new,
filtered binary log of its own. (See
<a class="xref" href="replication-options.html" title="19.1.6 Replication and Binary Logging Options and Variables">
Section 19.1.6, “Replication and Binary Logging Options and Variables”
</a>
.) This filtered log is
provided to the replica.
</p>
<p>
The dummy process does not actually store any data, so there is
little processing overhead incurred by running the additional
<a class="link" href="mysqld.html" title="6.3.1 mysqld — The MySQL Server">
<span class="command">
<strong>
mysqld
</strong>
</span>
</a>
process on the replication source server.
This type of setup can be repeated with additional replicas.
</p>
<p>
<a class="link" href="insert.html" title="15.2.7 INSERT Statement">
<code class="literal">
INSERT
</code>
</a>
triggers for
<code class="literal">
BLACKHOLE
</code>
tables work as expected. However,
because the
<code class="literal">
BLACKHOLE
</code>
table does not actually
store any data,
<a class="link" href="update.html" title="15.2.17 UPDATE Statement">
<code class="literal">
UPDATE
</code>
</a>
and
<a class="link" href="delete.html" title="15.2.2 DELETE Statement">
<code class="literal">
DELETE
</code>
</a>
triggers are not activated:
The
<code class="literal">
FOR EACH ROW
</code>
clause in the trigger definition
does not apply because there are no rows.
</p>
<p>
Other possible uses for the
<code class="literal">
BLACKHOLE
</code>
storage
engine include:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
Verification of dump file syntax.
</p>
</li>
<li class="listitem">
<p>
Measurement of the overhead from binary logging, by comparing
performance using
<code class="literal">
BLACKHOLE
</code>
with and without
binary logging enabled.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
BLACKHOLE
</code>
is essentially a
<span class="quote">
“
<span class="quote">
no-op
</span>
”
</span>
storage engine, so it could be used for
finding performance bottlenecks not related to the storage
engine itself.
</p>
</li>
</ul>
</div>
<p>
The
<code class="literal">
BLACKHOLE
</code>
engine is transaction-aware, in the
sense that committed transactions are written to the binary log and
rolled-back transactions are not.
</p>
<p>
<span class="bold">
<strong>
Blackhole Engine and Auto Increment
Columns
</strong>
</span>
</p>
<p>
The
<code class="literal">
BLACKHOLE
</code>
engine is a no-op engine. Any
operations performed on a table using
<code class="literal">
BLACKHOLE
</code>
have no effect. This should be borne in mind when considering the
behavior of primary key columns that auto increment. The engine does
not automatically increment field values, and does not retain auto
increment field state. This has important implications in
replication.
</p>
<p>
Consider the following replication scenario where all three of the
following conditions apply:
</p>
<div class="orderedlist">
<ol class="orderedlist" type="1">
<li class="listitem">
<p>
On a source server there is a blackhole table with an auto
increment field that is a primary key.
</p>
</li>
<li class="listitem">
<p>
On a replica the same table exists but using the MyISAM engine.
</p>
</li>
<li class="listitem">
<p>
Inserts are performed into the source's table without explicitly
setting the auto increment value in the
<code class="literal">
INSERT
</code>
statement itself or through using a
<code class="literal">
SET INSERT_ID
</code>
statement.
</p>
</li>
</ol>
</div>
<p>
In this scenario replication fails with a duplicate entry error on
the primary key column.
</p>
<p>
In statement based replication, the value of
<code class="literal">
INSERT_ID
</code>
in the context event is always the
same. Replication therefore fails due to trying insert a row with a
duplicate value for a primary key column.
</p>
<p>
In row based replication, the value that the engine returns for the
row always be the same for each insert. This results in the replica
attempting to replay two insert log entries using the same value for
the primary key column, and so replication fails.
</p>
<p>
<span class="bold">
<strong>
Column Filtering
</strong>
</span>
</p>
<p>
When using row-based replication,
(
<a class="link" href="replication-options-binary-log.html#sysvar_binlog_format">
<code class="literal">
binlog_format=ROW
</code>
</a>
), a replica
where the last columns are missing from a table is supported, as
described in the section
<a class="xref" href="replication-features-differing-tables.html" title="19.5.1.9 Replication with Differing Table Definitions on Source and Replica">
Section 19.5.1.9, “Replication with Differing Table Definitions on Source and Replica”
</a>
.
</p>
<p>
This filtering works on the replica side, that is, the columns are
copied to the replica before they are filtered out. There are at
least two cases where it is not desirable to copy the columns to the
replica:
</p>
<div class="orderedlist">
<ol class="orderedlist" type="1">
<li class="listitem">
<p>
If the data is confidential, so the replica server should not
have access to it.
</p>
</li>
<li class="listitem">
<p>
If the source has many replicas, filtering before sending to the
replicas may reduce network traffic.
</p>
</li>
</ol>
</div>
<p>
Source column filtering can be achieved using the
<code class="literal">
BLACKHOLE
</code>
engine. This is carried out in a way
similar to how source table filtering is achieved - by using the
<code class="literal">
BLACKHOLE
</code>
engine and the
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-do-table">
<code class="option">
--replicate-do-table
</code>
</a>
or
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-ignore-table">
<code class="option">
--replicate-ignore-table
</code>
</a>
option.
</p>
<p>
The setup for the source is:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa28874521"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> t1 <span class="token punctuation">(</span>public_col_1<span class="token punctuation">,</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">,</span> public_col_N<span class="token punctuation">,</span>
secret_col_1<span class="token punctuation">,</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">,</span> secret_col_M<span class="token punctuation">)</span> <span class="token keyword">ENGINE</span><span class="token operator">=</span>MyISAM<span class="token punctuation">;</span></code></pre>
</div>
<p>
The setup for the trusted replica is:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa8778354"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> t1 <span class="token punctuation">(</span>public_col_1<span class="token punctuation">,</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">,</span> public_col_N<span class="token punctuation">)</span> <span class="token keyword">ENGINE</span><span class="token operator">=</span>BLACKHOLE<span class="token punctuation">;</span></code></pre>
</div>
<p>
The setup for the untrusted replica is:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa90139625"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> t1 <span class="token punctuation">(</span>public_col_1<span class="token punctuation">,</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">,</span> public_col_N<span class="token punctuation">)</span> <span class="token keyword">ENGINE</span><span class="token operator">=</span>MyISAM<span class="token punctuation">;</span></code></pre>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/install-component.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="install-component">
</a>
15.7.4.3 INSTALL COMPONENT Statement
</h4>
</div>
</div>
</div>
<a class="indexterm" name="idm46045171801904">
</a>
<a class="indexterm" name="idm46045171800816">
</a>
<a class="indexterm" name="idm46045171799744">
</a>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa64657889"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">INSTALL</span> <span class="token keyword">COMPONENT</span> <em class="replaceable">component_name</em> <span class="token punctuation">[</span><span class="token punctuation">,</span> <em class="replaceable">component_name</em> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token punctuation">[</span><span class="token keyword">SET</span> <em class="replaceable">variable</em> <span class="token operator">=</span> <em class="replaceable">expr</em> <span class="token punctuation">[</span><span class="token punctuation">,</span> <em class="replaceable">variable</em> <span class="token operator">=</span> <em class="replaceable">expr</em><span class="token punctuation">]</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">]</span>
<em class="replaceable">variable</em>: {
{<span class="token keyword">GLOBAL</span> <span class="token operator">|</span> <span class="token variable">@@GLOBAL.</span>} <span class="token punctuation">[</span><em class="replaceable">component_prefix</em><span class="token punctuation">.</span><span class="token punctuation">]</span><em class="replaceable">system_var_name</em>
<span class="token operator">|</span> {<span class="token keyword">PERSIST</span> <span class="token operator">|</span> <span class="token variable">@@PERSIST.</span>} <span class="token punctuation">[</span><em class="replaceable">component_prefix</em><span class="token punctuation">.</span><span class="token punctuation">]</span><em class="replaceable">system_var_name</em>
}</code></pre>
</div>
<p>
This statement installs one or more components, which become
active immediately. A component provides services that are
available to the server and other components; see
<a class="xref" href="components.html" title="7.5 MySQL Components">
Section 7.5, “MySQL Components”
</a>
.
<a class="link" href="install-component.html" title="15.7.4.3 INSTALL COMPONENT Statement">
<code class="literal">
INSTALL
COMPONENT
</code>
</a>
requires the
<a class="link" href="privileges-provided.html#priv_insert">
<code class="literal">
INSERT
</code>
</a>
privilege for the
<code class="literal">
mysql.component
</code>
system table because it adds
a row to that table to register the component.
</p>
<p>
Example:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa95697724"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">INSTALL</span> <span class="token keyword">COMPONENT</span> <span class="token string">'file://component1'</span><span class="token punctuation">,</span> <span class="token string">'file://component2'</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
A component is named using a URN that begins with
<code class="literal">
file://
</code>
and indicates the base name of the
library file that implements the component, located in the
directory named by the
<a class="link" href="server-system-variables.html#sysvar_plugin_dir">
<code class="literal">
plugin_dir
</code>
</a>
system variable.
Component names do not include any platform-dependent file name
suffix such as
<code class="filename">
.so
</code>
or
<code class="filename">
.dll
</code>
. (These naming details are subject to
change because component name interpretation is itself performed
by a service and the component infrastructure makes it possible
to replace the default service implementation with alternative
implementations.)
</p>
<p>
<a class="link" href="install-component.html" title="15.7.4.3 INSTALL COMPONENT Statement">
<code class="literal">
INSTALL COMPONENT
</code>
</a>
permits setting
the values of component system variables when you install one or
more components. The
<code class="literal">
SET
</code>
clause enables you
to specify variable values precisely when they are needed,
without the inconvenience or limitations associated with other
forms of assignment. Specifically, you can also set component
variables with these alternatives:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
At server startup using options on the command line or in an
option file, but doing so involves a server restart. The
values do not take effect until you install the component.
You can specify an invalid variable name for a component on
the command line without triggering an error.
</p>
</li>
<li class="listitem">
<p>
Dynamically while the server is running by means of the
<a class="link" href="set.html" title="13.3.6 The SET Type">
<code class="literal">
SET
</code>
</a>
statement, which enables
you to modify operation of the server without having to stop
and restart it. Setting a read-only variable is not
permitted.
</p>
</li>
</ul>
</div>
<p>
The optional
<code class="literal">
SET
</code>
clause applies a value, or
values, only to the component specified in the
<a class="link" href="install-component.html" title="15.7.4.3 INSTALL COMPONENT Statement">
<code class="literal">
INSTALL COMPONENT
</code>
</a>
statement,
rather than to all subsequent installations of that component.
<code class="literal">
SET GLOBAL|PERSIST
</code>
works for all types of
variables, including read-only variables, without having to
restart the server. A component system variable that you set
using
<a class="link" href="install-component.html" title="15.7.4.3 INSTALL COMPONENT Statement">
<code class="literal">
INSTALL COMPONENT
</code>
</a>
takes
precedence over any conflicting value coming from the command
line or an option file.
</p>
<p>
Example:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa29517664"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">INSTALL</span> <span class="token keyword">COMPONENT</span> <span class="token string">'file://component1'</span><span class="token punctuation">,</span> <span class="token string">'file://component2'</span>
<span class="token keyword">SET</span> <span class="token keyword">GLOBAL</span> component1<span class="token punctuation">.</span>var1 <span class="token operator">=</span> <span class="token number">12</span> <span class="token operator">+</span> <span class="token number">3</span><span class="token punctuation">,</span> <span class="token keyword">PERSIST</span> component2<span class="token punctuation">.</span>var2 <span class="token operator">=</span> <span class="token string">'strings'</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
Omitting
<code class="literal">
PERSIST
</code>
or
<code class="literal">
GLOBAL
</code>
is equivalent to specifying
<code class="literal">
GLOBAL
</code>
.
</p>
<p>
Specifying
<code class="literal">
PERSIST
</code>
for any variable in
<code class="literal">
SET
</code>
silently executes
<code class="literal">
SET
PERSIST_ONLY
</code>
immediately after
<a class="link" href="install-component.html" title="15.7.4.3 INSTALL COMPONENT Statement">
<code class="literal">
INSTALL COMPONENT
</code>
</a>
loads the
components, but before updating the
<code class="literal">
mysql.component
</code>
table. If
<code class="literal">
SET
PERSIST_ONLY
</code>
fails, then the server unloads all of the
previously loaded new components without persisting anything to
<code class="literal">
mysql.component
</code>
.
</p>
<p>
The
<code class="literal">
SET
</code>
clause accepts only valid variable
names of the component being installed and emits an error
message for all invalid names. Subqueries, stored functions, and
aggregate functions are not permitted as part of the value
expression. If you install a single component, it is not
necessary to prefix the variable name with the component name.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
While specifying a variable value using the
<code class="literal">
SET
</code>
clause is similar to that of the
command line—it is available immediately at variable
registration—there is a distinct difference in how the
<code class="literal">
SET
</code>
clause handles
<span class="emphasis">
<em>
invalid
numerical
</em>
</span>
values for boolean variables. For
example, if you set a boolean variable to 11
(
<code class="literal">
component1.boolvar = 11
</code>
), you see the
following behavior:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<code class="literal">
SET
</code>
clause yields true
</p>
</li>
<li class="listitem">
<p>
Command line yields false (11 is neither ON nor 1)
</p>
</li>
</ul>
</div>
</div>
<p>
If any error occurs, the statement fails and has no effect. For
example, this happens if a component name is erroneous, a named
component does not exist or is already installed, or component
initialization fails.
</p>
<p>
A loader service handles component loading, which includes
adding installed components to the
<code class="literal">
mysql.component
</code>
system table that serves as a
registry. For subsequent server restarts, any components listed
in
<code class="literal">
mysql.component
</code>
are loaded by the loader
service during the startup sequence. This occurs even if the
server is started with the
<a class="link" href="server-options.html#option_mysqld_skip-grant-tables">
<code class="option">
--skip-grant-tables
</code>
</a>
option.
</p>
<p>
If a component depends on services not present in the registry
and you attempt to install the component without also installing
the component or components that provide the services on which
it depends, an error occurs:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-none"><div class="docs-select-all right" id="sa78619415"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-none">ERROR 3527 (HY000): Cannot satisfy dependency for service 'component_a'
required by component 'component_b'.</code></pre>
</div>
<p>
To avoid this problem, either install all components in the same
statement, or install the dependent component after installing
any components on which it depends.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
For keyring components, do not use
<a class="link" href="install-component.html" title="15.7.4.3 INSTALL COMPONENT Statement">
<code class="literal">
INSTALL COMPONENT
</code>
</a>
. Instead,
configure keyring component loading using a manifest file. See
<a class="xref" href="keyring-component-installation.html" title="8.4.4.2 Keyring Component Installation">
Section 8.4.4.2, “Keyring Component Installation”
</a>
.
</p>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/faqs-storage-engines.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h2 class="title">
<a name="faqs-storage-engines">
</a>
A.2 MySQL 8.4 FAQ: Storage Engines
</h2>
</div>
</div>
</div>
<div class="qandaset">
<a name="idm46045056447408">
</a>
<dl>
<dt>
A.2.1.
<a href="faqs-storage-engines.html#faq-mysql-what-storage-engines">
Where can I obtain complete documentation for MySQL storage
engines?
</a>
</dt>
<dt>
A.2.2.
<a href="faqs-storage-engines.html#faq-mysql-have-new-storage-engines">
Are there any new storage engines in MySQL 8.4?
</a>
</dt>
<dt>
A.2.3.
<a href="faqs-storage-engines.html#faq-mysql-removed-storage-engines">
Have any storage engines been removed in MySQL 8.4?
</a>
</dt>
<dt>
A.2.4.
<a href="faqs-storage-engines.html#faq-mysql-disabling-storage-engines">
Can I prevent the use of a particular storage engine?
</a>
</dt>
<dt>
A.2.5.
<a href="faqs-storage-engines.html#faq-mysql-innodb-backup-recovery-advantage">
Is there an advantage to using the InnoDB
storage engine exclusively, as opposed to a combination of
InnoDB and non-InnoDB
storage engines?
</a>
</dt>
<dt>
A.2.6.
<a href="faqs-storage-engines.html#faq-mysql-what-archive-engine">
What are the unique benefits of the ARCHIVE
storage engine?
</a>
</dt>
</dl>
<table border="0" style="width: 100%;">
<colgroup>
<col align="left" width="1%"/>
<col/>
</colgroup>
<tbody>
<tr class="question">
<td align="left" valign="top">
<a name="faq-mysql-what-storage-engines">
</a>
<a name="idm46045056446592">
</a>
<p>
<b>
A.2.1.
</b>
</p>
</td>
<td align="left" valign="top">
<p>
Where can I obtain complete documentation for MySQL storage
engines?
</p>
</td>
</tr>
<tr class="answer">
<td align="left" valign="top">
</td>
<td align="left" valign="top">
<p>
See
<a class="xref" href="storage-engines.html" title="Chapter 18 Alternative Storage Engines">
Chapter 18,
<i>
Alternative Storage Engines
</i>
</a>
. That chapter contains
information about all MySQL storage engines except for the
<a class="link" href="innodb-storage-engine.html" title="Chapter 17 The InnoDB Storage Engine">
<code class="literal">
InnoDB
</code>
</a>
storage engine and the
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDB
</code>
</a>
storage engine (used for MySQL
Cluster).
<a class="link" href="innodb-storage-engine.html" title="Chapter 17 The InnoDB Storage Engine">
<code class="literal">
InnoDB
</code>
</a>
is covered in
<a class="xref" href="innodb-storage-engine.html" title="Chapter 17 The InnoDB Storage Engine">
Chapter 17,
<i>
The InnoDB Storage Engine
</i>
</a>
.
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDB
</code>
</a>
is covered in
<a class="xref" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
Chapter 25,
<i>
MySQL NDB Cluster 8.4
</i>
</a>
.
</p>
</td>
</tr>
<tr class="question">
<td align="left" valign="top">
<a name="faq-mysql-have-new-storage-engines">
</a>
<a name="idm46045056437616">
</a>
<p>
<b>
A.2.2.
</b>
</p>
</td>
<td align="left" valign="top">
<p>
Are there any new storage engines in MySQL 8.4?
</p>
</td>
</tr>
<tr class="answer">
<td align="left" valign="top">
</td>
<td align="left" valign="top">
<p>
No.
<code class="literal">
InnoDB
</code>
is the default storage engine for
new tables. See
<a class="xref" href="innodb-introduction.html" title="17.1 Introduction to InnoDB">
Section 17.1, “Introduction to InnoDB”
</a>
for
details.
</p>
</td>
</tr>
<tr class="question">
<td align="left" valign="top">
<a name="faq-mysql-removed-storage-engines">
</a>
<a name="idm46045056434096">
</a>
<p>
<b>
A.2.3.
</b>
</p>
</td>
<td align="left" valign="top">
<p>
Have any storage engines been removed in MySQL 8.4?
</p>
</td>
</tr>
<tr class="answer">
<td align="left" valign="top">
</td>
<td align="left" valign="top">
<p>
No.
</p>
</td>
</tr>
<tr class="question">
<td align="left" valign="top">
<a name="faq-mysql-disabling-storage-engines">
</a>
<a name="idm46045056432208">
</a>
<p>
<b>
A.2.4.
</b>
</p>
</td>
<td align="left" valign="top">
<p>
Can I prevent the use of a particular storage engine?
</p>
</td>
</tr>
<tr class="answer">
<td align="left" valign="top">
</td>
<td align="left" valign="top">
<p>
Yes. The
<a class="link" href="server-system-variables.html#sysvar_disabled_storage_engines">
<code class="literal">
disabled_storage_engines
</code>
</a>
configuration option defines which storage engines cannot be
used to create tables or tablespaces. By default,
<a class="link" href="server-system-variables.html#sysvar_disabled_storage_engines">
<code class="literal">
disabled_storage_engines
</code>
</a>
is
empty (no engines disabled), but it can be set to a
comma-separated list of one or more engines.
</p>
</td>
</tr>
<tr class="question">
<td align="left" valign="top">
<a name="faq-mysql-innodb-backup-recovery-advantage">
</a>
<a name="idm46045056427312">
</a>
<p>
<b>
A.2.5.
</b>
</p>
</td>
<td align="left" valign="top">
<p>
Is there an advantage to using the
<code class="literal">
InnoDB
</code>
storage engine exclusively, as opposed to a combination of
<code class="literal">
InnoDB
</code>
and non-
<code class="literal">
InnoDB
</code>
storage engines?
</p>
</td>
</tr>
<tr class="answer">
<td align="left" valign="top">
</td>
<td align="left" valign="top">
<p>
Yes. Using
<code class="literal">
InnoDB
</code>
tables exclusively can
simplify backup and recovery operations. MySQL Enterprise Backup does a
<a class="link" href="glossary.html#glos_hot_backup" title="hot backup">
hot backup
</a>
of all tables
that use the
<code class="literal">
InnoDB
</code>
storage engine. For
tables using
<code class="literal">
MyISAM
</code>
or other
non-
<code class="literal">
InnoDB
</code>
storage engines, it does a
<span class="quote">
“
<span class="quote">
warm
</span>
”
</span>
backup, where the database continues to run,
but those tables cannot be modified while being backed up. See
<a class="xref" href="mysql-enterprise-backup.html" title="32.1 MySQL Enterprise Backup Overview">
Section 32.1, “MySQL Enterprise Backup Overview”
</a>
.
</p>
</td>
</tr>
<tr class="question">
<td align="left" valign="top">
<a name="faq-mysql-what-archive-engine">
</a>
<a name="idm46045056418032">
</a>
<p>
<b>
A.2.6.
</b>
</p>
</td>
<td align="left" valign="top">
<p>
What are the unique benefits of the
<code class="literal">
ARCHIVE
</code>
storage engine?
</p>
</td>
</tr>
<tr class="answer">
<td align="left" valign="top">
</td>
<td align="left" valign="top">
<p>
The
<code class="literal">
ARCHIVE
</code>
storage engine stores large
amounts of data without indexes; it has a small footprint, and
performs selects using table scans. See
<a class="xref" href="archive-storage-engine.html" title="18.5 The ARCHIVE Storage Engine">
Section 18.5, “The ARCHIVE Storage Engine”
</a>
, for details.
</p>
</td>
</tr>
</tbody>
</table>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/no-login-pluggable-authentication.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="no-login-pluggable-authentication">
</a>
8.4.1.9 No-Login Pluggable Authentication
</h4>
</div>
</div>
</div>
<a class="indexterm" name="idm46045244253744">
</a>
<a class="indexterm" name="idm46045244252656">
</a>
<p>
The
<code class="literal">
mysql_no_login
</code>
server-side authentication
plugin prevents all client connections to any account that uses
it. Use cases for this plugin include:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
Accounts that must be able to execute stored programs and
views with elevated privileges without exposing those
privileges to ordinary users.
</p>
</li>
<li class="listitem">
<p>
Proxied accounts that should never permit direct login but
are intended to be accessed only through proxy accounts.
</p>
</li>
</ul>
</div>
<p>
The following table shows the plugin and library file names. The
file name suffix might differ on your system. The file must be
located in the directory named by the
<a class="link" href="server-system-variables.html#sysvar_plugin_dir">
<code class="literal">
plugin_dir
</code>
</a>
system variable.
</p>
<div class="table">
<a name="idm46045244245760">
</a>
<p class="title">
<b>
Table 8.24 Plugin and Library Names for No-Login Authentication
</b>
</p>
<div class="table-contents">
<table summary="Names for the plugins and library file used for no-login password authentication.">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<thead>
<tr>
<th>
Plugin or File
</th>
<th>
Plugin or File Name
</th>
</tr>
</thead>
<tbody>
<tr>
<td>
Server-side plugin
</td>
<td>
<code class="literal">
mysql_no_login
</code>
</td>
</tr>
<tr>
<td>
Client-side plugin
</td>
<td>
None
</td>
</tr>
<tr>
<td>
Library file
</td>
<td>
<code class="filename">
mysql_no_login.so
</code>
</td>
</tr>
</tbody>
</table>
</div>
</div>
<br class="table-break"/>
<p>
The following sections provide installation and usage
information specific to no-login pluggable authentication:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<a class="xref" href="no-login-pluggable-authentication.html#no-login-pluggable-authentication-installation" title="Installing No-Login Pluggable Authentication">
Installing No-Login Pluggable Authentication
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="no-login-pluggable-authentication.html#no-login-pluggable-authentication-uninstallation" title="Uninstalling No-Login Pluggable Authentication">
Uninstalling No-Login Pluggable Authentication
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="no-login-pluggable-authentication.html#no-login-pluggable-authentication-usage" title="Using No-Login Pluggable Authentication">
Using No-Login Pluggable Authentication
</a>
</p>
</li>
</ul>
</div>
<p>
For general information about pluggable authentication in MySQL,
see
<a class="xref" href="pluggable-authentication.html" title="8.2.17 Pluggable Authentication">
Section 8.2.17, “Pluggable Authentication”
</a>
. For proxy user
information, see
<a class="xref" href="proxy-users.html" title="8.2.19 Proxy Users">
Section 8.2.19, “Proxy Users”
</a>
.
</p>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h5 class="title">
<a name="no-login-pluggable-authentication-installation">
</a>
Installing No-Login Pluggable Authentication
</h5>
</div>
</div>
</div>
<p>
This section describes how to install the no-login
authentication plugin. For general information about
installing plugins, see
<a class="xref" href="plugin-loading.html" title="7.6.1 Installing and Uninstalling Plugins">
Section 7.6.1, “Installing and Uninstalling Plugins”
</a>
.
</p>
<p>
To be usable by the server, the plugin library file must be
located in the MySQL plugin directory (the directory named by
the
<a class="link" href="server-system-variables.html#sysvar_plugin_dir">
<code class="literal">
plugin_dir
</code>
</a>
system
variable). If necessary, configure the plugin directory
location by setting the value of
<a class="link" href="server-system-variables.html#sysvar_plugin_dir">
<code class="literal">
plugin_dir
</code>
</a>
at server startup.
</p>
<p>
The plugin library file base name is
<code class="literal">
mysql_no_login
</code>
. The file name suffix
differs per platform (for example,
<code class="filename">
.so
</code>
for Unix and Unix-like systems,
<code class="filename">
.dll
</code>
for
Windows).
</p>
<p>
To load the plugin at server startup, use the
<a class="link" href="server-options.html#option_mysqld_plugin-load-add">
<code class="option">
--plugin-load-add
</code>
</a>
option to
name the library file that contains it. With this
plugin-loading method, the option must be given each time the
server starts. For example, put these lines in the server
<code class="filename">
my.cnf
</code>
file, adjusting the
<code class="filename">
.so
</code>
suffix for your platform as
necessary:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-ini"><div class="docs-select-all right" id="sa65575307"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-ini"><span class="token selector">[mysqld]</span>
<span class="token constant">plugin-load-add</span><span class="token attr-value"><span class="token punctuation">=</span>mysql_no_login.so</span></code></pre>
</div>
<p>
After modifying
<code class="filename">
my.cnf
</code>
, restart the
server to cause the new settings to take effect.
</p>
<p>
Alternatively, to load the plugin at runtime, use this
statement, adjusting the
<code class="filename">
.so
</code>
suffix for
your platform as necessary:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa39076875"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">INSTALL</span> <span class="token keyword">PLUGIN</span> mysql_no_login <span class="token keyword">SONAME</span> <span class="token string">'mysql_no_login.so'</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
<a class="link" href="install-plugin.html" title="15.7.4.4 INSTALL PLUGIN Statement">
<code class="literal">
INSTALL PLUGIN
</code>
</a>
loads the plugin
immediately, and also registers it in the
<code class="literal">
mysql.plugins
</code>
system table to cause the
server to load it for each subsequent normal startup without
the need for
<a class="link" href="server-options.html#option_mysqld_plugin-load-add">
<code class="option">
--plugin-load-add
</code>
</a>
.
</p>
<p>
To verify plugin installation, examine the Information Schema
<a class="link" href="information-schema-plugins-table.html" title="28.3.22 The INFORMATION_SCHEMA PLUGINS Table">
<code class="literal">
PLUGINS
</code>
</a>
table or use the
<a class="link" href="show-plugins.html" title="15.7.7.27 SHOW PLUGINS Statement">
<code class="literal">
SHOW PLUGINS
</code>
</a>
statement (see
<a class="xref" href="obtaining-plugin-information.html" title="7.6.2 Obtaining Server Plugin Information">
Section 7.6.2, “Obtaining Server Plugin Information”
</a>
). For example:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa8512579"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> PLUGIN_NAME<span class="token punctuation">,</span> PLUGIN_STATUS
<span class="token keyword">FROM</span> INFORMATION_SCHEMA<span class="token punctuation">.</span><span class="token keyword">PLUGINS</span>
<span class="token keyword">WHERE</span> PLUGIN_NAME <span class="token operator">LIKE</span> <span class="token string">'%login%'</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> PLUGIN_NAME <span class="token punctuation">|</span> PLUGIN_STATUS <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> mysql_no_login <span class="token punctuation">|</span> ACTIVE <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span></code></pre>
</div>
<p>
If the plugin fails to initialize, check the server error log
for diagnostic messages.
</p>
<p>
To associate MySQL accounts with the no-login plugin, see
<a class="xref" href="no-login-pluggable-authentication.html#no-login-pluggable-authentication-usage" title="Using No-Login Pluggable Authentication">
Using No-Login Pluggable Authentication
</a>
.
</p>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h5 class="title">
<a name="no-login-pluggable-authentication-uninstallation">
</a>
Uninstalling No-Login Pluggable Authentication
</h5>
</div>
</div>
</div>
<p>
The method used to uninstall the no-login authentication
plugin depends on how you installed it:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
If you installed the plugin at server startup using a
<a class="link" href="server-options.html#option_mysqld_plugin-load-add">
<code class="option">
--plugin-load-add
</code>
</a>
option,
restart the server without the option.
</p>
</li>
<li class="listitem">
<p>
If you installed the plugin at runtime using an
<a class="link" href="install-plugin.html" title="15.7.4.4 INSTALL PLUGIN Statement">
<code class="literal">
INSTALL PLUGIN
</code>
</a>
statement,
it remains installed across server restarts. To uninstall
it, use
<a class="link" href="uninstall-plugin.html" title="15.7.4.6 UNINSTALL PLUGIN Statement">
<code class="literal">
UNINSTALL PLUGIN
</code>
</a>
:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa55891216"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">UNINSTALL</span> <span class="token keyword">PLUGIN</span> mysql_no_login<span class="token punctuation">;</span></code></pre>
</div>
</li>
</ul>
</div>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h5 class="title">
<a name="no-login-pluggable-authentication-usage">
</a>
Using No-Login Pluggable Authentication
</h5>
</div>
</div>
</div>
<p>
This section describes how to use the no-login authentication
plugin to prevent accounts from being used for connecting from
MySQL client programs to the server. It is assumed that the
server is running with the no-login plugin enabled, as
described in
<a class="xref" href="no-login-pluggable-authentication.html#no-login-pluggable-authentication-installation" title="Installing No-Login Pluggable Authentication">
Installing No-Login Pluggable Authentication
</a>
.
</p>
<p>
To refer to the no-login authentication plugin in the
<code class="literal">
IDENTIFIED WITH
</code>
clause of a
<a class="link" href="create-user.html" title="15.7.1.3 CREATE USER Statement">
<code class="literal">
CREATE USER
</code>
</a>
statement, use the
name
<code class="literal">
mysql_no_login
</code>
.
</p>
<p>
An account that authenticates using
<code class="literal">
mysql_no_login
</code>
may be used as the
<code class="literal">
DEFINER
</code>
for stored program and view
objects. If such an object definition also includes
<code class="literal">
SQL SECURITY DEFINER
</code>
, it executes with that
account's privileges. DBAs can use this behavior to
provide access to confidential or sensitive data that is
exposed only through well-controlled interfaces.
</p>
<p>
The following example illustrates these principles. It defines
an account that does not permit client connections, and
associates with it a view that exposes only certain columns of
the
<code class="literal">
mysql.user
</code>
system table:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa30489229"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">DATABASE</span> nologindb<span class="token punctuation">;</span>
<span class="token keyword">CREATE</span> <span class="token keyword">USER</span> <span class="token string">'nologin'</span>@<span class="token string">'localhost'</span>
<span class="token keyword">IDENTIFIED</span> <span class="token keyword">WITH</span> mysql_no_login<span class="token punctuation">;</span>
<span class="token keyword">GRANT</span> <span class="token keyword">ALL</span> <span class="token keyword">ON</span> nologindb<span class="token punctuation">.</span><span class="token operator">*</span>
<span class="token keyword">TO</span> <span class="token string">'nologin'</span>@<span class="token string">'localhost'</span><span class="token punctuation">;</span>
<span class="token keyword">GRANT</span> <span class="token keyword">SELECT</span> <span class="token keyword">ON</span> mysql<span class="token punctuation">.</span><span class="token keyword">user</span>
<span class="token keyword">TO</span> <span class="token string">'nologin'</span>@<span class="token string">'localhost'</span><span class="token punctuation">;</span>
<span class="token keyword">CREATE</span> <span class="token keyword">DEFINER</span> <span class="token operator">=</span> <span class="token string">'nologin'</span>@<span class="token string">'localhost'</span>
<span class="token keyword">SQL</span> <span class="token keyword">SECURITY</span> <span class="token keyword">DEFINER</span>
<span class="token keyword">VIEW</span> nologindb<span class="token punctuation">.</span>myview
<span class="token keyword">AS</span> <span class="token keyword">SELECT</span> <span class="token keyword">User</span><span class="token punctuation">,</span> <span class="token keyword">Host</span> <span class="token keyword">FROM</span> mysql<span class="token punctuation">.</span><span class="token keyword">user</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
To provide protected access to the view to an ordinary user,
do this:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa74076063"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">GRANT</span> <span class="token keyword">SELECT</span> <span class="token keyword">ON</span> nologindb<span class="token punctuation">.</span>myview
<span class="token keyword">TO</span> <span class="token string">'ordinaryuser'</span>@<span class="token string">'localhost'</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
Now the ordinary user can use the view to access the limited
information it presents:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa16613530"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> nologindb<span class="token punctuation">.</span>myview<span class="token punctuation">;</span></code></pre>
</div>
<p>
Attempts by the user to access columns other than those
exposed by the view result in an error, as do attempts to
select from the view by users not granted access to it.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
Because the
<code class="literal">
nologin
</code>
account cannot be
used directly, the operations required to set up objects
that it uses must be performed by
<code class="literal">
root
</code>
or
similar account that has the privileges required to create
the objects and set
<code class="literal">
DEFINER
</code>
values.
</p>
</div>
<p>
The
<code class="literal">
mysql_no_login
</code>
plugin is also useful in
proxying scenarios. (For a discussion of concepts involved in
proxying, see
<a class="xref" href="proxy-users.html" title="8.2.19 Proxy Users">
Section 8.2.19, “Proxy Users”
</a>
.) An account that
authenticates using
<code class="literal">
mysql_no_login
</code>
may be
used as a proxied user for proxy accounts:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa49768817"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token comment" spellcheck="true">-- create proxied account</span>
<span class="token keyword">CREATE</span> <span class="token keyword">USER</span> <span class="token string">'proxied_user'</span>@<span class="token string">'localhost'</span>
<span class="token keyword">IDENTIFIED</span> <span class="token keyword">WITH</span> mysql_no_login<span class="token punctuation">;</span>
<span class="token comment" spellcheck="true">-- grant privileges to proxied account</span>
<span class="token keyword">GRANT</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token keyword">ON</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token keyword">TO</span> <span class="token string">'proxied_user'</span>@<span class="token string">'localhost'</span><span class="token punctuation">;</span>
<span class="token comment" spellcheck="true">-- permit proxy_user to be a proxy account for proxied account</span>
<span class="token keyword">GRANT</span> <span class="token keyword">PROXY</span>
<span class="token keyword">ON</span> <span class="token string">'proxied_user'</span>@<span class="token string">'localhost'</span>
<span class="token keyword">TO</span> <span class="token string">'proxy_user'</span>@<span class="token string">'localhost'</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
This enables clients to access MySQL through the proxy account
(
<code class="literal">
proxy_user
</code>
) but not to bypass the proxy
mechanism by connecting directly as the proxied user
(
<code class="literal">
proxied_user
</code>
). A client who connects using
the
<code class="literal">
proxy_user
</code>
account has the privileges
of the
<code class="literal">
proxied_user
</code>
account, but
<code class="literal">
proxied_user
</code>
itself cannot be used to
connect.
</p>
<p>
For alternative methods of protecting proxied accounts against
direct use, see
<a class="xref" href="proxy-users.html#preventing-proxied-account-direct-login" title="Preventing Direct Login to Proxied Accounts">
Preventing Direct Login to Proxied Accounts
</a>
.
</p>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/replication-features-repair-table.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="replication-features-repair-table">
</a>
19.5.1.25 Replication and REPAIR TABLE
</h4>
</div>
</div>
</div>
<a class="indexterm" name="idm46045135244352">
</a>
<a class="indexterm" name="idm46045135242848">
</a>
<p>
When used on a corrupted or otherwise damaged table, it is
possible for the
<a class="link" href="repair-table.html" title="15.7.3.5 REPAIR TABLE Statement">
<code class="literal">
REPAIR TABLE
</code>
</a>
statement to delete rows that cannot be recovered. However, any
such modifications of table data performed by this statement are
not replicated, which can cause source and replica to lose
synchronization. For this reason, in the event that a table on
the source becomes damaged and you use
<a class="link" href="repair-table.html" title="15.7.3.5 REPAIR TABLE Statement">
<code class="literal">
REPAIR TABLE
</code>
</a>
to repair it, you
should first stop replication (if it is still running) before
using
<a class="link" href="repair-table.html" title="15.7.3.5 REPAIR TABLE Statement">
<code class="literal">
REPAIR TABLE
</code>
</a>
, then
afterward compare the source's and replica's copies of
the table and be prepared to correct any discrepancies manually,
before restarting replication.
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/innodb-disk-io.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="innodb-disk-io">
</a>
17.11.1 InnoDB Disk I/O
</h3>
</div>
</div>
</div>
<a class="indexterm" name="idm46045160724544">
</a>
<p>
<code class="literal">
InnoDB
</code>
uses asynchronous disk I/O where
possible, by creating a number of threads to handle I/O
operations, while permitting other database operations to proceed
while the I/O is still in progress. On Linux and Windows
platforms,
<code class="literal">
InnoDB
</code>
uses the available OS and
library functions to perform
<span class="quote">
“
<span class="quote">
native
</span>
”
</span>
asynchronous
I/O. On other platforms,
<code class="literal">
InnoDB
</code>
still uses I/O
threads, but the threads may actually wait for I/O requests to
complete; this technique is known as
<span class="quote">
“
<span class="quote">
simulated
</span>
”
</span>
asynchronous I/O.
</p>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h4 class="title">
<a name="innodb-disk-io-read-ahead">
</a>
Read-Ahead
</h4>
</div>
</div>
</div>
<p>
If
<code class="literal">
InnoDB
</code>
can determine there is a high
probability that data might be needed soon, it performs
read-ahead operations to bring that data into the buffer pool so
that it is available in memory. Making a few large read requests
for contiguous data can be more efficient than making several
small, spread-out requests. There are two read-ahead heuristics
in
<code class="literal">
InnoDB
</code>
:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
In sequential read-ahead, if
<code class="literal">
InnoDB
</code>
notices that the access pattern to a segment in the
tablespace is sequential, it posts in advance a batch of
reads of database pages to the I/O system.
</p>
</li>
<li class="listitem">
<p>
In random read-ahead, if
<code class="literal">
InnoDB
</code>
notices
that some area in a tablespace seems to be in the process of
being fully read into the buffer pool, it posts the
remaining reads to the I/O system.
</p>
</li>
</ul>
</div>
<p>
For information about configuring read-ahead heuristics, see
<a class="xref" href="innodb-performance-read_ahead.html" title="17.8.3.4 Configuring InnoDB Buffer Pool Prefetching (Read-Ahead)">
Section 17.8.3.4, “Configuring InnoDB Buffer Pool Prefetching (Read-Ahead)”
</a>
.
</p>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h4 class="title">
<a name="innodb-disk-io-doublewrite">
</a>
Doublewrite Buffer
</h4>
</div>
</div>
</div>
<a class="indexterm" name="idm46045160709360">
</a>
<a class="indexterm" name="idm46045160708288">
</a>
<p>
<code class="literal">
InnoDB
</code>
uses a novel file flush technique
involving a structure called the
<a class="link" href="glossary.html#glos_doublewrite_buffer" title="doublewrite buffer">
doublewrite
buffer
</a>
, which is enabled by default in most cases
(
<a class="link" href="innodb-parameters.html#sysvar_innodb_doublewrite">
<code class="literal">
innodb_doublewrite=ON
</code>
</a>
). It
adds safety to recovery following an unexpected exit or power
outage, and improves performance on most varieties of Unix by
reducing the need for
<code class="literal">
fsync()
</code>
operations.
</p>
<p>
Before writing pages to a data file,
<code class="literal">
InnoDB
</code>
first writes them to a storage area called the doublewrite
buffer. Only after the write and the flush to the doublewrite
buffer has completed does
<code class="literal">
InnoDB
</code>
write the
pages to their proper positions in the data file. If there is an
operating system, storage subsystem, or unexpected
<a class="link" href="mysqld.html" title="6.3.1 mysqld — The MySQL Server">
<span class="command">
<strong>
mysqld
</strong>
</span>
</a>
process exit in the middle of a page
write (causing a
<a class="link" href="glossary.html#glos_torn_page" title="torn page">
torn page
</a>
condition),
<code class="literal">
InnoDB
</code>
can later find a good copy
of the page from the doublewrite buffer during recovery.
</p>
<p>
For more information about the doublewrite buffer, see
<a class="xref" href="innodb-doublewrite-buffer.html" title="17.6.4 Doublewrite Buffer">
Section 17.6.4, “Doublewrite Buffer”
</a>
.
</p>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/fulltext-natural-language.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="fulltext-natural-language">
</a>
14.9.1 Natural Language Full-Text Searches
</h3>
</div>
</div>
</div>
<p>
By default or with the
<code class="literal">
IN NATURAL LANGUAGE
MODE
</code>
modifier, the
<a class="link" href="fulltext-search.html#function_match">
<code class="literal">
MATCH()
</code>
</a>
function performs a
natural language search for a string against a
<span class="firstterm">
text collection
</span>
. A
collection is a set of one or more columns included in a
<code class="literal">
FULLTEXT
</code>
index. The search string is given as
the argument to
<code class="literal">
AGAINST()
</code>
. For each row in
the table,
<a class="link" href="fulltext-search.html#function_match">
<code class="literal">
MATCH()
</code>
</a>
returns a
relevance value; that is, a similarity measure between the
search string and the text in that row in the columns named in
the
<a class="link" href="fulltext-search.html#function_match">
<code class="literal">
MATCH()
</code>
</a>
list.
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa83443748"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> articles <span class="token punctuation">(</span>
<span class="token prompt"> -></span> id <span class="token datatype">INT</span> <span class="token keyword">UNSIGNED</span> <span class="token keyword">AUTO_INCREMENT</span> <span class="token operator">NOT</span> <span class="token boolean">NULL</span> <span class="token keyword">PRIMARY</span> <span class="token keyword">KEY</span><span class="token punctuation">,</span>
<span class="token prompt"> -></span> title <span class="token datatype">VARCHAR</span><span class="token punctuation">(</span><span class="token number">200</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
<span class="token prompt"> -></span> body <span class="token datatype">TEXT</span><span class="token punctuation">,</span>
<span class="token prompt"> -></span> <span class="token keyword">FULLTEXT</span> <span class="token punctuation">(</span>title<span class="token punctuation">,</span>body<span class="token punctuation">)</span>
<span class="token prompt"> -></span> <span class="token punctuation">)</span> <span class="token keyword">ENGINE</span><span class="token operator">=</span>InnoDB<span class="token punctuation">;</span>
<span class="token output">Query OK, 0 rows affected (0.08 sec)</span>
<span class="token prompt">mysql></span> <span class="token keyword">INSERT</span> <span class="token keyword">INTO</span> articles <span class="token punctuation">(</span>title<span class="token punctuation">,</span>body<span class="token punctuation">)</span> <span class="token keyword">VALUES</span>
<span class="token prompt"> -></span> <span class="token punctuation">(</span><span class="token string">'MySQL Tutorial'</span><span class="token punctuation">,</span><span class="token string">'DBMS stands for DataBase ...'</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
<span class="token prompt"> -></span> <span class="token punctuation">(</span><span class="token string">'How To Use MySQL Well'</span><span class="token punctuation">,</span><span class="token string">'After you went through a ...'</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
<span class="token prompt"> -></span> <span class="token punctuation">(</span><span class="token string">'Optimizing MySQL'</span><span class="token punctuation">,</span><span class="token string">'In this tutorial, we show ...'</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
<span class="token prompt"> -></span> <span class="token punctuation">(</span><span class="token string">'1001 MySQL Tricks'</span><span class="token punctuation">,</span><span class="token string">'1. Never run mysqld as root. 2. ...'</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
<span class="token prompt"> -></span> <span class="token punctuation">(</span><span class="token string">'MySQL vs. YourSQL'</span><span class="token punctuation">,</span><span class="token string">'In the following database comparison ...'</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
<span class="token prompt"> -></span> <span class="token punctuation">(</span><span class="token string">'MySQL Security'</span><span class="token punctuation">,</span><span class="token string">'When configured properly, MySQL ...'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token output">Query OK, 6 rows affected (0.01 sec)</span>
<span class="token output">Records: 6 Duplicates: 0 Warnings: 0</span>
<span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> articles
<span class="token prompt"> -></span> <span class="token keyword">WHERE</span> <span class="token operator">MATCH</span> <span class="token punctuation">(</span>title<span class="token punctuation">,</span>body<span class="token punctuation">)</span>
<span class="token prompt"> -></span> <span class="token keyword">AGAINST</span> <span class="token punctuation">(</span><span class="token string">'database'</span> <span class="token keyword">IN</span> <span class="token keyword">NATURAL</span> <span class="token keyword">LANGUAGE</span> <span class="token keyword">MODE</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> id <span class="token punctuation">|</span> title <span class="token punctuation">|</span> body <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> 1 <span class="token punctuation">|</span> MySQL Tutorial <span class="token punctuation">|</span> DBMS stands for DataBase ... <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> 5 <span class="token punctuation">|</span> MySQL vs. YourSQL <span class="token punctuation">|</span> In the following database comparison ... <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output">2 rows in set (0.00 sec)</span></code></pre>
</div>
<p>
By default, the search is performed in case-insensitive fashion.
To perform a case-sensitive full-text search, use a
case-sensitive or binary collation for the indexed columns. For
example, a column that uses the
<code class="literal">
utf8mb4
</code>
character set of can be assigned a collation of
<code class="literal">
utf8mb4_0900_as_cs
</code>
or
<code class="literal">
utf8mb4_bin
</code>
to make it case-sensitive for
full-text searches.
</p>
<p>
When
<a class="link" href="fulltext-search.html#function_match">
<code class="literal">
MATCH()
</code>
</a>
is used in a
<code class="literal">
WHERE
</code>
clause, as in the example shown
earlier, the rows returned are automatically sorted with the
highest relevance first as long as the following conditions are
met:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
There must be no explicit
<code class="literal">
ORDER BY
</code>
clause.
</p>
</li>
<li class="listitem">
<p>
The search must be performed using a full-text index scan
rather than a table scan.
</p>
</li>
<li class="listitem">
<p>
If the query joins tables, the full-text index scan must be
the leftmost non-constant table in the join.
</p>
</li>
</ul>
</div>
<p>
Given the conditions just listed, it is usually less effort to
specify using
<code class="literal">
ORDER BY
</code>
an explicit sort order
when one is necessary or desired.
</p>
<p>
Relevance values are nonnegative floating-point numbers. Zero
relevance means no similarity. Relevance is computed based on
the number of words in the row (document), the number of unique
words in the row, the total number of words in the collection,
and the number of rows that contain a particular word.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
The term
<span class="quote">
“
<span class="quote">
document
</span>
”
</span>
may be used interchangeably
with the term
<span class="quote">
“
<span class="quote">
row
</span>
”
</span>
, and both terms refer to the
indexed part of the row. The term
<span class="quote">
“
<span class="quote">
collection
</span>
”
</span>
refers to the indexed columns and encompasses all rows.
</p>
</div>
<p>
To simply count matches, you could use a query like this:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa62668929"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token function">COUNT</span><span class="token punctuation">(</span><span class="token operator">*</span><span class="token punctuation">)</span> <span class="token keyword">FROM</span> articles
<span class="token prompt"> -></span> <span class="token keyword">WHERE</span> <span class="token operator">MATCH</span> <span class="token punctuation">(</span>title<span class="token punctuation">,</span>body<span class="token punctuation">)</span>
<span class="token prompt"> -></span> <span class="token keyword">AGAINST</span> <span class="token punctuation">(</span><span class="token string">'database'</span> <span class="token keyword">IN</span> <span class="token keyword">NATURAL</span> <span class="token keyword">LANGUAGE</span> <span class="token keyword">MODE</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> COUNT(*) <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> 2 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output">1 row in set (0.00 sec)</span></code></pre>
</div>
<p>
You might find it quicker to rewrite the query as follows:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa75241634"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SELECT</span>
<span class="token prompt"> -></span> <span class="token function">COUNT</span><span class="token punctuation">(</span><span class="token function">IF</span><span class="token punctuation">(</span><span class="token operator">MATCH</span> <span class="token punctuation">(</span>title<span class="token punctuation">,</span>body<span class="token punctuation">)</span> <span class="token keyword">AGAINST</span> <span class="token punctuation">(</span><span class="token string">'database'</span> <span class="token keyword">IN</span> <span class="token keyword">NATURAL</span> <span class="token keyword">LANGUAGE</span> <span class="token keyword">MODE</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token number">1</span><span class="token punctuation">,</span> <span class="token boolean">NULL</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
<span class="token prompt"> -></span> <span class="token keyword">AS</span> count
<span class="token prompt"> -></span> <span class="token keyword">FROM</span> articles<span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> count <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> 2 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output">1 row in set (0.03 sec)</span></code></pre>
</div>
<p>
The first query does some extra work (sorting the results by
relevance) but also can use an index lookup based on the
<code class="literal">
WHERE
</code>
clause. The index lookup might make the
first query faster if the search matches few rows. The second
query performs a full table scan, which might be faster than the
index lookup if the search term was present in most rows.
</p>
<p>
For natural-language full-text searches, the columns named in
the
<a class="link" href="fulltext-search.html#function_match">
<code class="literal">
MATCH()
</code>
</a>
function must be the
same columns included in some
<code class="literal">
FULLTEXT
</code>
index
in your table. For the preceding query, note that the columns
named in the
<a class="link" href="fulltext-search.html#function_match">
<code class="literal">
MATCH()
</code>
</a>
function
(
<code class="literal">
title
</code>
and
<code class="literal">
body
</code>
) are the
same as those named in the definition of the
<code class="literal">
article
</code>
table's
<code class="literal">
FULLTEXT
</code>
index. To search the
<code class="literal">
title
</code>
or
<code class="literal">
body
</code>
separately, you would create separate
<code class="literal">
FULLTEXT
</code>
indexes for each column.
</p>
<p>
You can also perform a boolean search or a search with query
expansion. These search types are described in
<a class="xref" href="fulltext-boolean.html" title="14.9.2 Boolean Full-Text Searches">
Section 14.9.2, “Boolean Full-Text Searches”
</a>
, and
<a class="xref" href="fulltext-query-expansion.html" title="14.9.3 Full-Text Searches with Query Expansion">
Section 14.9.3, “Full-Text Searches with Query Expansion”
</a>
.
</p>
<p>
A full-text search that uses an index can name columns only from
a single table in the
<a class="link" href="fulltext-search.html#function_match">
<code class="literal">
MATCH()
</code>
</a>
clause because an index cannot span multiple tables. For
<code class="literal">
MyISAM
</code>
tables, a boolean search can be done
in the absence of an index (albeit more slowly), in which case
it is possible to name columns from multiple tables.
</p>
<p>
The preceding example is a basic illustration that shows how to
use the
<a class="link" href="fulltext-search.html#function_match">
<code class="literal">
MATCH()
</code>
</a>
function where
rows are returned in order of decreasing relevance. The next
example shows how to retrieve the relevance values explicitly.
Returned rows are not ordered because the
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT
</code>
</a>
statement includes neither
<code class="literal">
WHERE
</code>
nor
<code class="literal">
ORDER BY
</code>
clauses:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa43793286"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> id<span class="token punctuation">,</span> <span class="token operator">MATCH</span> <span class="token punctuation">(</span>title<span class="token punctuation">,</span>body<span class="token punctuation">)</span>
<span class="token prompt"> -></span> <span class="token keyword">AGAINST</span> <span class="token punctuation">(</span><span class="token string">'Tutorial'</span> <span class="token keyword">IN</span> <span class="token keyword">NATURAL</span> <span class="token keyword">LANGUAGE</span> <span class="token keyword">MODE</span><span class="token punctuation">)</span> <span class="token keyword">AS</span> score
<span class="token prompt"> -></span> <span class="token keyword">FROM</span> articles<span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> id <span class="token punctuation">|</span> score <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> 1 <span class="token punctuation">|</span> 0.22764469683170319 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> 2 <span class="token punctuation">|</span> 0 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> 3 <span class="token punctuation">|</span> 0.22764469683170319 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> 4 <span class="token punctuation">|</span> 0 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> 5 <span class="token punctuation">|</span> 0 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> 6 <span class="token punctuation">|</span> 0 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output">6 rows in set (0.00 sec)</span></code></pre>
</div>
<p>
The following example is more complex. The query returns the
relevance values and it also sorts the rows in order of
decreasing relevance. To achieve this result, specify
<a class="link" href="fulltext-search.html#function_match">
<code class="literal">
MATCH()
</code>
</a>
twice: once in the
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT
</code>
</a>
list and once in the
<code class="literal">
WHERE
</code>
clause. This causes no additional
overhead, because the MySQL optimizer notices that the two
<a class="link" href="fulltext-search.html#function_match">
<code class="literal">
MATCH()
</code>
</a>
calls are identical and
invokes the full-text search code only once.
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa58882847"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> id<span class="token punctuation">,</span> body<span class="token punctuation">,</span> <span class="token operator">MATCH</span> <span class="token punctuation">(</span>title<span class="token punctuation">,</span>body<span class="token punctuation">)</span>
<span class="token prompt"> -></span> <span class="token keyword">AGAINST</span> <span class="token punctuation">(</span><span class="token string">'Security implications of running MySQL as root'</span>
<span class="token prompt"> -></span> <span class="token keyword">IN</span> <span class="token keyword">NATURAL</span> <span class="token keyword">LANGUAGE</span> <span class="token keyword">MODE</span><span class="token punctuation">)</span> <span class="token keyword">AS</span> score
<span class="token prompt"> -></span> <span class="token keyword">FROM</span> articles
<span class="token prompt"> -></span> <span class="token keyword">WHERE</span> <span class="token operator">MATCH</span> <span class="token punctuation">(</span>title<span class="token punctuation">,</span>body<span class="token punctuation">)</span>
<span class="token prompt"> -></span> <span class="token keyword">AGAINST</span><span class="token punctuation">(</span><span class="token string">'Security implications of running MySQL as root'</span>
<span class="token prompt"> -></span> <span class="token keyword">IN</span> <span class="token keyword">NATURAL</span> <span class="token keyword">LANGUAGE</span> <span class="token keyword">MODE</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> id <span class="token punctuation">|</span> body <span class="token punctuation">|</span> score <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> 4 <span class="token punctuation">|</span> 1. Never run mysqld as root. 2. ... <span class="token punctuation">|</span> 1.5219271183014 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> 6 <span class="token punctuation">|</span> When configured properly, MySQL ... <span class="token punctuation">|</span> 1.3114095926285 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output">2 rows in set (0.00 sec)</span></code></pre>
</div>
<p>
A phrase that is enclosed within double quote
(
<code class="literal">
"
</code>
) characters matches only rows that contain
the phrase
<span class="emphasis">
<em>
literally, as it was typed
</em>
</span>
. The
full-text engine splits the phrase into words and performs a
search in the
<code class="literal">
FULLTEXT
</code>
index for the words.
Nonword characters need not be matched exactly: Phrase searching
requires only that matches contain exactly the same words as the
phrase and in the same order. For example,
<code class="literal">
"test
phrase"
</code>
matches
<code class="literal">
"test, phrase"
</code>
. If
the phrase contains no words that are in the index, the result
is empty. For example, if all words are either stopwords or
shorter than the minimum length of indexed words, the result is
empty.
</p>
<p>
The MySQL
<code class="literal">
FULLTEXT
</code>
implementation regards any
sequence of true word characters (letters, digits, and
underscores) as a word. That sequence may also contain
apostrophes (
<code class="literal">
'
</code>
), but not more than one in a
row. This means that
<code class="literal">
aaa'bbb
</code>
is regarded as
one word, but
<code class="literal">
aaa''bbb
</code>
is regarded as two
words. Apostrophes at the beginning or the end of a word are
stripped by the
<code class="literal">
FULLTEXT
</code>
parser;
<code class="literal">
'aaa'bbb'
</code>
would be parsed as
<code class="literal">
aaa'bbb
</code>
.
</p>
<p>
The built-in
<code class="literal">
FULLTEXT
</code>
parser determines where
words start and end by looking for certain delimiter characters;
for example,
<code class="literal">
</code>
(space),
<code class="literal">
,
</code>
(comma), and
<code class="literal">
.
</code>
(period).
If words are not separated by delimiters (as in, for example,
Chinese), the built-in
<code class="literal">
FULLTEXT
</code>
parser cannot
determine where a word begins or ends. To be able to add words
or other indexed terms in such languages to a
<code class="literal">
FULLTEXT
</code>
index that uses the built-in
<code class="literal">
FULLTEXT
</code>
parser, you must preprocess them so
that they are separated by some arbitrary delimiter.
Alternatively, you can create
<code class="literal">
FULLTEXT
</code>
indexes using the ngram parser plugin (for Chinese, Japanese, or
Korean) or the MeCab parser plugin (for Japanese).
</p>
<p>
It is possible to write a plugin that replaces the built-in
full-text parser. For details, see
<a class="ulink" href="/doc/extending-mysql/8.4/en/plugin-api.html" target="_top">
The MySQL Plugin API
</a>
.
For example parser plugin source code, see the
<code class="filename">
plugin/fulltext
</code>
directory of a MySQL source
distribution.
</p>
<p>
Some words are ignored in full-text searches:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
Any word that is too short is ignored. The default minimum
length of words that are found by full-text searches is
three characters for
<code class="literal">
InnoDB
</code>
search
indexes, or four characters for
<code class="literal">
MyISAM
</code>
.
You can control the cutoff by setting a configuration option
before creating the index:
<a class="link" href="innodb-parameters.html#sysvar_innodb_ft_min_token_size">
<code class="literal">
innodb_ft_min_token_size
</code>
</a>
configuration option for
<code class="literal">
InnoDB
</code>
search
indexes, or
<a class="link" href="server-system-variables.html#sysvar_ft_min_word_len">
<code class="literal">
ft_min_word_len
</code>
</a>
for
<code class="literal">
MyISAM
</code>
.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
This behavior does not apply to
<code class="literal">
FULLTEXT
</code>
indexes that use the ngram
parser. For the ngram parser, token length is defined by
the
<a class="link" href="server-system-variables.html#sysvar_ngram_token_size">
<code class="literal">
ngram_token_size
</code>
</a>
option.
</p>
</div>
</li>
<li class="listitem">
<p>
Words in the stopword list are ignored. A stopword is a word
such as
<span class="quote">
“
<span class="quote">
the
</span>
”
</span>
or
<span class="quote">
“
<span class="quote">
some
</span>
”
</span>
that is so
common that it is considered to have zero semantic value.
There is a built-in stopword list, but it can be overridden
by a user-defined list. The stopword lists and related
configuration options are different for
<code class="literal">
InnoDB
</code>
search indexes and
<code class="literal">
MyISAM
</code>
ones. Stopword processing is
controlled by the configuration options
<a class="link" href="innodb-parameters.html#sysvar_innodb_ft_enable_stopword">
<code class="literal">
innodb_ft_enable_stopword
</code>
</a>
,
<a class="link" href="innodb-parameters.html#sysvar_innodb_ft_server_stopword_table">
<code class="literal">
innodb_ft_server_stopword_table
</code>
</a>
,
and
<a class="link" href="innodb-parameters.html#sysvar_innodb_ft_user_stopword_table">
<code class="literal">
innodb_ft_user_stopword_table
</code>
</a>
for
<code class="literal">
InnoDB
</code>
search indexes, and
<a class="link" href="server-system-variables.html#sysvar_ft_stopword_file">
<code class="literal">
ft_stopword_file
</code>
</a>
for
<code class="literal">
MyISAM
</code>
ones.
</p>
</li>
</ul>
</div>
<p>
See
<a class="xref" href="fulltext-stopwords.html" title="14.9.4 Full-Text Stopwords">
Section 14.9.4, “Full-Text Stopwords”
</a>
to view default
stopword lists and how to change them. The default minimum word
length can be changed as described in
<a class="xref" href="fulltext-fine-tuning.html" title="14.9.6 Fine-Tuning MySQL Full-Text Search">
Section 14.9.6, “Fine-Tuning MySQL Full-Text Search”
</a>
.
</p>
<p>
Every correct word in the collection and in the query is
weighted according to its significance in the collection or
query. Thus, a word that is present in many documents has a
lower weight, because it has lower semantic value in this
particular collection. Conversely, if the word is rare, it
receives a higher weight. The weights of the words are combined
to compute the relevance of the row. This technique works best
with large collections.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
MyISAM Limitation
</div>
<p>
For very small tables, word distribution does not adequately
reflect their semantic value, and this model may sometimes
produce bizarre results for search indexes on
<code class="literal">
MyISAM
</code>
tables. For example, although the
word
<span class="quote">
“
<span class="quote">
MySQL
</span>
”
</span>
is present in every row of the
<code class="literal">
articles
</code>
table shown earlier, a search for
the word in a
<code class="literal">
MyISAM
</code>
search index produces
no results:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa94773246"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> articles
<span class="token prompt"> -></span> <span class="token keyword">WHERE</span> <span class="token operator">MATCH</span> <span class="token punctuation">(</span>title<span class="token punctuation">,</span>body<span class="token punctuation">)</span>
<span class="token prompt"> -></span> <span class="token keyword">AGAINST</span> <span class="token punctuation">(</span><span class="token string">'MySQL'</span> <span class="token keyword">IN</span> <span class="token keyword">NATURAL</span> <span class="token keyword">LANGUAGE</span> <span class="token keyword">MODE</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token output">Empty set (0.00 sec)</span></code></pre>
</div>
<p>
The search result is empty because the word
<span class="quote">
“
<span class="quote">
MySQL
</span>
”
</span>
is present in at least 50% of the rows,
and so is effectively treated as a stopword. This filtering
technique is more suitable for large data sets, where you
might not want the result set to return every second row from
a 1GB table, than for small data sets where it might cause
poor results for popular terms.
</p>
<p>
The 50% threshold can surprise you when you first try
full-text searching to see how it works, and makes
<code class="literal">
InnoDB
</code>
tables more suited to
experimentation with full-text searches. If you create a
<code class="literal">
MyISAM
</code>
table and insert only one or two
rows of text into it, every word in the text occurs in at
least 50% of the rows. As a result, no search returns any
results until the table contains more rows. Users who need to
bypass the 50% limitation can build search indexes on
<code class="literal">
InnoDB
</code>
tables, or use the boolean search
mode explained in
<a class="xref" href="fulltext-boolean.html" title="14.9.2 Boolean Full-Text Searches">
Section 14.9.2, “Boolean Full-Text Searches”
</a>
.
</p>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/mysql-cluster-programs-ndbmtd.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="mysql-cluster-programs-ndbmtd">
</a>
25.5.3 ndbmtd — The NDB Cluster Data Node Daemon (Multi-Threaded)
</h3>
</div>
</div>
</div>
<a class="indexterm" name="idm46045107293824">
</a>
<a class="indexterm" name="idm46045107292880">
</a>
<a class="indexterm" name="idm46045107291520">
</a>
<a class="indexterm" name="idm46045107290160">
</a>
<a class="indexterm" name="idm46045107289248">
</a>
<p>
<a class="link" href="mysql-cluster-programs-ndbmtd.html" title="25.5.3 ndbmtd — The NDB Cluster Data Node Daemon (Multi-Threaded)">
<span class="command">
<strong>
ndbmtd
</strong>
</span>
</a>
is a multithreaded version of
<a class="link" href="mysql-cluster-programs-ndbd.html" title="25.5.1 ndbd — The NDB Cluster Data Node Daemon">
<span class="command">
<strong>
ndbd
</strong>
</span>
</a>
, the process that is used to handle all
the data in tables using the
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDBCLUSTER
</code>
</a>
storage engine.
<a class="link" href="mysql-cluster-programs-ndbmtd.html" title="25.5.3 ndbmtd — The NDB Cluster Data Node Daemon (Multi-Threaded)">
<span class="command">
<strong>
ndbmtd
</strong>
</span>
</a>
is intended for use on host computers
having multiple CPU cores. Except where otherwise noted,
<a class="link" href="mysql-cluster-programs-ndbmtd.html" title="25.5.3 ndbmtd — The NDB Cluster Data Node Daemon (Multi-Threaded)">
<span class="command">
<strong>
ndbmtd
</strong>
</span>
</a>
functions in the same way as
<a class="link" href="mysql-cluster-programs-ndbd.html" title="25.5.1 ndbd — The NDB Cluster Data Node Daemon">
<span class="command">
<strong>
ndbd
</strong>
</span>
</a>
; therefore, in this section, we
concentrate on the ways in which
<a class="link" href="mysql-cluster-programs-ndbmtd.html" title="25.5.3 ndbmtd — The NDB Cluster Data Node Daemon (Multi-Threaded)">
<span class="command">
<strong>
ndbmtd
</strong>
</span>
</a>
differs from
<a class="link" href="mysql-cluster-programs-ndbd.html" title="25.5.1 ndbd — The NDB Cluster Data Node Daemon">
<span class="command">
<strong>
ndbd
</strong>
</span>
</a>
, and you should consult
<a class="xref" href="mysql-cluster-programs-ndbd.html" title="25.5.1 ndbd — The NDB Cluster Data Node Daemon">
Section 25.5.1, “ndbd — The NDB Cluster Data Node Daemon”
</a>
, for additional
information about running NDB Cluster data nodes that apply to
both the single-threaded and multithreaded versions of the data
node process.
</p>
<p>
Command-line options and configuration parameters used with
<a class="link" href="mysql-cluster-programs-ndbd.html" title="25.5.1 ndbd — The NDB Cluster Data Node Daemon">
<span class="command">
<strong>
ndbd
</strong>
</span>
</a>
also apply to
<a class="link" href="mysql-cluster-programs-ndbmtd.html" title="25.5.3 ndbmtd — The NDB Cluster Data Node Daemon (Multi-Threaded)">
<span class="command">
<strong>
ndbmtd
</strong>
</span>
</a>
.
For more information about these options and parameters, see
<a class="xref" href="mysql-cluster-programs-ndbd.html" title="25.5.1 ndbd — The NDB Cluster Data Node Daemon">
Section 25.5.1, “ndbd — The NDB Cluster Data Node Daemon”
</a>
, and
<a class="xref" href="mysql-cluster-ndbd-definition.html" title="25.4.3.6 Defining NDB Cluster Data Nodes">
Section 25.4.3.6, “Defining NDB Cluster Data Nodes”
</a>
, respectively.
</p>
<p>
<a class="link" href="mysql-cluster-programs-ndbmtd.html" title="25.5.3 ndbmtd — The NDB Cluster Data Node Daemon (Multi-Threaded)">
<span class="command">
<strong>
ndbmtd
</strong>
</span>
</a>
is also file system-compatible with
<a class="link" href="mysql-cluster-programs-ndbd.html" title="25.5.1 ndbd — The NDB Cluster Data Node Daemon">
<span class="command">
<strong>
ndbd
</strong>
</span>
</a>
. In other words, a data node running
<a class="link" href="mysql-cluster-programs-ndbd.html" title="25.5.1 ndbd — The NDB Cluster Data Node Daemon">
<span class="command">
<strong>
ndbd
</strong>
</span>
</a>
can be stopped, the binary replaced with
<a class="link" href="mysql-cluster-programs-ndbmtd.html" title="25.5.3 ndbmtd — The NDB Cluster Data Node Daemon (Multi-Threaded)">
<span class="command">
<strong>
ndbmtd
</strong>
</span>
</a>
, and then restarted without any loss
of data. (However, when doing this, you must make sure that
<a class="link" href="mysql-cluster-ndbd-definition.html#ndbparam-ndbmtd-maxnoofexecutionthreads">
<code class="literal">
MaxNoOfExecutionThreads
</code>
</a>
is set to an appropriate value before restarting the node if you
wish for
<a class="link" href="mysql-cluster-programs-ndbmtd.html" title="25.5.3 ndbmtd — The NDB Cluster Data Node Daemon (Multi-Threaded)">
<span class="command">
<strong>
ndbmtd
</strong>
</span>
</a>
to run in multithreaded
fashion.) Similarly, an
<a class="link" href="mysql-cluster-programs-ndbmtd.html" title="25.5.3 ndbmtd — The NDB Cluster Data Node Daemon (Multi-Threaded)">
<span class="command">
<strong>
ndbmtd
</strong>
</span>
</a>
binary can be
replaced with
<a class="link" href="mysql-cluster-programs-ndbd.html" title="25.5.1 ndbd — The NDB Cluster Data Node Daemon">
<span class="command">
<strong>
ndbd
</strong>
</span>
</a>
simply by stopping the
node and then starting
<a class="link" href="mysql-cluster-programs-ndbd.html" title="25.5.1 ndbd — The NDB Cluster Data Node Daemon">
<span class="command">
<strong>
ndbd
</strong>
</span>
</a>
in place of the
multithreaded binary. It is not necessary when switching between
the two to start the data node binary using
<a class="link" href="mysql-cluster-programs-ndbd.html#option_ndbd_initial">
<code class="option">
--initial
</code>
</a>
.
</p>
<p>
Using
<a class="link" href="mysql-cluster-programs-ndbmtd.html" title="25.5.3 ndbmtd — The NDB Cluster Data Node Daemon (Multi-Threaded)">
<span class="command">
<strong>
ndbmtd
</strong>
</span>
</a>
differs from using
<a class="link" href="mysql-cluster-programs-ndbd.html" title="25.5.1 ndbd — The NDB Cluster Data Node Daemon">
<span class="command">
<strong>
ndbd
</strong>
</span>
</a>
in two key respects:
</p>
<div class="orderedlist">
<ol class="orderedlist" type="1">
<li class="listitem">
<p>
Because
<a class="link" href="mysql-cluster-programs-ndbmtd.html" title="25.5.3 ndbmtd — The NDB Cluster Data Node Daemon (Multi-Threaded)">
<span class="command">
<strong>
ndbmtd
</strong>
</span>
</a>
runs by default in
single-threaded mode (that is, it behaves like
<a class="link" href="mysql-cluster-programs-ndbd.html" title="25.5.1 ndbd — The NDB Cluster Data Node Daemon">
<span class="command">
<strong>
ndbd
</strong>
</span>
</a>
), you must configure it to use
multiple threads. This can be done by setting an appropriate
value in the
<code class="filename">
config.ini
</code>
file for the
<a class="link" href="mysql-cluster-ndbd-definition.html#ndbparam-ndbmtd-maxnoofexecutionthreads">
<code class="literal">
MaxNoOfExecutionThreads
</code>
</a>
configuration parameter or the
<a class="link" href="mysql-cluster-ndbd-definition.html#ndbparam-ndbmtd-threadconfig">
<code class="literal">
ThreadConfig
</code>
</a>
configuration parameter. Using
<code class="literal">
MaxNoOfExecutionThreads
</code>
is simpler, but
<code class="literal">
ThreadConfig
</code>
offers more flexibility. For
more information about these configuration parameters and
their use, see
<a class="xref" href="mysql-cluster-ndbd-definition.html#mysql-cluster-ndbd-definition-ndbmtd-parameters" title="Multi-Threading Configuration Parameters (ndbmtd)">
Multi-Threading Configuration Parameters (ndbmtd)
</a>
.
</p>
</li>
<li class="listitem">
<p>
Trace files are generated by critical errors in
<a class="link" href="mysql-cluster-programs-ndbmtd.html" title="25.5.3 ndbmtd — The NDB Cluster Data Node Daemon (Multi-Threaded)">
<span class="command">
<strong>
ndbmtd
</strong>
</span>
</a>
processes in a somewhat different
fashion from how these are generated by
<a class="link" href="mysql-cluster-programs-ndbd.html" title="25.5.1 ndbd — The NDB Cluster Data Node Daemon">
<span class="command">
<strong>
ndbd
</strong>
</span>
</a>
failures. These differences are
discussed in more detail in the next few paragraphs.
</p>
</li>
</ol>
</div>
<a class="indexterm" name="idm46045107241600">
</a>
<a class="indexterm" name="idm46045107240112">
</a>
<a class="indexterm" name="idm46045107238624">
</a>
<a class="indexterm" name="idm46045107237136">
</a>
<a class="indexterm" name="idm46045107235648">
</a>
<p>
Like
<a class="link" href="mysql-cluster-programs-ndbd.html" title="25.5.1 ndbd — The NDB Cluster Data Node Daemon">
<span class="command">
<strong>
ndbd
</strong>
</span>
</a>
,
<a class="link" href="mysql-cluster-programs-ndbmtd.html" title="25.5.3 ndbmtd — The NDB Cluster Data Node Daemon (Multi-Threaded)">
<span class="command">
<strong>
ndbmtd
</strong>
</span>
</a>
generates a set of log files which are placed in the directory
specified by
<a class="link" href="mysql-cluster-ndbd-definition.html#ndbparam-ndbd-datadir">
<code class="literal">
DataDir
</code>
</a>
in
the
<code class="filename">
config.ini
</code>
configuration file. Except
for trace files, these are generated in the same way and have
the same names as those generated by
<a class="link" href="mysql-cluster-programs-ndbd.html" title="25.5.1 ndbd — The NDB Cluster Data Node Daemon">
<span class="command">
<strong>
ndbd
</strong>
</span>
</a>
.
</p>
<p>
In the event of a critical error,
<a class="link" href="mysql-cluster-programs-ndbmtd.html" title="25.5.3 ndbmtd — The NDB Cluster Data Node Daemon (Multi-Threaded)">
<span class="command">
<strong>
ndbmtd
</strong>
</span>
</a>
generates trace files describing what happened just prior to the
error' occurrence. These files, which can be found in the
data node's
<a class="link" href="mysql-cluster-ndbd-definition.html#ndbparam-ndbd-datadir">
<code class="literal">
DataDir
</code>
</a>
, are useful for
analysis of problems by the NDB Cluster Development and Support
teams. One trace file is generated for each
<a class="link" href="mysql-cluster-programs-ndbmtd.html" title="25.5.3 ndbmtd — The NDB Cluster Data Node Daemon (Multi-Threaded)">
<span class="command">
<strong>
ndbmtd
</strong>
</span>
</a>
thread. The names of these files have
the following pattern:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-terminal"><div class="docs-select-all right" id="sa94918804"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-terminal">ndb_<em class="replaceable">node_id</em>_trace<span class="token punctuation">.</span>log<span class="token punctuation">.</span><em class="replaceable">trace_id</em>_t<em class="replaceable">thread_id</em><span class="token punctuation">,</span></code></pre>
</div>
<p>
In this pattern,
<em class="replaceable">
<code>
node_id
</code>
</em>
stands for
the data node's unique node ID in the cluster,
<em class="replaceable">
<code>
trace_id
</code>
</em>
is a trace sequence number,
and
<em class="replaceable">
<code>
thread_id
</code>
</em>
is the thread ID. For
example, in the event of the failure of an
<a class="link" href="mysql-cluster-programs-ndbmtd.html" title="25.5.3 ndbmtd — The NDB Cluster Data Node Daemon (Multi-Threaded)">
<span class="command">
<strong>
ndbmtd
</strong>
</span>
</a>
process running as an NDB Cluster data
node having the node ID 3 and with
<a class="link" href="mysql-cluster-ndbd-definition.html#ndbparam-ndbmtd-maxnoofexecutionthreads">
<code class="literal">
MaxNoOfExecutionThreads
</code>
</a>
equal to 4, four trace files are generated in the data
node's data directory. If the is the first time this node
has failed, then these files are named
<code class="filename">
ndb_3_trace.log.1_t1
</code>
,
<code class="filename">
ndb_3_trace.log.1_t2
</code>
,
<code class="filename">
ndb_3_trace.log.1_t3
</code>
, and
<code class="filename">
ndb_3_trace.log.1_t4
</code>
. Internally, these
trace files follow the same format as
<a class="link" href="mysql-cluster-programs-ndbd.html" title="25.5.1 ndbd — The NDB Cluster Data Node Daemon">
<span class="command">
<strong>
ndbd
</strong>
</span>
</a>
trace files.
</p>
<p>
The
<a class="link" href="mysql-cluster-programs-ndbd.html" title="25.5.1 ndbd — The NDB Cluster Data Node Daemon">
<span class="command">
<strong>
ndbd
</strong>
</span>
</a>
exit codes and messages that are
generated when a data node process shuts down prematurely are
also used by
<a class="link" href="mysql-cluster-programs-ndbmtd.html" title="25.5.3 ndbmtd — The NDB Cluster Data Node Daemon (Multi-Threaded)">
<span class="command">
<strong>
ndbmtd
</strong>
</span>
</a>
. See
<a class="ulink" href="/doc/ndb-internals/en/ndb-node-error-messages.html" target="_top">
Data Node Error Messages
</a>
, for a listing of
these.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
It is possible to use
<a class="link" href="mysql-cluster-programs-ndbd.html" title="25.5.1 ndbd — The NDB Cluster Data Node Daemon">
<span class="command">
<strong>
ndbd
</strong>
</span>
</a>
and
<a class="link" href="mysql-cluster-programs-ndbmtd.html" title="25.5.3 ndbmtd — The NDB Cluster Data Node Daemon (Multi-Threaded)">
<span class="command">
<strong>
ndbmtd
</strong>
</span>
</a>
concurrently on different data nodes
in the same NDB Cluster. However, such configurations have not
been tested extensively; thus, we cannot recommend doing so in
a production setting at this time.
</p>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/compiling-for-debugging.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="compiling-for-debugging">
</a>
7.9.1.1 Compiling MySQL for Debugging
</h4>
</div>
</div>
</div>
<p>
If you have some very specific problem, you can always try to
debug MySQL. To do this you must configure MySQL with the
<a class="link" href="source-configuration-options.html#option_cmake_with_debug">
<code class="option">
-DWITH_DEBUG=1
</code>
</a>
option. You can
check whether MySQL was compiled with debugging by doing:
<a class="link" href="mysqld.html" title="6.3.1 mysqld — The MySQL Server">
<span class="command">
<strong>
mysqld --help
</strong>
</span>
</a>
. If the
<a class="link" href="server-options.html#option_mysqld_debug">
<code class="option">
--debug
</code>
</a>
flag is listed with the
options then you have debugging enabled.
<a class="link" href="mysqladmin.html" title="6.5.2 mysqladmin — A MySQL Server Administration Program">
<span class="command">
<strong>
mysqladmin
ver
</strong>
</span>
</a>
also lists the
<a class="link" href="mysqld.html" title="6.3.1 mysqld — The MySQL Server">
<span class="command">
<strong>
mysqld
</strong>
</span>
</a>
version
as
<a class="link" href="mysql.html" title="6.5.1 mysql — The MySQL Command-Line Client">
<span class="command">
<strong>
mysql ... --debug
</strong>
</span>
</a>
in this case.
</p>
<p>
If
<a class="link" href="mysqld.html" title="6.3.1 mysqld — The MySQL Server">
<span class="command">
<strong>
mysqld
</strong>
</span>
</a>
stops crashing when you configure
it with the
<a class="link" href="source-configuration-options.html#option_cmake_with_debug">
<code class="option">
-DWITH_DEBUG=1
</code>
</a>
CMake
option, you probably have found a compiler bug or a timing bug
within MySQL. In this case, you can try to add
<code class="option">
-g
</code>
using the
<a class="link" href="source-configuration-options.html#option_cmake_cmake_c_flags">
<code class="option">
CMAKE_C_FLAGS
</code>
</a>
and
<a class="link" href="source-configuration-options.html#option_cmake_cmake_cxx_flags">
<code class="option">
CMAKE_CXX_FLAGS
</code>
</a>
CMake options and
not use
<a class="link" href="source-configuration-options.html#option_cmake_with_debug">
<code class="option">
-DWITH_DEBUG=1
</code>
</a>
. If
<a class="link" href="mysqld.html" title="6.3.1 mysqld — The MySQL Server">
<span class="command">
<strong>
mysqld
</strong>
</span>
</a>
dies, you can at least attach to it
with
<span class="command">
<strong>
gdb
</strong>
</span>
or use
<span class="command">
<strong>
gdb
</strong>
</span>
on the
core file to find out what happened.
</p>
<p>
When you configure MySQL for debugging you automatically enable
a lot of extra safety check functions that monitor the health of
<a class="link" href="mysqld.html" title="6.3.1 mysqld — The MySQL Server">
<span class="command">
<strong>
mysqld
</strong>
</span>
</a>
. If they find something
<span class="quote">
“
<span class="quote">
unexpected,
</span>
”
</span>
an entry is written to
<code class="literal">
stderr
</code>
, which
<a class="link" href="mysqld-safe.html" title="6.3.2 mysqld_safe — MySQL Server Startup Script">
<span class="command">
<strong>
mysqld_safe
</strong>
</span>
</a>
directs to the error log! This also means that if you are having
some unexpected problems with MySQL and are using a source
distribution, the first thing you should do is to configure
MySQL for debugging. If you believe that you have found a bug,
please use the instructions at
<a class="xref" href="bug-reports.html" title="1.6 How to Report Bugs or Problems">
Section 1.6, “How to Report Bugs or Problems”
</a>
.
</p>
<p>
In the Windows MySQL distribution,
<code class="literal">
mysqld.exe
</code>
is by default compiled with support for trace files.
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/replication-howto-masterbaseconfig.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="replication-howto-masterbaseconfig">
</a>
19.1.2.1 Setting the Replication Source Configuration
</h4>
</div>
</div>
</div>
<p>
To configure a source to use binary log file position based
replication, you must ensure that binary logging is enabled, and
establish a unique server ID.
</p>
<p>
Each server within a replication topology must be configured
with a unique server ID, which you can specify using the
<a class="link" href="replication-options.html#sysvar_server_id">
<code class="literal">
server_id
</code>
</a>
system variable. This
server ID is used to identify individual servers within the
replication topology, and must be a positive integer between 1
and (2
<sup>
32
</sup>
)−1. The default
<a class="link" href="replication-options.html#sysvar_server_id">
<code class="literal">
server_id
</code>
</a>
value is 1; you can
change this at runtime by issuing a statement like this one:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa20217184"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">SET</span> <span class="token keyword">GLOBAL</span> server_id <span class="token operator">=</span> <span class="token number">2</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
Organization and selection of the server IDs is arbitrary, as
long as each server ID is different from every other server ID
in use by any other server in the replication topology. Note
that if a value of 0 was set previously for the server ID, you
must restart the server to initialize the source with your new
nonzero server ID. Otherwise, a server restart is not needed
when you change the server ID, unless you make other
configuration changes that require it.
</p>
<p>
Binary logging is required on the source because the binary log
is the basis for replicating changes from the source to its
replicas. Binary logging is enabled by default (the
<a class="link" href="replication-options-binary-log.html#sysvar_log_bin">
<code class="literal">
log_bin
</code>
</a>
system variable is set
to ON). The
<a class="link" href="replication-options-binary-log.html#option_mysqld_log-bin">
<code class="option">
--log-bin
</code>
</a>
option
tells the server what base name to use for binary log files. It
is recommended that you specify this option to give the binary
log files a non-default base name, so that if the host name
changes, you can easily continue to use the same binary log file
names (see
<a class="xref" href="known-issues.html" title="B.3.7 Known Issues in MySQL">
Section B.3.7, “Known Issues in MySQL”
</a>
). If binary logging
was previously disabled on the source using the
<a class="link" href="replication-options-binary-log.html#option_mysqld_log-bin">
<code class="option">
--skip-log-bin
</code>
</a>
option, you must restart the server without this option to
enable it.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
The following options also have an impact on the source:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
For the greatest possible durability and consistency in a
replication setup using
<a class="link" href="innodb-storage-engine.html" title="Chapter 17 The InnoDB Storage Engine">
<code class="literal">
InnoDB
</code>
</a>
with transactions, you
should use
<code class="literal">
innodb_flush_log_at_trx_commit=1
</code>
and
<code class="literal">
sync_binlog=1
</code>
in the source's
<code class="filename">
my.cnf
</code>
file.
</p>
</li>
<li class="listitem">
<p>
Ensure that the
<a class="link" href="server-system-variables.html#sysvar_skip_networking">
<code class="literal">
skip_networking
</code>
</a>
system
variable is not enabled on the source. If networking has
been disabled, the replica cannot communicate with the
source and replication fails.
</p>
</li>
</ul>
</div>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/group-replication-performance-xcom-cache-increase.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="group-replication-performance-xcom-cache-increase">
</a>
20.7.6.1 Increasing the cache size
</h4>
</div>
</div>
</div>
<p>
If a member is absent for a period that is not long enough for
it to be expelled from the group, it can reconnect and start
participating in the group again by retrieving missed
transactions from another member's XCom message cache. However,
if the transactions that happened during the member's absence
have been deleted from the other members' XCom message caches
because their maximum size limit was reached, the member cannot
reconnect in this way.
</p>
<p>
Group Replication's Group Communication System (GCS) alerts you,
by a warning message, when a message that is likely to be needed
for recovery by a member that is currently unreachable is
removed from the message cache. This warning message is logged
on all the active group members (only once for each unreachable
member). Although the group members cannot know for sure what
message was the last message seen by the unreachable member, the
warning message indicates that the cache size might not be
sufficient to support your chosen waiting period before a member
is expelled.
</p>
<p>
In this situation, consider increasing the
<a class="link" href="group-replication-system-variables.html#sysvar_group_replication_message_cache_size">
<code class="literal">
group_replication_message_cache_size
</code>
</a>
limit with reference to the expected volume of messages in the
time period specified by the
<a class="link" href="group-replication-system-variables.html#sysvar_group_replication_member_expel_timeout">
<code class="literal">
group_replication_member_expel_timeout
</code>
</a>
system variable plus the 5-second detection period, so that the
cache contains all the missed messages required for members to
return successfully. You can also consider increasing the cache
size limit temporarily if you expect a member to become
unreachable for an unusual period of time.
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/mysql-cluster-limitations-performance.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="mysql-cluster-limitations-performance">
</a>
25.2.7.7 Limitations Relating to Performance in NDB Cluster
</h4>
</div>
</div>
</div>
<a class="indexterm" name="idm46045123237488">
</a>
<p>
The following performance issues are specific to or especially
pronounced in NDB Cluster:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<b>
Range scans.
</b>
There are query performance issues due to sequential
access to the
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDB
</code>
</a>
storage
engine; it is also relatively more expensive to do many
range scans than it is with either
<code class="literal">
MyISAM
</code>
or
<code class="literal">
InnoDB
</code>
.
</p>
</li>
<li class="listitem">
<p>
<b>
Reliability of Records in range.
</b>
The
<code class="literal">
Records in range
</code>
statistic is
available but is not completely tested or officially
supported. This may result in nonoptimal query plans in
some cases. If necessary, you can employ
<code class="literal">
USE
INDEX
</code>
or
<code class="literal">
FORCE INDEX
</code>
to alter
the execution plan. See
<a class="xref" href="index-hints.html" title="10.9.4 Index Hints">
Section 10.9.4, “Index Hints”
</a>
, for
more information on how to do this.
</p>
</li>
<li class="listitem">
<p>
<b>
Unique hash indexes.
</b>
Unique hash indexes created with
<code class="literal">
USING
HASH
</code>
cannot be used for accessing a table if
<code class="literal">
NULL
</code>
is given as part of the key.
</p>
</li>
</ul>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/binary-log-formats.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="binary-log-formats">
</a>
7.4.4.1 Binary Logging Formats
</h4>
</div>
</div>
</div>
<p>
The server uses several logging formats to record information in
the binary log:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
Replication capabilities in MySQL originally were based on
propagation of SQL statements from source to replica. This
is called
<span class="emphasis">
<em>
statement-based logging
</em>
</span>
. You
can cause this format to be used by starting the server with
<a class="link" href="replication-options-binary-log.html#sysvar_binlog_format">
<code class="option">
--binlog-format=STATEMENT
</code>
</a>
.
</p>
</li>
<li class="listitem">
<p>
In
<span class="emphasis">
<em>
row-based logging
</em>
</span>
(the default), the
source writes events to the binary log that indicate how
individual table rows are affected. You can cause the server
to use row-based logging by starting it with
<a class="link" href="replication-options-binary-log.html#sysvar_binlog_format">
<code class="option">
--binlog-format=ROW
</code>
</a>
.
</p>
</li>
<li class="listitem">
<p>
A third option is also available:
<span class="emphasis">
<em>
mixed
logging
</em>
</span>
. With mixed logging, statement-based
logging is used by default, but the logging mode switches
automatically to row-based in certain cases as described
below. You can cause MySQL to use mixed logging explicitly
by starting
<a class="link" href="mysqld.html" title="6.3.1 mysqld — The MySQL Server">
<span class="command">
<strong>
mysqld
</strong>
</span>
</a>
with the option
<a class="link" href="replication-options-binary-log.html#sysvar_binlog_format">
<code class="option">
--binlog-format=MIXED
</code>
</a>
.
</p>
</li>
</ul>
</div>
<p>
The logging format can also be set or limited by the storage
engine being used. This helps to eliminate issues when
replicating certain statements between a source and replica
which are using different storage engines.
</p>
<p>
With statement-based replication, there may be issues with
replicating nondeterministic statements. In deciding whether or
not a given statement is safe for statement-based replication,
MySQL determines whether it can guarantee that the statement can
be replicated using statement-based logging. If MySQL cannot
make this guarantee, it marks the statement as potentially
unreliable and issues the warning,
<span class="errortext">
Statement may not
be safe to log in statement format
</span>
.
</p>
<p>
You can avoid these issues by using MySQL's row-based
replication instead.
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/charset-connection.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h2 class="title">
<a name="charset-connection">
</a>
12.4 Connection Character Sets and Collations
</h2>
</div>
</div>
</div>
<a class="indexterm" name="idm46045217500720">
</a>
<a class="indexterm" name="idm46045217499296">
</a>
<p>
A
<span class="quote">
“
<span class="quote">
connection
</span>
”
</span>
is what a client program makes when it
connects to the server, to begin a session within which it
interacts with the server. The client sends SQL statements, such
as queries, over the session connection. The server sends
responses, such as result sets or error messages, over the
connection back to the client.
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<a class="xref" href="charset-connection.html#charset-connection-system-variables" title="Connection Character Set and Collation System Variables">
Connection Character Set and Collation System Variables
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="charset-connection.html#charset-connection-impermissible-client-charset" title="Impermissible Client Character Sets">
Impermissible Client Character Sets
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="charset-connection.html#charset-connection-client-configuration" title="Client Program Connection Character Set Configuration">
Client Program Connection Character Set Configuration
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="charset-connection.html#charset-connection-sql-statements" title="SQL Statements for Connection Character Set Configuration">
SQL Statements for Connection Character Set Configuration
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="charset-connection.html#charset-connection-error-handling" title="Connection Character Set Error Handling">
Connection Character Set Error Handling
</a>
</p>
</li>
</ul>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h3 class="title">
<a name="charset-connection-system-variables">
</a>
Connection Character Set and Collation System Variables
</h3>
</div>
</div>
</div>
<p>
Several character set and collation system variables relate to a
client's interaction with the server. Some of these have been
mentioned in earlier sections:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
The
<a class="link" href="server-system-variables.html#sysvar_character_set_server">
<code class="literal">
character_set_server
</code>
</a>
and
<a class="link" href="server-system-variables.html#sysvar_collation_server">
<code class="literal">
collation_server
</code>
</a>
system
variables indicate the server character set and collation.
See
<a class="xref" href="charset-server.html" title="12.3.2 Server Character Set and Collation">
Section 12.3.2, “Server Character Set and Collation”
</a>
.
</p>
</li>
<li class="listitem">
<p>
The
<a class="link" href="server-system-variables.html#sysvar_character_set_database">
<code class="literal">
character_set_database
</code>
</a>
and
<a class="link" href="server-system-variables.html#sysvar_collation_database">
<code class="literal">
collation_database
</code>
</a>
system variables indicate the character set and collation of
the default database. See
<a class="xref" href="charset-database.html" title="12.3.3 Database Character Set and Collation">
Section 12.3.3, “Database Character Set and Collation”
</a>
.
</p>
</li>
</ul>
</div>
<p>
Additional character set and collation system variables are
involved in handling traffic for the connection between a client
and the server. Every client has session-specific
connection-related character set and collation system variables.
These session system variable values are initialized at connect
time, but can be changed within the session.
</p>
<p>
Several questions about character set and collation handling for
client connections can be answered in terms of system variables:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
What character set are statements in when they leave the
client?
</p>
<p>
The server takes the
<a class="link" href="server-system-variables.html#sysvar_character_set_client">
<code class="literal">
character_set_client
</code>
</a>
system
variable to be the character set in which statements are
sent by the client.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
Some character sets cannot be used as the client character
set. See
<a class="xref" href="charset-connection.html#charset-connection-impermissible-client-charset" title="Impermissible Client Character Sets">
Impermissible Client Character Sets
</a>
.
</p>
</div>
</li>
<li class="listitem">
<p>
What character set should the server translate statements to
after receiving them?
</p>
<p>
To determine this, the server uses the
<a class="link" href="server-system-variables.html#sysvar_character_set_connection">
<code class="literal">
character_set_connection
</code>
</a>
and
<a class="link" href="server-system-variables.html#sysvar_collation_connection">
<code class="literal">
collation_connection
</code>
</a>
system variables:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<p>
The server converts statements sent by the client from
<a class="link" href="server-system-variables.html#sysvar_character_set_client">
<code class="literal">
character_set_client
</code>
</a>
to
<a class="link" href="server-system-variables.html#sysvar_character_set_connection">
<code class="literal">
character_set_connection
</code>
</a>
.
Exception: For string literals that have an introducer
such as
<code class="literal">
_utf8mb4
</code>
or
<code class="literal">
_latin2
</code>
, the introducer determines
the character set. See
<a class="xref" href="charset-introducer.html" title="12.3.8 Character Set Introducers">
Section 12.3.8, “Character Set Introducers”
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a class="link" href="server-system-variables.html#sysvar_collation_connection">
<code class="literal">
collation_connection
</code>
</a>
is
important for comparisons of literal strings. For
comparisons of strings with column values,
<a class="link" href="server-system-variables.html#sysvar_collation_connection">
<code class="literal">
collation_connection
</code>
</a>
does not matter because columns have their own
collation, which has a higher collation precedence (see
<a class="xref" href="charset-collation-coercibility.html" title="12.8.4 Collation Coercibility in Expressions">
Section 12.8.4, “Collation Coercibility in Expressions”
</a>
).
</p>
</li>
</ul>
</div>
</li>
<li class="listitem">
<p>
What character set should the server translate query results
to before shipping them back to the client?
</p>
<p>
The
<a class="link" href="server-system-variables.html#sysvar_character_set_results">
<code class="literal">
character_set_results
</code>
</a>
system variable indicates the character set in which the
server returns query results to the client. This includes
result data such as column values, result metadata such as
column names, and error messages.
</p>
<p>
To tell the server to perform no conversion of result sets
or error messages, set
<a class="link" href="server-system-variables.html#sysvar_character_set_results">
<code class="literal">
character_set_results
</code>
</a>
to
<code class="literal">
NULL
</code>
or
<code class="literal">
binary
</code>
:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa23548271"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">SET</span> character_set_results <span class="token operator">=</span> <span class="token boolean">NULL</span><span class="token punctuation">;</span>
<span class="token keyword">SET</span> character_set_results <span class="token operator">=</span> <span class="token datatype">binary</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
For more information about character sets and error
messages, see
<a class="xref" href="charset-errors.html" title="12.6 Error Message Character Set">
Section 12.6, “Error Message Character Set”
</a>
.
</p>
</li>
</ul>
</div>
<p>
To see the values of the character set and collation system
variables that apply to the current session, use this statement:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa29655615"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> performance_schema<span class="token punctuation">.</span>session_variables
<span class="token keyword">WHERE</span> VARIABLE_NAME <span class="token keyword">IN</span> <span class="token punctuation">(</span>
<span class="token string">'character_set_client'</span><span class="token punctuation">,</span> <span class="token string">'character_set_connection'</span><span class="token punctuation">,</span>
<span class="token string">'character_set_results'</span><span class="token punctuation">,</span> <span class="token string">'collation_connection'</span>
<span class="token punctuation">)</span> <span class="token keyword">ORDER</span> <span class="token keyword">BY</span> VARIABLE_NAME<span class="token punctuation">;</span></code></pre>
</div>
<p>
The following simpler statements also display the connection
variables, but include other related variables as well. They can
be useful to see
<span class="emphasis">
<em>
all
</em>
</span>
character set and
collation system variables:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa72365866"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">SHOW</span> <span class="token keyword">SESSION</span> <span class="token keyword">VARIABLES</span> <span class="token operator">LIKE</span> <span class="token string">'character\_set\_%'</span><span class="token punctuation">;</span>
<span class="token keyword">SHOW</span> <span class="token keyword">SESSION</span> <span class="token keyword">VARIABLES</span> <span class="token operator">LIKE</span> <span class="token string">'collation\_%'</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
Clients can fine-tune the settings for these variables, or
depend on the defaults (in which case, you can skip the rest of
this section). If you do not use the defaults, you must change
the character settings
<span class="emphasis">
<em>
for each connection to the
server
</em>
</span>
.
</p>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h3 class="title">
<a name="charset-connection-impermissible-client-charset">
</a>
Impermissible Client Character Sets
</h3>
</div>
</div>
</div>
<a class="indexterm" name="idm46045217445920">
</a>
<a class="indexterm" name="idm46045217444432">
</a>
<a class="indexterm" name="idm46045217442944">
</a>
<a class="indexterm" name="idm46045217441456">
</a>
<p>
The
<a class="link" href="server-system-variables.html#sysvar_character_set_client">
<code class="literal">
character_set_client
</code>
</a>
system
variable cannot be set to certain character sets:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-simple"><div class="docs-select-all right" id="sa53895539"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-simple">ucs2
utf16
utf16le
utf32</code></pre>
</div>
<p>
Attempting to use any of those character sets as the client
character set produces an error:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa59988269"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SET</span> character_set_client <span class="token operator">=</span> <span class="token string">'ucs2'</span><span class="token punctuation">;</span>
<span class="token output">ERROR 1231 (42000)<span class="token punctuation">:</span> Variable 'character_set_client'
can't be set to the value of 'ucs2'</span></code></pre>
</div>
<p>
The same error occurs if any of those character sets are used in
the following contexts, all of which result in an attempt to set
<a class="link" href="server-system-variables.html#sysvar_character_set_client">
<code class="literal">
character_set_client
</code>
</a>
to the
named character set:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
The
<a class="link" href="mysql-command-options.html#option_mysql_default-character-set">
<code class="option">
--default-character-set=
<em class="replaceable">
<code>
charset_name
</code>
</em>
</code>
</a>
command option used by MySQL client programs such as
<a class="link" href="mysql.html" title="6.5.1 mysql — The MySQL Command-Line Client">
<span class="command">
<strong>
mysql
</strong>
</span>
</a>
and
<a class="link" href="mysqladmin.html" title="6.5.2 mysqladmin — A MySQL Server Administration Program">
<span class="command">
<strong>
mysqladmin
</strong>
</span>
</a>
.
</p>
</li>
<li class="listitem">
<p>
The
<a class="link" href="set-names.html" title="15.7.6.3 SET NAMES Statement">
<code class="literal">
SET NAMES
'
<em class="replaceable">
<code>
charset_name
</code>
</em>
'
</code>
</a>
statement.
</p>
</li>
<li class="listitem">
<p>
The
<a class="link" href="set-character-set.html" title="15.7.6.2 SET CHARACTER SET Statement">
<code class="literal">
SET
CHARACTER SET
'
<em class="replaceable">
<code>
charset_name
</code>
</em>
'
</code>
</a>
statement.
</p>
</li>
</ul>
</div>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h3 class="title">
<a name="charset-connection-client-configuration">
</a>
Client Program Connection Character Set Configuration
</h3>
</div>
</div>
</div>
<p>
When a client connects to the server, it indicates which
character set it wants to use for communication with the server.
(Actually, the client indicates the default collation for that
character set, from which the server can determine the character
set.) The server uses this information to set the
<a class="link" href="server-system-variables.html#sysvar_character_set_client">
<code class="literal">
character_set_client
</code>
</a>
,
<a class="link" href="server-system-variables.html#sysvar_character_set_results">
<code class="literal">
character_set_results
</code>
</a>
,
<a class="link" href="server-system-variables.html#sysvar_character_set_connection">
<code class="literal">
character_set_connection
</code>
</a>
system
variables to the character set, and
<a class="link" href="server-system-variables.html#sysvar_collation_connection">
<code class="literal">
collation_connection
</code>
</a>
to the
character set default collation. In effect, the server performs
the equivalent of a
<a class="link" href="set-names.html" title="15.7.6.3 SET NAMES Statement">
<code class="literal">
SET NAMES
</code>
</a>
operation.
</p>
<p>
If the server does not support the requested character set or
collation, it falls back to using the server character set and
collation to configure the connection. For additional detail
about this fallback behavior, see
<a class="xref" href="charset-connection.html#charset-connection-error-handling" title="Connection Character Set Error Handling">
Connection Character Set Error Handling
</a>
.
</p>
<p>
The
<a class="link" href="mysql.html" title="6.5.1 mysql — The MySQL Command-Line Client">
<span class="command">
<strong>
mysql
</strong>
</span>
</a>
,
<a class="link" href="mysqladmin.html" title="6.5.2 mysqladmin — A MySQL Server Administration Program">
<span class="command">
<strong>
mysqladmin
</strong>
</span>
</a>
,
<a class="link" href="mysqlcheck.html" title="6.5.3 mysqlcheck — A Table Maintenance Program">
<span class="command">
<strong>
mysqlcheck
</strong>
</span>
</a>
,
<a class="link" href="mysqlimport.html" title="6.5.5 mysqlimport — A Data Import Program">
<span class="command">
<strong>
mysqlimport
</strong>
</span>
</a>
,
and
<a class="link" href="mysqlshow.html" title="6.5.6 mysqlshow — Display Database, Table, and Column Information">
<span class="command">
<strong>
mysqlshow
</strong>
</span>
</a>
client programs determine the
default character set to use as follows:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
In the absence of other information, each client uses the
compiled-in default character set, usually
<code class="literal">
utf8mb4
</code>
.
</p>
</li>
<li class="listitem">
<p>
Each client can autodetect which character set to use based
on the operating system setting, such as the value of the
<code class="literal">
LANG
</code>
or
<code class="literal">
LC_ALL
</code>
locale
environment variable on Unix systems or the code page
setting on Windows systems. For systems on which the locale
is available from the OS, the client uses it to set the
default character set rather than using the compiled-in
default. For example, setting
<code class="literal">
LANG
</code>
to
<code class="literal">
ru_RU.KOI8-R
</code>
causes the
<code class="literal">
koi8r
</code>
character set to be used. Thus,
users can configure the locale in their environment for use
by MySQL clients.
</p>
<p>
The OS character set is mapped to the closest MySQL
character set if there is no exact match. If the client does
not support the matching character set, it uses the
compiled-in default. For example,
<code class="literal">
utf8
</code>
and
<code class="literal">
utf-8
</code>
map to
<code class="literal">
utf8mb4
</code>
, and
<code class="literal">
ucs2
</code>
is
not supported as a connection character set, so it maps to
the compiled-in default.
</p>
<p>
C applications can use character set autodetection based on
the OS setting by invoking
<a class="ulink" href="/doc/c-api/8.4/en/mysql-options.html" target="_top">
<code class="literal">
mysql_options()
</code>
</a>
as follows
before connecting to the server:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-c"><div class="docs-select-all right" id="sa94643175"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-c"><span class="token function">mysql_options</span><span class="token punctuation">(</span>mysql<span class="token punctuation">,</span>
MYSQL_SET_CHARSET_NAME<span class="token punctuation">,</span>
MYSQL_AUTODETECT_CHARSET_NAME<span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
</li>
<li class="listitem">
<p>
Each client supports a
<a class="link" href="mysql-command-options.html#option_mysql_default-character-set">
<code class="option">
--default-character-set
</code>
</a>
option, which enables users to specify the character set
explicitly to override whatever default the client otherwise
determines.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
Some character sets cannot be used as the client character
set. Attempting to use them with
<a class="link" href="mysql-command-options.html#option_mysql_default-character-set">
<code class="option">
--default-character-set
</code>
</a>
produces an error. See
<a class="xref" href="charset-connection.html#charset-connection-impermissible-client-charset" title="Impermissible Client Character Sets">
Impermissible Client Character Sets
</a>
.
</p>
</div>
</li>
</ul>
</div>
<p>
With the
<a class="link" href="mysql.html" title="6.5.1 mysql — The MySQL Command-Line Client">
<span class="command">
<strong>
mysql
</strong>
</span>
</a>
client, to use a character set
different from the default, you could explicitly execute a
<a class="link" href="set-names.html" title="15.7.6.3 SET NAMES Statement">
<code class="literal">
SET NAMES
</code>
</a>
statement every time
you connect to the server (see
<a class="xref" href="charset-connection.html#charset-connection-client-configuration" title="Client Program Connection Character Set Configuration">
Client Program Connection Character Set Configuration
</a>
). To
accomplish the same result more easily, specify the character
set in your option file. For example, the following option file
setting changes the three connection-related character set
system variables set to
<code class="literal">
koi8r
</code>
each time you
invoke
<a class="link" href="mysql.html" title="6.5.1 mysql — The MySQL Command-Line Client">
<span class="command">
<strong>
mysql
</strong>
</span>
</a>
:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-ini"><div class="docs-select-all right" id="sa58596468"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-ini"><span class="token selector">[mysql]</span>
<span class="token constant">default-character-set</span><span class="token attr-value"><span class="token punctuation">=</span>koi8r</span></code></pre>
</div>
<p>
If you are using the
<a class="link" href="mysql.html" title="6.5.1 mysql — The MySQL Command-Line Client">
<span class="command">
<strong>
mysql
</strong>
</span>
</a>
client with
auto-reconnect enabled (which is not recommended), it is
preferable to use the
<code class="literal">
charset
</code>
command rather
than
<a class="link" href="set-names.html" title="15.7.6.3 SET NAMES Statement">
<code class="literal">
SET NAMES
</code>
</a>
. For example:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa65618298"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">charset</span> koi8r
<span class="token keyword">Charset</span> <span class="token keyword">changed</span></code></pre>
</div>
<p>
The
<code class="literal">
charset
</code>
command issues a
<a class="link" href="set-names.html" title="15.7.6.3 SET NAMES Statement">
<code class="literal">
SET NAMES
</code>
</a>
statement, and also
changes the default character set that
<a class="link" href="mysql.html" title="6.5.1 mysql — The MySQL Command-Line Client">
<span class="command">
<strong>
mysql
</strong>
</span>
</a>
uses when it reconnects after the connection has dropped.
</p>
<p>
When configuration client programs, you must also consider the
environment within which they execute. See
<a class="xref" href="charset-applications.html" title="12.5 Configuring Application Character Set and Collation">
Section 12.5, “Configuring Application Character Set and Collation”
</a>
.
</p>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h3 class="title">
<a name="charset-connection-sql-statements">
</a>
SQL Statements for Connection Character Set Configuration
</h3>
</div>
</div>
</div>
<p>
After a connection has been established, clients can change the
character set and collation system variables for the current
session. These variables can be changed individually using
<a class="link" href="set-statement.html" title="15.7.6 SET Statements">
<code class="literal">
SET
</code>
</a>
statements, but two more convenient statements affect the
connection-related character set system variables as a group:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<code class="literal">
SET NAMES '
<em class="replaceable">
<code>
charset_name
</code>
</em>
'
[COLLATE
'
<em class="replaceable">
<code>
collation_name
</code>
</em>
']
</code>
</p>
<p>
<a class="link" href="set-names.html" title="15.7.6.3 SET NAMES Statement">
<code class="literal">
SET NAMES
</code>
</a>
indicates what
character set the client uses to send SQL statements to the
server. Thus,
<a class="link" href="set-names.html" title="15.7.6.3 SET NAMES Statement">
<code class="literal">
SET
NAMES 'cp1251'
</code>
</a>
tells the server,
<span class="quote">
“
<span class="quote">
future
incoming messages from this client are in character set
<code class="literal">
cp1251
</code>
.
</span>
”
</span>
It also specifies the
character set that the server should use for sending results
back to the client. (For example, it indicates what
character set to use for column values if you use a
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT
</code>
</a>
statement that
produces a result set.)
</p>
<p>
A
<a class="link" href="set-names.html" title="15.7.6.3 SET NAMES Statement">
<code class="literal">
SET NAMES
'
<em class="replaceable">
<code>
charset_name
</code>
</em>
'
</code>
</a>
statement is equivalent to these three statements:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa36956650"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">SET</span> character_set_client <span class="token operator">=</span> <em class="replaceable">charset_name</em><span class="token punctuation">;</span>
<span class="token keyword">SET</span> character_set_results <span class="token operator">=</span> <em class="replaceable">charset_name</em><span class="token punctuation">;</span>
<span class="token keyword">SET</span> character_set_connection <span class="token operator">=</span> <em class="replaceable">charset_name</em><span class="token punctuation">;</span></code></pre>
</div>
<p>
Setting
<a class="link" href="server-system-variables.html#sysvar_character_set_connection">
<code class="literal">
character_set_connection
</code>
</a>
to
<em class="replaceable">
<code>
charset_name
</code>
</em>
also implicitly sets
<a class="link" href="server-system-variables.html#sysvar_collation_connection">
<code class="literal">
collation_connection
</code>
</a>
to the
default collation for
<em class="replaceable">
<code>
charset_name
</code>
</em>
. It is unnecessary
to set that collation explicitly. To specify a particular
collation to use for
<a class="link" href="server-system-variables.html#sysvar_collation_connection">
<code class="literal">
collation_connection
</code>
</a>
, add a
<code class="literal">
COLLATE
</code>
clause:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa67500059"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">SET</span> <span class="token keyword">NAMES</span> <span class="token string">'<em class="replaceable">charset_name</em>'</span> <span class="token keyword">COLLATE</span> <span class="token string">'<em class="replaceable">collation_name</em>'</span></code></pre>
</div>
</li>
<li class="listitem">
<p>
<code class="literal">
SET CHARACTER SET
'
<em class="replaceable">
<code>
charset_name
</code>
</em>
</code>
'
</p>
<p>
<a class="link" href="set-character-set.html" title="15.7.6.2 SET CHARACTER SET Statement">
<code class="literal">
SET CHARACTER SET
</code>
</a>
is similar
to
<a class="link" href="set-names.html" title="15.7.6.3 SET NAMES Statement">
<code class="literal">
SET NAMES
</code>
</a>
but sets
<a class="link" href="server-system-variables.html#sysvar_character_set_connection">
<code class="literal">
character_set_connection
</code>
</a>
and
<a class="link" href="server-system-variables.html#sysvar_collation_connection">
<code class="literal">
collation_connection
</code>
</a>
to
<a class="link" href="server-system-variables.html#sysvar_character_set_database">
<code class="literal">
character_set_database
</code>
</a>
and
<a class="link" href="server-system-variables.html#sysvar_collation_database">
<code class="literal">
collation_database
</code>
</a>
(which,
as mentioned previously, indicate the character set and
collation of the default database).
</p>
<p>
A
<a class="link" href="set-character-set.html" title="15.7.6.2 SET CHARACTER SET Statement">
<code class="literal">
SET
CHARACTER SET
<em class="replaceable">
<code>
charset_name
</code>
</em>
</code>
</a>
statement
is equivalent to these three statements:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa7373368"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">SET</span> character_set_client <span class="token operator">=</span> <em class="replaceable">charset_name</em><span class="token punctuation">;</span>
<span class="token keyword">SET</span> character_set_results <span class="token operator">=</span> <em class="replaceable">charset_name</em><span class="token punctuation">;</span>
<span class="token keyword">SET</span> collation_connection <span class="token operator">=</span> <span class="token variable">@@collation_database</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
Setting
<a class="link" href="server-system-variables.html#sysvar_collation_connection">
<code class="literal">
collation_connection
</code>
</a>
also
implicitly sets
<a class="link" href="server-system-variables.html#sysvar_character_set_connection">
<code class="literal">
character_set_connection
</code>
</a>
to
the character set associated with the collation (equivalent
to executing
<code class="literal">
SET character_set_connection =
@@character_set_database
</code>
). It is unnecessary to
set
<a class="link" href="server-system-variables.html#sysvar_character_set_connection">
<code class="literal">
character_set_connection
</code>
</a>
explicitly.
</p>
</li>
</ul>
</div>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
Some character sets cannot be used as the client character
set. Attempting to use them with
<a class="link" href="set-names.html" title="15.7.6.3 SET NAMES Statement">
<code class="literal">
SET
NAMES
</code>
</a>
or
<a class="link" href="set-character-set.html" title="15.7.6.2 SET CHARACTER SET Statement">
<code class="literal">
SET CHARACTER
SET
</code>
</a>
produces an error. See
<a class="xref" href="charset-connection.html#charset-connection-impermissible-client-charset" title="Impermissible Client Character Sets">
Impermissible Client Character Sets
</a>
.
</p>
</div>
<p>
Example: Suppose that
<code class="literal">
column1
</code>
is defined as
<code class="literal">
CHAR(5) CHARACTER SET latin2
</code>
. If you do not
say
<a class="link" href="set-names.html" title="15.7.6.3 SET NAMES Statement">
<code class="literal">
SET NAMES
</code>
</a>
or
<a class="link" href="set-character-set.html" title="15.7.6.2 SET CHARACTER SET Statement">
<code class="literal">
SET CHARACTER SET
</code>
</a>
, then for
<code class="literal">
SELECT column1 FROM t
</code>
, the server sends back
all the values for
<code class="literal">
column1
</code>
using the
character set that the client specified when it connected. On
the other hand, if you say
<code class="literal">
SET NAMES 'latin1'
</code>
or
<code class="literal">
SET CHARACTER SET 'latin1'
</code>
before issuing
the
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT
</code>
</a>
statement, the server
converts the
<code class="literal">
latin2
</code>
values to
<code class="literal">
latin1
</code>
just before sending results back.
Conversion may be lossy for characters that are not in both
character sets.
</p>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h3 class="title">
<a name="charset-connection-error-handling">
</a>
Connection Character Set Error Handling
</h3>
</div>
</div>
</div>
<p>
Attempts to use an inappropriate connection character set or
collation can produce an error, or cause the server to fall back
to its default character set and collation for a given
connection. This section describes problems that can occur when
configuring the connection character set. These problems can
occur when establishing a connection or when changing the
character set within an established connection.
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<a class="xref" href="charset-connection.html#charset-connection-error-handling-connect-time" title="Connect-Time Error Handling">
Connect-Time Error Handling
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="charset-connection.html#charset-connection-error-handling-runtime" title="Runtime Error Handling">
Runtime Error Handling
</a>
</p>
</li>
</ul>
</div>
<h4>
<a name="charset-connection-error-handling-connect-time">
</a>
Connect-Time Error Handling
</h4>
<p>
Some character sets cannot be used as the client character set;
see
<a class="xref" href="charset-connection.html#charset-connection-impermissible-client-charset" title="Impermissible Client Character Sets">
Impermissible Client Character Sets
</a>
.
If you specify a character set that is valid but not permitted
as a client character set, the server returns an error:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-terminal"><div class="docs-select-all right" id="sa20658202"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-terminal"><span class="token prompt">$> </span><span class="token command">mysql</span> <span class="token constant">--default-character-set</span><span class="token attr-value"><span class="token punctuation">=</span>ucs2</span>
<span class="token output">ERROR 1231 (42000)<span class="token punctuation">:</span> Variable 'character_set_client' can't be set to
the value of 'ucs2'</span></code></pre>
</div>
<p>
If you specify a character set that the client does not
recognize, it produces an error:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-terminal"><div class="docs-select-all right" id="sa76698779"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-terminal"><span class="token prompt">$> </span><span class="token command">mysql</span> <span class="token constant">--default-character-set</span><span class="token attr-value"><span class="token punctuation">=</span>bogus</span>
mysql<span class="token punctuation">:</span> Character set <span class="token atrule">'bogus'</span> is not a compiled character set and is
not specified in the <span class="token atrule">'/usr/local/mysql/share/charsets/Index.xml'</span> file
<span class="token output">ERROR 2019 (HY000)<span class="token punctuation">:</span> Can't initialize character set bogus
(path<span class="token punctuation">:</span> /usr/local/mysql/share/charsets/)</span></code></pre>
</div>
<p>
If you specify a character set that the client recognizes but
the server does not, the server falls back to its default
character set and collation. Suppose that the server is
configured to use
<code class="literal">
latin1
</code>
and
<code class="literal">
latin1_swedish_ci
</code>
as its defaults, and that
it does not recognize
<code class="literal">
gb18030
</code>
as a valid
character set. A client that specifies
<a class="link" href="mysql-command-options.html#option_mysql_default-character-set">
<code class="option">
--default-character-set=gb18030
</code>
</a>
is
able to connect to the server, but the resulting character set
is not what the client wants:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa33799621"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SHOW</span> <span class="token keyword">SESSION</span> <span class="token keyword">VARIABLES</span> <span class="token operator">LIKE</span> <span class="token string">'character\_set\_%'</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> Variable_name <span class="token punctuation">|</span> Value <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> character_set_client <span class="token punctuation">|</span> latin1 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> character_set_connection <span class="token punctuation">|</span> latin1 <span class="token punctuation">|</span></span>
<span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token output"><span class="token punctuation">|</span> character_set_results <span class="token punctuation">|</span> latin1 <span class="token punctuation">|</span></span>
<span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token prompt">mysql></span> <span class="token keyword">SHOW</span> <span class="token keyword">SESSION</span> <span class="token keyword">VARIABLES</span> <span class="token operator">LIKE</span> <span class="token string">'collation_connection'</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> Variable_name <span class="token punctuation">|</span> Value <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> collation_connection <span class="token punctuation">|</span> latin1_swedish_ci <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span></code></pre>
</div>
<p>
You can see that the connection system variables have been set
to reflect a character set and collation of
<code class="literal">
latin1
</code>
and
<code class="literal">
latin1_swedish_ci
</code>
. This occurs because the
server cannot satisfy the client character set request and falls
back to its defaults.
</p>
<p>
In this case, the client cannot use the character set that it
wants because the server does not support it. The client must
either be willing to use a different character set, or connect
to a different server that supports the desired character set.
</p>
<p>
The same problem occurs when the client tells the server to use
a character set that the server recognizes, but the default
collation for that character set on the client side is not known
on the server side.
</p>
<h4>
<a name="charset-connection-error-handling-runtime">
</a>
Runtime Error Handling
</h4>
<p>
Within an established connection, the client can request a
change of connection character set and collation with
<a class="link" href="set-names.html" title="15.7.6.3 SET NAMES Statement">
<code class="literal">
SET NAMES
</code>
</a>
or
<a class="link" href="set-character-set.html" title="15.7.6.2 SET CHARACTER SET Statement">
<code class="literal">
SET CHARACTER SET
</code>
</a>
.
</p>
<p>
Some character sets cannot be used as the client character set;
see
<a class="xref" href="charset-connection.html#charset-connection-impermissible-client-charset" title="Impermissible Client Character Sets">
Impermissible Client Character Sets
</a>
.
If you specify a character set that is valid but not permitted
as a client character set, the server returns an error:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa47963678"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SET</span> <span class="token keyword">NAMES</span> <span class="token string">'ucs2'</span><span class="token punctuation">;</span>
<span class="token output">ERROR 1231 (42000)<span class="token punctuation">:</span> Variable 'character_set_client' can't be set to
the value of 'ucs2'</span></code></pre>
</div>
<p>
If the server does not recognize the character set (or the
collation), it produces an error:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa68250687"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SET</span> <span class="token keyword">NAMES</span> <span class="token string">'bogus'</span><span class="token punctuation">;</span>
<span class="token output">ERROR 1115 (42000)<span class="token punctuation">:</span> Unknown character set<span class="token punctuation">:</span> 'bogus'
</span>
<span class="token prompt">mysql></span> <span class="token keyword">SET</span> <span class="token keyword">NAMES</span> <span class="token string">'utf8mb4'</span> <span class="token keyword">COLLATE</span> <span class="token string">'bogus'</span><span class="token punctuation">;</span>
<span class="token output">ERROR 1273 (HY000)<span class="token punctuation">:</span> Unknown collation<span class="token punctuation">:</span> 'bogus'</span></code></pre>
</div>
<div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Tip
</div>
<p>
A client that wants to verify whether its requested character
set was honored by the server can execute the following
statement after connecting and checking that the result is the
expected character set:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa96308007"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">SELECT</span> <span class="token variable">@@character_set_client</span><span class="token punctuation">;</span></code></pre>
</div>
</div>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/loop.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="loop">
</a>
15.6.5.5 LOOP Statement
</h4>
</div>
</div>
</div>
<a class="indexterm" name="idm46045176242880">
</a>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa39865881"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token punctuation">[</span><em class="replaceable">begin_label</em>:<span class="token punctuation">]</span> <span class="token keyword">LOOP</span>
<em class="replaceable">statement_list</em>
<span class="token keyword">END</span> <span class="token keyword">LOOP</span> <span class="token punctuation">[</span><em class="replaceable">end_label</em><span class="token punctuation">]</span></code></pre>
</div>
<p>
<a class="link" href="loop.html" title="15.6.5.5 LOOP Statement">
<code class="literal">
LOOP
</code>
</a>
implements a simple loop
construct, enabling repeated execution of the statement list,
which consists of one or more statements, each terminated by a
semicolon (
<code class="literal">
;
</code>
) statement delimiter. The
statements within the loop are repeated until the loop is
terminated. Usually, this is accomplished with a
<a class="link" href="leave.html" title="15.6.5.4 LEAVE Statement">
<code class="literal">
LEAVE
</code>
</a>
statement. Within a stored
function,
<a class="link" href="return.html" title="15.6.5.7 RETURN Statement">
<code class="literal">
RETURN
</code>
</a>
can also be
used, which exits the function entirely.
</p>
<p>
Neglecting to include a loop-termination statement results in an
infinite loop.
</p>
<p>
A
<a class="link" href="loop.html" title="15.6.5.5 LOOP Statement">
<code class="literal">
LOOP
</code>
</a>
statement can be labeled.
For the rules regarding label use, see
<a class="xref" href="statement-labels.html" title="15.6.2 Statement Labels">
Section 15.6.2, “Statement Labels”
</a>
.
</p>
<p>
Example:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa44847399"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">PROCEDURE</span> doiterate<span class="token punctuation">(</span>p1 <span class="token datatype">INT</span><span class="token punctuation">)</span>
<span class="token keyword">BEGIN</span>
label1: <span class="token keyword">LOOP</span>
<span class="token keyword">SET</span> p1 <span class="token operator">=</span> p1 <span class="token operator">+</span> <span class="token number">1</span><span class="token punctuation">;</span>
<span class="token keyword">IF</span> p1 <span class="token operator"><</span> <span class="token number">10</span> <span class="token keyword">THEN</span>
<span class="token keyword">ITERATE</span> label1<span class="token punctuation">;</span>
<span class="token keyword">END</span> <span class="token keyword">IF</span><span class="token punctuation">;</span>
<span class="token keyword">LEAVE</span> label1<span class="token punctuation">;</span>
<span class="token keyword">END</span> <span class="token keyword">LOOP</span> label1<span class="token punctuation">;</span>
<span class="token keyword">SET</span> <span class="token variable">@x</span> <span class="token operator">=</span> p1<span class="token punctuation">;</span>
<span class="token keyword">END</span><span class="token punctuation">;</span></code></pre>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/binlog-replication-configuration-overview.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="binlog-replication-configuration-overview">
</a>
19.1.1 Binary Log File Position Based Replication Configuration Overview
</h3>
</div>
</div>
</div>
<p>
This section describes replication between MySQL servers based on
the binary log file position method, where the MySQL instance
operating as the source (where the database changes take place)
writes updates and changes as
<span class="quote">
“
<span class="quote">
events
</span>
”
</span>
to the binary
log. The information in the binary log is stored in different
logging formats according to the database changes being recorded.
Replicas are configured to read the binary log from the source and
to execute the events in the binary log on the replica's local
database.
</p>
<p>
Each replica receives a copy of the entire contents of the binary
log. It is the responsibility of the replica to decide which
statements in the binary log should be executed. Unless you
specify otherwise, all events in the source's binary log are
executed on the replica. If required, you can configure the
replica to process only events that apply to particular databases
or tables.
</p>
<div class="important" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Important
</div>
<p>
You cannot configure the source to log only certain events.
</p>
</div>
<p>
Each replica keeps a record of the binary log coordinates: the
file name and position within the file that it has read and
processed from the source. This means that multiple replicas can
be connected to the source and executing different parts of the
same binary log. Because the replicas control this process,
individual replicas can be connected and disconnected from the
server without affecting the source's operation. Also, because
each replica records the current position within the binary log,
it is possible for replicas to be disconnected, reconnect and then
resume processing.
</p>
<p>
The source and each replica must be configured with a unique ID
(using the
<a class="link" href="replication-options.html#sysvar_server_id">
<code class="literal">
server_id
</code>
</a>
system
variable). In addition, each replica must be configured with
information about the source's host name, log file name, and
position within that file. These details can be controlled from
within a MySQL session using a
<a class="link" href="change-replication-source-to.html" title="15.4.2.2 CHANGE REPLICATION SOURCE TO Statement">
<code class="literal">
CHANGE
REPLICATION SOURCE TO
</code>
</a>
statement on the replica. The
details are stored within the replica's connection metadata
repository (see
<a class="xref" href="replica-logs.html" title="19.2.4 Relay Log and Replication Metadata Repositories">
Section 19.2.4, “Relay Log and Replication Metadata Repositories”
</a>
).
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/verifying-index-usage.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="verifying-index-usage">
</a>
10.3.7 Verifying Index Usage
</h3>
</div>
</div>
</div>
<p>
Always check whether all your queries really use the indexes
that you have created in the tables. Use the
<a class="link" href="explain.html" title="15.8.2 EXPLAIN Statement">
<code class="literal">
EXPLAIN
</code>
</a>
statement, as described
in
<a class="xref" href="using-explain.html" title="10.8.1 Optimizing Queries with EXPLAIN">
Section 10.8.1, “Optimizing Queries with EXPLAIN”
</a>
.
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/version-tokens-elements.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="version-tokens-elements">
</a>
7.6.6.1 Version Tokens Elements
</h4>
</div>
</div>
</div>
<a class="indexterm" name="idm46045256123648">
</a>
<p>
Version Tokens is based on a plugin library that implements
these elements:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
A server-side plugin named
<code class="literal">
version_tokens
</code>
holds the list of version tokens associated with the server
and subscribes to notifications for statement execution
events. The
<code class="literal">
version_tokens
</code>
plugin uses
the
<a class="ulink" href="/doc/extending-mysql/8.4/en/plugin-types.html#audit-plugin-type" target="_top">
audit plugin
API
</a>
to monitor incoming statements from clients and
matches each client's session-specific version token list
against the server version token list. If there is a match,
the plugin lets the statement through and the server
continues to process it. Otherwise, the plugin returns an
error to the client and the statement fails.
</p>
</li>
<li class="listitem">
<p>
A set of loadable functions provides an SQL-level API for
manipulating and inspecting the list of server version
tokens maintained by the plugin. The
<a class="link" href="privileges-provided.html#priv_version-token-admin">
<code class="literal">
VERSION_TOKEN_ADMIN
</code>
</a>
privilege
(or the deprecated
<a class="link" href="privileges-provided.html#priv_super">
<code class="literal">
SUPER
</code>
</a>
privilege) is required to call any of the Version Token
functions.
</p>
</li>
<li class="listitem">
<p>
When the
<code class="literal">
version_tokens
</code>
plugin loads, it
defines the
<a class="link" href="privileges-provided.html#priv_version-token-admin">
<code class="literal">
VERSION_TOKEN_ADMIN
</code>
</a>
dynamic
privilege. This privilege can be granted to users of the
functions.
</p>
</li>
<li class="listitem">
<p>
A system variable enables clients to specify the list of
version tokens that register the required server state. If
the server has a different state when a client sends a
statement, the client receives an error.
</p>
</li>
</ul>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/performance-schema-setup-metrics-table.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="performance-schema-setup-metrics-table">
</a>
29.12.21.2 The setup_metrics Table
</h4>
</div>
</div>
</div>
<a class="indexterm" name="idm46045067827248">
</a>
<a class="indexterm" name="idm46045067825760">
</a>
<p>
The
<a class="link" href="performance-schema-setup-metrics-table.html" title="29.12.21.2 The setup_metrics Table">
<code class="literal">
setup_metrics
</code>
</a>
table lists the
available metrics:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa92491329"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">select</span> <span class="token operator">*</span> <span class="token keyword">from</span> performance_schema<span class="token punctuation">.</span>setup_metrics\G
<span class="token output"><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span> 34. row <span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span>
NAME<span class="token punctuation">:</span> undo_tablespaces_active
METER<span class="token punctuation">:</span> mysql.inno
METRIC_TYPE<span class="token punctuation">:</span> ASYNC GAUGE COUNTER
NUM_TYPE<span class="token punctuation">:</span> INTEGER
UNIT<span class="token punctuation">:</span>
DESCRIPTION<span class="token punctuation">:</span> Number of active undo tablespaces, including implicit and explicit tablespaces (innodb_undo_tablespaces_active)
...
<span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span> 48. row <span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span>
NAME<span class="token punctuation">:</span> wait_free
METER<span class="token punctuation">:</span> mysql.inno.buffer_pool
METRIC_TYPE<span class="token punctuation">:</span> ASYNC COUNTER
NUM_TYPE<span class="token punctuation">:</span> INTEGER
UNIT<span class="token punctuation">:</span>
DESCRIPTION<span class="token punctuation">:</span> Number of times waited for free buffer (innodb_buffer_pool_wait_free)
...
<span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span> 55. row <span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span>
NAME<span class="token punctuation">:</span> reads
METER<span class="token punctuation">:</span> mysql.inno.data
METRIC_TYPE<span class="token punctuation">:</span> ASYNC COUNTER
NUM_TYPE<span class="token punctuation">:</span> INTEGER
UNIT<span class="token punctuation">:</span>
DESCRIPTION<span class="token punctuation">:</span> Number of reads initiated (innodb_data_reads)
...
<span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span> 101. row <span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span>
NAME<span class="token punctuation">:</span> ssl_finished_accepts
METER<span class="token punctuation">:</span> mysql.x
METRIC_TYPE<span class="token punctuation">:</span> ASYNC COUNTER
NUM_TYPE<span class="token punctuation">:</span> INTEGER
UNIT<span class="token punctuation">:</span>
DESCRIPTION<span class="token punctuation">:</span> The number of successful SSL connections to the server (Mysqlx_ssl_finished_accepts)
...
<span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span> 115. row <span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span>
NAME<span class="token punctuation">:</span> list_clients
METER<span class="token punctuation">:</span> mysql.x.stmt
METRIC_TYPE<span class="token punctuation">:</span> ASYNC COUNTER
NUM_TYPE<span class="token punctuation">:</span> INTEGER
UNIT<span class="token punctuation">:</span>
DESCRIPTION<span class="token punctuation">:</span> The number of list client statements received (Mysqlx_stmt_list_clients)
...
<span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span> 162. row <span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span>
NAME<span class="token punctuation">:</span> slow_queries
METER<span class="token punctuation">:</span> mysql.stats
METRIC_TYPE<span class="token punctuation">:</span> ASYNC COUNTER
NUM_TYPE<span class="token punctuation">:</span> INTEGER
UNIT<span class="token punctuation">:</span>
DESCRIPTION<span class="token punctuation">:</span> The number of queries that have taken more than long_query_time seconds (Slow_queries)
...
<span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span> 346. row <span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span>
NAME<span class="token punctuation">:</span> stmt_reprepare
METER<span class="token punctuation">:</span> mysql.stats.com
METRIC_TYPE<span class="token punctuation">:</span> ASYNC COUNTER
NUM_TYPE<span class="token punctuation">:</span> INTEGER
UNIT<span class="token punctuation">:</span>
DESCRIPTION<span class="token punctuation">:</span> Number of times corresponding command statement has been executed.
...
<span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span> 353. row <span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span>
NAME<span class="token punctuation">:</span> errors_tcpwrap
METER<span class="token punctuation">:</span> mysql.stats.connection
METRIC_TYPE<span class="token punctuation">:</span> ASYNC COUNTER
NUM_TYPE<span class="token punctuation">:</span> INTEGER
UNIT<span class="token punctuation">:</span>
DESCRIPTION<span class="token punctuation">:</span> The number of connections refused by the libwrap library (Connection_errors_tcpwrap)
...
<span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span> 370. row <span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span>
NAME<span class="token punctuation">:</span> update
METER<span class="token punctuation">:</span> mysql.stats.handler
METRIC_TYPE<span class="token punctuation">:</span> ASYNC COUNTER
NUM_TYPE<span class="token punctuation">:</span> INTEGER
UNIT<span class="token punctuation">:</span>
DESCRIPTION<span class="token punctuation">:</span> The number of requests to update a row in a table (Handler_update)
...
<span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span> 384. row <span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span>
NAME<span class="token punctuation">:</span> callback_cache_hits
METER<span class="token punctuation">:</span> mysql.stats.ssl
METRIC_TYPE<span class="token punctuation">:</span> ASYNC COUNTER
NUM_TYPE<span class="token punctuation">:</span> INTEGER
UNIT<span class="token punctuation">:</span>
DESCRIPTION<span class="token punctuation">:</span> The number of accepted SSL connections (Ssl_callback_cache_hits)
...
<span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span> 391. row <span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span>
NAME<span class="token punctuation">:</span> key_writes
METER<span class="token punctuation">:</span> mysql.myisam
METRIC_TYPE<span class="token punctuation">:</span> ASYNC COUNTER
NUM_TYPE<span class="token punctuation">:</span> INTEGER
UNIT<span class="token punctuation">:</span>
DESCRIPTION<span class="token punctuation">:</span> The number of physical writes of a key block from the MyISAM key cache to disk (Key_writes)
...
<span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span> 424. row <span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span>
NAME<span class="token punctuation">:</span> users_lost
METER<span class="token punctuation">:</span> mysql.perf_schema
METRIC_TYPE<span class="token punctuation">:</span> ASYNC COUNTER
NUM_TYPE<span class="token punctuation">:</span> INTEGER
UNIT<span class="token punctuation">:</span>
DESCRIPTION<span class="token punctuation">:</span> The number of times a row could not be added to the users table because it was full (Performance_schema_users_lost)</span></code></pre>
</div>
<p>
The
<a class="link" href="performance-schema-setup-metrics-table.html" title="29.12.21.2 The setup_metrics Table">
<code class="literal">
setup_metrics
</code>
</a>
table has the
following columns:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<code class="literal">
NAME
</code>
: Name of the metric.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
METER
</code>
: Name of the meter group of the
metric.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
METRIC_TYPE
</code>
: The OpenTelemetry metric
type.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
NUM_TYPE
</code>
: The numeric type.
<code class="literal">
INTEGER
</code>
or
<code class="literal">
DOUBLE
</code>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
DESCRIPTION
</code>
: A string describing the
metric's purpose.
</p>
</li>
</ul>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/innodb-multi-versioning.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h2 class="title">
<a name="innodb-multi-versioning">
</a>
17.3 InnoDB Multi-Versioning
</h2>
</div>
</div>
</div>
<a class="indexterm" name="idm46045167232032">
</a>
<a class="indexterm" name="idm46045167230544">
</a>
<p>
<code class="literal">
InnoDB
</code>
is a multi-version storage engine. It
keeps information about old versions of changed rows to support
transactional features such as concurrency and rollback. This
information is stored in undo tablespaces in a data structure called
a rollback segment. See
<a class="xref" href="innodb-undo-tablespaces.html" title="17.6.3.4 Undo Tablespaces">
Section 17.6.3.4, “Undo Tablespaces”
</a>
.
<code class="literal">
InnoDB
</code>
uses the information in the rollback
segment to perform the undo operations needed in a transaction
rollback. It also uses the information to build earlier versions of
a row for a consistent read. See
<a class="xref" href="innodb-consistent-read.html" title="17.7.2.3 Consistent Nonlocking Reads">
Section 17.7.2.3, “Consistent Nonlocking Reads”
</a>
.
</p>
<p>
Internally,
<code class="literal">
InnoDB
</code>
adds three fields to each row
stored in the database:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
A 6-byte
<code class="literal">
DB_TRX_ID
</code>
field indicates the
transaction identifier for the last transaction that inserted or
updated the row. Also, a deletion is treated internally as an
update where a special bit in the row is set to mark it as
deleted.
</p>
</li>
<li class="listitem">
<p>
A 7-byte
<code class="literal">
DB_ROLL_PTR
</code>
field called the roll
pointer. The roll pointer points to an undo log record written
to the rollback segment. If the row was updated, the undo log
record contains the information necessary to rebuild the content
of the row before it was updated.
</p>
</li>
<li class="listitem">
<p>
A 6-byte
<code class="literal">
DB_ROW_ID
</code>
field contains a row ID
that increases monotonically as new rows are inserted. If
<code class="literal">
InnoDB
</code>
generates a clustered index
automatically, the index contains row ID values. Otherwise, the
<code class="literal">
DB_ROW_ID
</code>
column does not appear in any
index.
</p>
</li>
</ul>
</div>
<p>
Undo logs in the rollback segment are divided into insert and update
undo logs. Insert undo logs are needed only in transaction rollback
and can be discarded as soon as the transaction commits. Update undo
logs are used also in consistent reads, but they can be discarded
only after there is no transaction present for which
<code class="literal">
InnoDB
</code>
has assigned a snapshot that in a
consistent read could require the information in the update undo log
to build an earlier version of a database row. For additional
information about undo logs, see
<a class="xref" href="innodb-undo-logs.html" title="17.6.6 Undo Logs">
Section 17.6.6, “Undo Logs”
</a>
.
</p>
<p>
It is recommend that you commit transactions regularly, including
transactions that issue only consistent reads. Otherwise,
<code class="literal">
InnoDB
</code>
cannot discard data from the update undo
logs, and the rollback segment may grow too big, filling up the undo
tablespace in which it resides. For information about managing undo
tablespaces, see
<a class="xref" href="innodb-undo-tablespaces.html" title="17.6.3.4 Undo Tablespaces">
Section 17.6.3.4, “Undo Tablespaces”
</a>
.
</p>
<p>
The physical size of an undo log record in the rollback segment is
typically smaller than the corresponding inserted or updated row.
You can use this information to calculate the space needed for your
rollback segment.
</p>
<p>
In the
<code class="literal">
InnoDB
</code>
multi-versioning scheme, a row is
not physically removed from the database immediately when you delete
it with an SQL statement.
<code class="literal">
InnoDB
</code>
only physically
removes the corresponding row and its index records when it discards
the update undo log record written for the deletion. This removal
operation is called a purge, and it is quite fast, usually taking
the same order of time as the SQL statement that did the deletion.
</p>
<p>
If you insert and delete rows in smallish batches at about the same
rate in the table, the purge thread can start to lag behind and the
table can grow bigger and bigger because of all the
<span class="quote">
“
<span class="quote">
dead
</span>
”
</span>
rows, making everything disk-bound and very
slow. In such cases, throttle new row operations, and allocate more
resources to the purge thread by tuning the
<a class="link" href="innodb-parameters.html#sysvar_innodb_max_purge_lag">
<code class="literal">
innodb_max_purge_lag
</code>
</a>
system
variable. For more information, see
<a class="xref" href="innodb-purge-configuration.html" title="17.8.9 Purge Configuration">
Section 17.8.9, “Purge Configuration”
</a>
.
</p>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h3 class="title">
<a name="innodb-multi-versioning-secondary-indexes">
</a>
Multi-Versioning and Secondary Indexes
</h3>
</div>
</div>
</div>
<p>
<code class="literal">
InnoDB
</code>
multiversion concurrency control (MVCC)
treats secondary indexes differently than clustered indexes.
Records in a clustered index are updated in-place, and their
hidden system columns point undo log entries from which earlier
versions of records can be reconstructed. Unlike clustered index
records, secondary index records do not contain hidden system
columns nor are they updated in-place.
</p>
<p>
When a secondary index column is updated, old secondary index
records are delete-marked, new records are inserted, and
delete-marked records are eventually purged. When a secondary
index record is delete-marked or the secondary index page is
updated by a newer transaction,
<code class="literal">
InnoDB
</code>
looks up
the database record in the clustered index. In the clustered
index, the record's
<code class="literal">
DB_TRX_ID
</code>
is checked, and
the correct version of the record is retrieved from the undo log
if the record was modified after the reading transaction was
initiated.
</p>
<p>
If a secondary index record is marked for deletion or the
secondary index page is updated by a newer transaction, the
<a class="link" href="glossary.html#glos_covering_index" title="covering index">
covering index
</a>
technique is not used. Instead of returning values from the index
structure,
<code class="literal">
InnoDB
</code>
looks up the record in the
clustered index.
</p>
<p>
However, if the
<a class="link" href="index-condition-pushdown-optimization.html" title="10.2.1.6 Index Condition Pushdown Optimization">
index
condition pushdown (ICP)
</a>
optimization is enabled, and parts
of the
<code class="literal">
WHERE
</code>
condition can be evaluated using
only fields from the index, the MySQL server still pushes this
part of the
<code class="literal">
WHERE
</code>
condition down to the storage
engine where it is evaluated using the index. If no matching
records are found, the clustered index lookup is avoided. If
matching records are found, even among delete-marked records,
<code class="literal">
InnoDB
</code>
looks up the record in the clustered
index.
</p>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/sys-ps-is-instrument-default-timed.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="sys-ps-is-instrument-default-timed">
</a>
30.4.5.12 The ps_is_instrument_default_timed() Function
</h4>
</div>
</div>
</div>
<a class="indexterm" name="idm46045060840288">
</a>
<a class="indexterm" name="idm46045060838768">
</a>
<p>
Returns
<code class="literal">
YES
</code>
or
<code class="literal">
NO
</code>
to
indicate whether a given Performance Schema instrument is
timed by default.
</p>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h5 class="title">
<a name="sys-ps-is-instrument-default-timed-parameters">
</a>
Parameters
</h5>
</div>
</div>
</div>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<code class="literal">
in_instrument VARCHAR(128)
</code>
: The name
of the instrument to check.
</p>
</li>
</ul>
</div>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h5 class="title">
<a name="sys-ps-is-instrument-default-timed-return-value">
</a>
Return Value
</h5>
</div>
</div>
</div>
<p>
An
<code class="literal">
ENUM('YES','NO')
</code>
value.
</p>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h5 class="title">
<a name="sys-ps-is-instrument-default-timed-example">
</a>
Example
</h5>
</div>
</div>
</div>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa14479544"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> sys<span class="token punctuation">.</span>ps_is_instrument_default_timed<span class="token punctuation">(</span><span class="token string">'memory/innodb/row_log_buf'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> sys.ps_is_instrument_default_timed('memory/innodb/row_log_buf') <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> NO <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> sys<span class="token punctuation">.</span>ps_is_instrument_default_timed<span class="token punctuation">(</span><span class="token string">'statement/sql/alter_user'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> sys.ps_is_instrument_default_timed('statement/sql/alter_user') <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> YES <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span></code></pre>
</div>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/replication-features.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="replication-features">
</a>
19.5.1 Replication Features and Issues
</h3>
</div>
</div>
</div>
<div class="toc">
<dl class="toc">
<dt>
<span class="section">
<a href="replication-features-auto-increment.html">
19.5.1.1 Replication and AUTO_INCREMENT
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-blackhole.html">
19.5.1.2 Replication and BLACKHOLE Tables
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-charset.html">
19.5.1.3 Replication and Character Sets
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-checksum-table.html">
19.5.1.4 Replication and CHECKSUM TABLE
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-create-alter-drop-server.html">
19.5.1.5 Replication of CREATE SERVER, ALTER SERVER, and DROP SERVER
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-create-if-not-exists.html">
19.5.1.6 Replication of CREATE ... IF NOT EXISTS Statements
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-create-select.html">
19.5.1.7 Replication of CREATE TABLE ... SELECT Statements
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-current-user.html">
19.5.1.8 Replication of CURRENT_USER()
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-differing-tables.html">
19.5.1.9 Replication with Differing Table Definitions on Source and Replica
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-directory.html">
19.5.1.10 Replication and DIRECTORY Table Options
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-drop-if-exists.html">
19.5.1.11 Replication of DROP ... IF EXISTS Statements
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-floatvalues.html">
19.5.1.12 Replication and Floating-Point Values
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-flush.html">
19.5.1.13 Replication and FLUSH
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-functions.html">
19.5.1.14 Replication and System Functions
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-fractional-seconds.html">
19.5.1.15 Replication and Fractional Seconds Support
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-invoked.html">
19.5.1.16 Replication of Invoked Features
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-json.html">
19.5.1.17 Replication of JSON Documents
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-limit.html">
19.5.1.18 Replication and LIMIT
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-load-data.html">
19.5.1.19 Replication and LOAD DATA
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-max-allowed-packet.html">
19.5.1.20 Replication and max_allowed_packet
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-memory.html">
19.5.1.21 Replication and MEMORY Tables
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-mysqldb.html">
19.5.1.22 Replication of the mysql System Schema
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-optimizer.html">
19.5.1.23 Replication and the Query Optimizer
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-partitioning.html">
19.5.1.24 Replication and Partitioning
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-repair-table.html">
19.5.1.25 Replication and REPAIR TABLE
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-reserved-words.html">
19.5.1.26 Replication and Reserved Words
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-row-searches.html">
19.5.1.27 Replication and Row Searches
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-shutdowns.html">
19.5.1.28 Replication and Source or Replica Shutdowns
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-errors.html">
19.5.1.29 Replica Errors During Replication
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-sql-mode.html">
19.5.1.30 Replication and Server SQL Mode
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-temptables.html">
19.5.1.31 Replication and Temporary Tables
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-timeout.html">
19.5.1.32 Replication Retries and Timeouts
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-timezone.html">
19.5.1.33 Replication and Time Zones
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-transaction-inconsistencies.html">
19.5.1.34 Replication and Transaction Inconsistencies
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-transactions.html">
19.5.1.35 Replication and Transactions
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-triggers.html">
19.5.1.36 Replication and Triggers
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-truncate.html">
19.5.1.37 Replication and TRUNCATE TABLE
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-user-names.html">
19.5.1.38 Replication and User Name Length
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-variables.html">
19.5.1.39 Replication and Variables
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="replication-features-views.html">
19.5.1.40 Replication and Views
</a>
</span>
</dt>
</dl>
</div>
<a class="indexterm" name="idm46045136027184">
</a>
<a class="indexterm" name="idm46045136025728">
</a>
<a class="indexterm" name="idm46045136024656">
</a>
<a class="indexterm" name="idm46045136023168">
</a>
<a class="indexterm" name="idm46045136022096">
</a>
<a class="indexterm" name="idm46045136021024">
</a>
<p>
The following sections provide information about what is supported
and what is not in MySQL replication, and about specific issues
and situations that may occur when replicating certain statements.
</p>
<p>
Statement-based replication depends on compatibility at the SQL
level between the source and replica. In other words, successful
statement-based replication requires that any SQL features used be
supported by both the source and the replica servers. If you use a
feature on the source server that is available only in the current
version of MySQL, you cannot replicate to a replica that uses an
earlier version of MySQL. Such incompatibilities can also occur
within a release series as well as between versions.
</p>
<p>
If you are planning to use statement-based replication between
MySQL 8.4 and a previous MySQL release series, it is
a good idea to consult the edition of the
<em class="citetitle">
MySQL
Reference Manual
</em>
corresponding to the earlier release
series for information regarding the replication characteristics
of that series.
</p>
<p>
With MySQL's statement-based replication, there may be issues with
replicating stored routines or triggers. You can avoid these
issues by using MySQL's row-based replication instead. For a
detailed list of issues, see
<a class="xref" href="stored-programs-logging.html" title="27.7 Stored Program Binary Logging">
Section 27.7, “Stored Program Binary Logging”
</a>
. For more information
about row-based logging and row-based replication, see
<a class="xref" href="binary-log-formats.html" title="7.4.4.1 Binary Logging Formats">
Section 7.4.4.1, “Binary Logging Formats”
</a>
, and
<a class="xref" href="replication-formats.html" title="19.2.1 Replication Formats">
Section 19.2.1, “Replication Formats”
</a>
.
</p>
<p>
For additional information specific to replication and
<code class="literal">
InnoDB
</code>
, see
<a class="xref" href="innodb-and-mysql-replication.html" title="17.19 InnoDB and MySQL Replication">
Section 17.19, “InnoDB and MySQL Replication”
</a>
. For information
relating to replication with NDB Cluster, see
<a class="xref" href="mysql-cluster-replication.html" title="25.7 NDB Cluster Replication">
Section 25.7, “NDB Cluster Replication”
</a>
.
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/mysql-cluster-backup-using-management-client.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="mysql-cluster-backup-using-management-client">
</a>
25.6.8.2 Using The NDB Cluster Management Client to Create a Backup
</h4>
</div>
</div>
</div>
<a class="indexterm" name="idm46045092122352">
</a>
<a class="indexterm" name="idm46045092120864">
</a>
<p>
Before starting a backup, make sure that the cluster is properly
configured for performing one. (See
<a class="xref" href="mysql-cluster-backup-configuration.html" title="25.6.8.3 Configuration for NDB Cluster Backups">
Section 25.6.8.3, “Configuration for NDB Cluster Backups”
</a>
.)
</p>
<a class="indexterm" name="idm46045092118144">
</a>
<p>
The
<code class="literal">
START BACKUP
</code>
command is used to create a
backup, and has the syntax shown here:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-simple"><div class="docs-select-all right" id="sa54719513"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-simple">START BACKUP <span class="token punctuation">[</span><em class="replaceable">backup_id</em><span class="token punctuation">]</span>
<span class="token punctuation">[</span><em class="replaceable">encryption_option</em><span class="token punctuation">]</span>
<span class="token punctuation">[</span><em class="replaceable">wait_option</em><span class="token punctuation">]</span>
<span class="token punctuation">[</span><em class="replaceable">snapshot_option</em><span class="token punctuation">]</span>
<em class="replaceable">encryption_option</em><span class="token operator">:</span>
ENCRYPT <span class="token punctuation">[</span>PASSWORD<span class="token operator">=</span><em class="replaceable">password</em><span class="token punctuation">]</span>
<em class="replaceable">password</em><span class="token operator">:</span>
<span class="token punctuation">{</span>'<em class="replaceable">password_string</em>' <span class="token operator">|</span> "<em class="replaceable">password_string</em>"<span class="token punctuation">}</span>
<em class="replaceable">wait_option</em><span class="token operator">:</span>
WAIT <span class="token punctuation">{</span>STARTED <span class="token operator">|</span> COMPLETED<span class="token punctuation">}</span> <span class="token operator">|</span> NOWAIT
<em class="replaceable">snapshot_option</em><span class="token operator">:</span>
SNAPSHOTSTART <span class="token operator">|</span> SNAPSHOTEND</code></pre>
</div>
<p>
Successive backups are automatically identified sequentially, so
the
<em class="replaceable">
<code>
backup_id
</code>
</em>
, an integer greater
than or equal to 1, is optional; if it is omitted, the next
available value is used. If an existing
<em class="replaceable">
<code>
backup_id
</code>
</em>
value is used, the backup
fails with the error
<span class="errortext">
Backup failed: file already
exists
</span>
. If used, the
<em class="replaceable">
<code>
backup_id
</code>
</em>
must follow immediately
after the
<code class="literal">
START BACKUP
</code>
keywords, before any
other options are used.
</p>
<p>
<code class="literal">
START BACKUP
</code>
supports the creation of
encrypted backups using
<code class="literal">
ENCRYPT
PASSWORD=
<em class="replaceable">
<code>
password
</code>
</em>
</code>
. The
<em class="replaceable">
<code>
password
</code>
</em>
must meet all of the
following requirements:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
Uses any of the printable ASCII characters except
<code class="literal">
!
</code>
,
<code class="literal">
'
</code>
,
<code class="literal">
"
</code>
,
<code class="literal">
$
</code>
,
<code class="literal">
%
</code>
,
<code class="literal">
\
</code>
, and
<code class="literal">
^
</code>
</p>
</li>
<li class="listitem">
<p>
Is no more than 256 characters in length
</p>
</li>
<li class="listitem">
<p>
Is enclosed by single or double quotation marks
</p>
</li>
</ul>
</div>
<p>
When
<code class="literal">
ENCRYPT
PASSWORD='
<em class="replaceable">
<code>
password
</code>
</em>
'
</code>
is
used, the backup data record and log files written by each data
node are encrypted with a key derived from the user-provided
<em class="replaceable">
<code>
password
</code>
</em>
and a randomly-generated
salt using a key derivation function (KDF) that employs the
PBKDF2-SHA256 algorithm to generate a symmetric encryption key
for that file. This function has the form shown here:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-simple"><div class="docs-select-all right" id="sa53968037"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-simple">key <span class="token operator">=</span> KDF<span class="token punctuation">(</span><em class="replaceable">random_salt</em><span class="token punctuation">,</span> <em class="replaceable">password</em><span class="token punctuation">)</span></code></pre>
</div>
<p>
The key so generated is then used to encrypt the backup data
using AES 256 CBC inline, and symmetric encryption is employed
for encrypting the backup fileset (with the generated key).
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
NDB Cluster
<span class="emphasis">
<em>
never
</em>
</span>
saves the
user-furnished password or generated encryption key.
</p>
</div>
<p>
The
<code class="literal">
PASSWORD
</code>
option can be omitted from
<em class="replaceable">
<code>
encryption_option
</code>
</em>
. In this case, the
management client prompts the user for a password.
</p>
<p>
It is possible using
<code class="literal">
PASSWORD
</code>
to set an empty
password (
<code class="literal">
''
</code>
or
<code class="literal">
""
</code>
), but
this is not recommended.
</p>
<p>
An encrypted backup can be decrypted using any of the following
commands:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<a class="link" href="mysql-cluster-programs-ndb-restore.html" title="25.5.23 ndb_restore — Restore an NDB Cluster Backup">
<span class="command">
<strong>
ndb_restore
</strong>
</span>
</a>
<a class="link" href="mysql-cluster-programs-ndb-restore.html#option_ndb_restore_decrypt">
<code class="option">
--decrypt
</code>
</a>
<a class="link" href="mysql-cluster-programs-ndb-restore.html#option_ndb_restore_backup-password">
<code class="option">
--backup-password=
<em class="replaceable">
<code>
password
</code>
</em>
</code>
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="link" href="mysql-cluster-programs-ndbxfrm.html" title="25.5.32 ndbxfrm — Compress, Decompress, Encrypt, and Decrypt Files Created by NDB Cluster">
<span class="command">
<strong>
ndbxfrm
</strong>
</span>
</a>
<a class="link" href="mysql-cluster-programs-ndbxfrm.html#option_ndbxfrm_decrypt-password">
<code class="option">
--decrypt-password=
<em class="replaceable">
<code>
password
</code>
</em>
</code>
</a>
<em class="replaceable">
<code>
input_file
</code>
</em>
<em class="replaceable">
<code>
output_file
</code>
</em>
</p>
</li>
<li class="listitem">
<p>
<a class="link" href="mysql-cluster-programs-ndb-print-backup-file.html" title="25.5.17 ndb_print_backup_file — Print NDB Backup File Contents">
<span class="command">
<strong>
ndb_print_backup_file
</strong>
</span>
</a>
<a class="link" href="mysql-cluster-programs-ndb-print-backup-file.html#option_ndb_print_backup_file_backup-password">
<code class="option">
-P
</code>
</a>
<em class="replaceable">
<code>
password
</code>
</em>
<em class="replaceable">
<code>
file_name
</code>
</em>
</p>
</li>
<li class="listitem">
<p>
<a class="link" href="mysql-cluster-programs-ndb-restore.html" title="25.5.23 ndb_restore — Restore an NDB Cluster Backup">
<span class="command">
<strong>
ndb_restore
</strong>
</span>
</a>
<a class="link" href="mysql-cluster-programs-ndb-restore.html#option_ndb_restore_decrypt">
<code class="option">
--decrypt
</code>
</a>
<a class="link" href="mysql-cluster-programs-ndb-restore.html#option_ndb_restore_backup-password-from-stdin">
<code class="option">
--backup-password-from-stdin
</code>
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="link" href="mysql-cluster-programs-ndbxfrm.html" title="25.5.32 ndbxfrm — Compress, Decompress, Encrypt, and Decrypt Files Created by NDB Cluster">
<span class="command">
<strong>
ndbxfrm
</strong>
</span>
</a>
<a class="link" href="mysql-cluster-programs-ndbxfrm.html#option_ndbxfrm_decrypt-password-from-stdin">
<code class="option">
--decrypt-password-from-stdin
</code>
</a>
<em class="replaceable">
<code>
input_file
</code>
</em>
<em class="replaceable">
<code>
output_file
</code>
</em>
</p>
</li>
<li class="listitem">
<p>
<a class="link" href="mysql-cluster-programs-ndb-print-backup-file.html" title="25.5.17 ndb_print_backup_file — Print NDB Backup File Contents">
<span class="command">
<strong>
ndb_print_backup_file
</strong>
</span>
</a>
<a class="link" href="mysql-cluster-programs-ndb-print-backup-file.html#option_ndb_print_backup_file_backup-password">
<code class="option">
--backup-password=
<em class="replaceable">
<code>
password
</code>
</em>
</code>
</a>
<em class="replaceable">
<code>
file_name
</code>
</em>
</p>
</li>
<li class="listitem">
<p>
<a class="link" href="mysql-cluster-programs-ndb-print-backup-file.html" title="25.5.17 ndb_print_backup_file — Print NDB Backup File Contents">
<span class="command">
<strong>
ndb_print_backup_file
</strong>
</span>
</a>
<a class="link" href="mysql-cluster-programs-ndb-print-backup-file.html#option_ndb_print_backup_file_backup-password-from-stdin">
<code class="option">
--backup-password-from-stdin
</code>
</a>
<em class="replaceable">
<code>
file_name
</code>
</em>
</p>
</li>
<li class="listitem">
<p>
<a class="link" href="mysql-cluster-programs-ndb-mgm.html" title="25.5.5 ndb_mgm — The NDB Cluster Management Client">
<span class="command">
<strong>
ndb_mgm
</strong>
</span>
</a>
<a class="link" href="mysql-cluster-programs-ndb-mgm.html#option_ndb_mgm_backup-password-from-stdin">
<code class="option">
--backup-password-from-stdin
</code>
</a>
<a class="link" href="mysql-cluster-programs-ndb-mgm.html#option_ndb_mgm_execute">
<code class="option">
--execute "START BACKUP ..."
</code>
</a>
</p>
</li>
</ul>
</div>
<p>
See the descriptions of these programs for more information,
such as additional options that may be required.
</p>
<p>
The
<em class="replaceable">
<code>
wait_option
</code>
</em>
can be used to
determine when control is returned to the management client
after a
<code class="literal">
START BACKUP
</code>
command is issued, as
shown in the following list:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<a class="indexterm" name="idm46045092050784">
</a>
<a class="indexterm" name="idm46045092049296">
</a>
If
<code class="literal">
NOWAIT
</code>
is specified, the management
client displays a prompt immediately, as seen here:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-ndbmgm"><div class="docs-select-all right" id="sa33229510"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-ndbmgm"><span class="token prompt">ndb_mgm></span> <span class="token keyword">START BACKUP</span> <span class="token keyword">NOWAIT</span>
<span class="token prompt">ndb_mgm></span></code></pre>
</div>
<p>
In this case, the management client can be used even while
it prints progress information from the backup process.
</p>
</li>
<li class="listitem">
<p>
<a class="indexterm" name="idm46045092044368">
</a>
<a class="indexterm" name="idm46045092042880">
</a>
With
<code class="literal">
WAIT STARTED
</code>
the management client
waits until the backup has started before returning control
to the user, as shown here:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-ndbmgm"><div class="docs-select-all right" id="sa28486569"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-ndbmgm"><span class="token prompt">ndb_mgm></span> <span class="token keyword">START BACKUP</span> <span class="token keyword">WAIT</span> <span class="token keyword">STARTED</span>
Waiting for started<span class="token punctuation">,</span> this may take several minutes
<span class="token selector">Node 2:</span> Backup 3 started from node 1
<span class="token prompt">ndb_mgm></span></code></pre>
</div>
</li>
<li class="listitem">
<p>
<a class="indexterm" name="idm46045092038272">
</a>
<a class="indexterm" name="idm46045092036784">
</a>
<strong class="userinput">
<code>
WAIT COMPLETED
</code>
</strong>
causes the management
client to wait until the backup process is complete before
returning control to the user.
</p>
</li>
</ul>
</div>
<p>
<code class="literal">
WAIT COMPLETED
</code>
is the default.
</p>
<p>
<a class="indexterm" name="idm46045092033104">
</a>
<a class="indexterm" name="idm46045092031616">
</a>
<a class="indexterm" name="idm46045092030528">
</a>
<a class="indexterm" name="idm46045092029040">
</a>
A
<em class="replaceable">
<code>
snapshot_option
</code>
</em>
can be used to
determine whether the backup matches the state of the cluster
when
<code class="literal">
START BACKUP
</code>
was issued, or when it was
completed.
<code class="literal">
SNAPSHOTSTART
</code>
causes the backup to
match the state of the cluster when the backup began;
<code class="literal">
SNAPSHOTEND
</code>
causes the backup to reflect the
state of the cluster when the backup was finished.
<code class="literal">
SNAPSHOTEND
</code>
is the default, and matches the
behavior found in previous NDB Cluster releases.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
If you use the
<code class="literal">
SNAPSHOTSTART
</code>
option with
<code class="literal">
START BACKUP
</code>
, and the
<a class="link" href="mysql-cluster-ndbd-definition.html#ndbparam-ndbd-compressedbackup">
<code class="literal">
CompressedBackup
</code>
</a>
parameter is enabled, only the data and control files are
compressed—the log file is not compressed.
</p>
</div>
<p>
If both a
<em class="replaceable">
<code>
wait_option
</code>
</em>
and a
<em class="replaceable">
<code>
snapshot_option
</code>
</em>
are used, they may be
specified in either order. For example, all of the following
commands are valid, assuming that there is no existing backup
having 4 as its ID:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-simple"><div class="docs-select-all right" id="sa97721612"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-simple">START BACKUP WAIT STARTED SNAPSHOTSTART
START BACKUP SNAPSHOTSTART WAIT STARTED
START BACKUP 4 WAIT COMPLETED SNAPSHOTSTART
START BACKUP SNAPSHOTEND WAIT COMPLETED
START BACKUP 4 NOWAIT SNAPSHOTSTART</code></pre>
</div>
<p>
The procedure for creating a backup consists of the following
steps:
</p>
<div class="orderedlist">
<ol class="orderedlist" type="1">
<li class="listitem">
<p>
Start the management client (
<a class="link" href="mysql-cluster-programs-ndb-mgm.html" title="25.5.5 ndb_mgm — The NDB Cluster Management Client">
<span class="command">
<strong>
ndb_mgm
</strong>
</span>
</a>
), if
it not running already.
</p>
</li>
<li class="listitem">
<p>
Execute the
<strong class="userinput">
<code>
START BACKUP
</code>
</strong>
command.
This produces several lines of output indicating the
progress of the backup, as shown here:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-ndbmgm"><div class="docs-select-all right" id="sa82770198"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-ndbmgm"><span class="token prompt">ndb_mgm></span> <span class="token keyword">START BACKUP</span>
Waiting for completed<span class="token punctuation">,</span> this may take several minutes
<span class="token selector">Node 2:</span> Backup 1 started from node 1
<span class="token selector">Node 2:</span> Backup 1 started from node 1 completed
StartGCP<span class="token operator">:</span> 177 StopGCP<span class="token operator">:</span> 180
#Records<span class="token operator">:</span> 7362 #LogRecords<span class="token operator">:</span> 0
Data<span class="token operator">:</span> 453648 bytes Log<span class="token operator">:</span> 0 bytes
<span class="token prompt">ndb_mgm></span></code></pre>
</div>
</li>
<li class="listitem">
<p>
<a class="indexterm" name="idm46045092010016">
</a>
<a class="indexterm" name="idm46045092008512">
</a>
When the backup has started the management client displays
this message:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-ndbmgm"><div class="docs-select-all right" id="sa54075452"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-ndbmgm">Backup <em class="replaceable">backup_id</em> started from node <em class="replaceable">node_id</em></code></pre>
</div>
<p>
<em class="replaceable">
<code>
backup_id
</code>
</em>
is the unique
identifier for this particular backup. This identifier is
saved in the cluster log, if it has not been configured
otherwise.
<em class="replaceable">
<code>
node_id
</code>
</em>
is the
identifier of the management server that is coordinating the
backup with the data nodes. At this point in the backup
process the cluster has received and processed the backup
request. It does not mean that the backup has finished. An
example of this statement is shown here:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-ndbmgm"><div class="docs-select-all right" id="sa45543041"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-ndbmgm"><span class="token selector">Node 2:</span> Backup 1 started from node 1</code></pre>
</div>
</li>
<li class="listitem">
<p>
The management client indicates with a message like this one
that the backup has started:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-ndbmgm"><div class="docs-select-all right" id="sa90060498"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-ndbmgm">Backup <em class="replaceable">backup_id</em> started from node <em class="replaceable">node_id</em> completed</code></pre>
</div>
<p>
As is the case for the notification that the backup has
started,
<em class="replaceable">
<code>
backup_id
</code>
</em>
is the unique
identifier for this particular backup, and
<em class="replaceable">
<code>
node_id
</code>
</em>
is the node ID of the
management server that is coordinating the backup with the
data nodes. This output is accompanied by additional
information including relevant global checkpoints, the
number of records backed up, and the size of the data, as
shown here:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-ndbmgm"><div class="docs-select-all right" id="sa74781969"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-ndbmgm"><span class="token selector">Node 2:</span> Backup 1 started from node 1 completed
StartGCP<span class="token operator">:</span> 177 StopGCP<span class="token operator">:</span> 180
#Records<span class="token operator">:</span> 7362 #LogRecords<span class="token operator">:</span> 0
Data<span class="token operator">:</span> 453648 bytes Log<span class="token operator">:</span> 0 bytes</code></pre>
</div>
</li>
</ol>
</div>
<p>
It is also possible to perform a backup from the system shell by
invoking
<a class="link" href="mysql-cluster-programs-ndb-mgm.html" title="25.5.5 ndb_mgm — The NDB Cluster Management Client">
<span class="command">
<strong>
ndb_mgm
</strong>
</span>
</a>
with the
<code class="option">
-e
</code>
or
<a class="link" href="mysql-cluster-programs-ndb-mgm.html#option_ndb_mgm_execute">
<code class="option">
--execute
</code>
</a>
option, as shown in
this example:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-terminal"><div class="docs-select-all right" id="sa16553837"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-terminal"><span class="token prompt">$> </span><span class="token command">ndb_mgm</span> <span class="token property">-e</span> <span class="token atrule">"START BACKUP 6 WAIT COMPLETED SNAPSHOTSTART"</span></code></pre>
</div>
<p>
When using
<code class="literal">
START BACKUP
</code>
in this way, you must
specify the backup ID.
</p>
<p>
Cluster backups are created by default in the
<code class="filename">
BACKUP
</code>
subdirectory of the
<a class="link" href="mysql-cluster-ndbd-definition.html#ndbparam-ndbd-datadir">
<code class="literal">
DataDir
</code>
</a>
on each data
node. This can be overridden for one or more data nodes
individually, or for all cluster data nodes in the
<code class="filename">
config.ini
</code>
file using the
<a class="link" href="mysql-cluster-ndbd-definition.html#ndbparam-ndbd-backupdatadir">
<code class="literal">
BackupDataDir
</code>
</a>
configuration parameter. The backup files created for a backup
with a given
<em class="replaceable">
<code>
backup_id
</code>
</em>
are stored in
a subdirectory named
<code class="filename">
BACKUP-
<em class="replaceable">
<code>
backup_id
</code>
</em>
</code>
in the backup directory.
</p>
<p>
<a name="ndbclient-abort-backup">
</a>
<b>
Cancelling backups.
</b>
To cancel or abort a backup that is already in progress,
perform the following steps:
</p>
<div class="orderedlist">
<ol class="orderedlist" type="1">
<li class="listitem">
<p>
Start the management client.
</p>
</li>
<li class="listitem">
<p>
Execute this command:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-ndbmgm"><div class="docs-select-all right" id="sa34595857"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-ndbmgm"><span class="token prompt">ndb_mgm></span> <span class="token keyword">ABORT BACKUP</span> <em class="replaceable">backup_id</em></code></pre>
</div>
<p>
The number
<em class="replaceable">
<code>
backup_id
</code>
</em>
is the
identifier of the backup that was included in the response
of the management client when the backup was started (in the
message
<code class="literal">
Backup
<em class="replaceable">
<code>
backup_id
</code>
</em>
started from node
<em class="replaceable">
<code>
management_node_id
</code>
</em>
</code>
).
</p>
</li>
<li class="listitem">
<p>
The management client acknowledges the abort request with
<code class="literal">
Abort of backup
<em class="replaceable">
<code>
backup_id
</code>
</em>
ordered
</code>
.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
At this point, the management client has not yet received
a response from the cluster data nodes to this request,
and the backup has not yet actually been aborted.
</p>
</div>
</li>
<li class="listitem">
<p>
After the backup has been aborted, the management client
reports this fact in a manner similar to what is shown here:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-ndbmgm"><div class="docs-select-all right" id="sa11844974"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-ndbmgm"><span class="token selector">Node 1:</span> Backup 3 started from 5 has been aborted<span class="token punctuation">.</span>
Error<span class="token operator">:</span> 1321 <span class="token operator">-</span> Backup aborted by user request<span class="token operator">:</span> Permanent error<span class="token operator">:</span> User defined error
<span class="token selector">Node 3:</span> Backup 3 started from 5 has been aborted<span class="token punctuation">.</span>
Error<span class="token operator">:</span> 1323 <span class="token operator">-</span> 1323<span class="token operator">:</span> Permanent error<span class="token operator">:</span> Internal error
<span class="token selector">Node 2:</span> Backup 3 started from 5 has been aborted<span class="token punctuation">.</span>
Error<span class="token operator">:</span> 1323 <span class="token operator">-</span> 1323<span class="token operator">:</span> Permanent error<span class="token operator">:</span> Internal error
<span class="token selector">Node 4:</span> Backup 3 started from 5 has been aborted<span class="token punctuation">.</span>
Error<span class="token operator">:</span> 1323 <span class="token operator">-</span> 1323<span class="token operator">:</span> Permanent error<span class="token operator">:</span> Internal error</code></pre>
</div>
<p>
In this example, we have shown sample output for a cluster
with 4 data nodes, where the sequence number of the backup
to be aborted is
<code class="literal">
3
</code>
, and the management
node to which the cluster management client is connected has
the node ID
<code class="literal">
5
</code>
. The first node to complete
its part in aborting the backup reports that the reason for
the abort was due to a request by the user. (The remaining
nodes report that the backup was aborted due to an
unspecified internal error.)
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
There is no guarantee that the cluster nodes respond to an
<code class="literal">
ABORT BACKUP
</code>
command in any particular
order.
</p>
</div>
<p>
The
<code class="literal">
Backup
<em class="replaceable">
<code>
backup_id
</code>
</em>
started from node
<em class="replaceable">
<code>
management_node_id
</code>
</em>
has been
aborted
</code>
messages mean that the backup has been
terminated and that all files relating to this backup have
been removed from the cluster file system.
</p>
</li>
</ol>
</div>
<p>
It is also possible to abort a backup in progress from a system
shell using this command:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-terminal"><div class="docs-select-all right" id="sa96417901"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-terminal"><span class="token prompt">$> </span><span class="token command">ndb_mgm</span> <span class="token property">-e</span> <span class="token atrule">"ABORT BACKUP <em class="replaceable">backup_id</em>"</span></code></pre>
</div>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
If there is no backup having the ID
<em class="replaceable">
<code>
backup_id
</code>
</em>
running when an
<code class="literal">
ABORT BACKUP
</code>
is issued, the management
client makes no response, nor is it indicated in the cluster
log that an invalid abort command was sent.
</p>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/audit-log-filtering.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="audit-log-filtering">
</a>
8.4.5.7 Audit Log Filtering
</h4>
</div>
</div>
</div>
<a class="indexterm" name="idm46045237322224">
</a>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
For audit log filtering to work as described here, the audit
log plugin
<span class="emphasis">
<em>
and the accompanying audit tables and
functions
</em>
</span>
must be installed. If the plugin is
installed without the accompanying audit tables and functions
needed for rule-based filtering, the plugin operates in legacy
filtering mode, described in
<a class="xref" href="audit-log-legacy-filtering.html" title="8.4.5.10 Legacy Mode Audit Log Filtering">
Section 8.4.5.10, “Legacy Mode Audit Log Filtering”
</a>
. Legacy mode
(deprecated) is filtering behavior as it was prior to MySQL
5.7.13; that is, before the introduction of rule-based
filtering.
</p>
</div>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<a class="xref" href="audit-log-filtering.html#audit-log-filtering-properties" title="Properties of Audit Log Filtering">
Properties of Audit Log Filtering
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="audit-log-filtering.html#audit-log-filtering-function-constraints" title="Constraints on Audit Log Filtering Functions">
Constraints on Audit Log Filtering Functions
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="audit-log-filtering.html#audit-log-filtering-function-usage" title="Using Audit Log Filtering Functions">
Using Audit Log Filtering Functions
</a>
</p>
</li>
</ul>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h5 class="title">
<a name="audit-log-filtering-properties">
</a>
Properties of Audit Log Filtering
</h5>
</div>
</div>
</div>
<p>
The audit log plugin has the capability of controlling logging
of audited events by filtering them:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
Audited events can be filtered using these
characteristics:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<p>
User account
</p>
</li>
<li class="listitem">
<p>
Audit event class
</p>
</li>
<li class="listitem">
<p>
Audit event subclass
</p>
</li>
<li class="listitem">
<p>
Audit event fields such as those that indicate
operation status or SQL statement executed
</p>
</li>
</ul>
</div>
</li>
<li class="listitem">
<p>
Audit filtering is rule based:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<p>
A filter definition creates a set of auditing rules.
Definitions can be configured to include or exclude
events for logging based on the characteristics just
described.
</p>
</li>
<li class="listitem">
<p>
Filter rules have the capability of blocking
(aborting) execution of qualifying events, in addition
to existing capabilities for event logging.
</p>
</li>
<li class="listitem">
<p>
Multiple filters can be defined, and any given filter
can be assigned to any number of user accounts.
</p>
</li>
<li class="listitem">
<p>
It is possible to define a default filter to use with
any user account that has no explicitly assigned
filter.
</p>
</li>
</ul>
</div>
<p>
Audit log filtering is used to implement component
services. To get the optional query statistics available
from that release, you set them up as a filter using the
service component, which implements the services that
write the statistics to the audit log. For instructions to
set this filter up, see
<a class="xref" href="audit-log-logging-configuration.html#audit-log-query-statistics" title="Adding Query Statistics for Outlier Detection">
Adding Query Statistics for Outlier Detection
</a>
.
</p>
<p>
For information about writing filtering rules, see
<a class="xref" href="audit-log-filter-definitions.html" title="8.4.5.8 Writing Audit Log Filter Definitions">
Section 8.4.5.8, “Writing Audit Log Filter Definitions”
</a>
.
</p>
</li>
<li class="listitem">
<p>
Audit filters can be defined and modified using an SQL
interface based on function calls. To display audit
filters, query the
<code class="literal">
mysql.audit_log_filter
</code>
table.
</p>
</li>
<li class="listitem">
<p>
Audit filter definitions are stored in the tables in the
<code class="literal">
mysql
</code>
system database.
</p>
</li>
<li class="listitem">
<p>
Within a given session, the value of the read-only
<a class="link" href="audit-log-reference.html#sysvar_audit_log_filter_id">
<code class="literal">
audit_log_filter_id
</code>
</a>
system variable indicates whether a filter is assigned to
the session.
</p>
</li>
</ul>
</div>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
By default, rule-based audit log filtering logs no auditable
events for any users. To log all auditable events for all
users, use the following statements, which create a simple
filter to enable logging and assign it to the default
account:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa71775112"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">SELECT</span> audit_log_filter_set_filter<span class="token punctuation">(</span><span class="token string">'log_all'</span><span class="token punctuation">,</span> <span class="token string">'{ "filter": { "log": true } }'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">SELECT</span> audit_log_filter_set_user<span class="token punctuation">(</span><span class="token string">'%'</span><span class="token punctuation">,</span> <span class="token string">'log_all'</span><span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
The filter assigned to
<code class="literal">
%
</code>
is used for
connections from any account that has no explicitly assigned
filter (which initially is true for all accounts).
</p>
</div>
<p>
As previously mentioned, the SQL interface for audit filtering
control is function based. The following list briefly
summarizes these functions:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<a class="link" href="audit-log-reference.html#function_audit-log-filter-set-filter">
<code class="literal">
audit_log_filter_set_filter()
</code>
</a>
:
Define a filter.
</p>
</li>
<li class="listitem">
<p>
<a class="link" href="audit-log-reference.html#function_audit-log-filter-remove-filter">
<code class="literal">
audit_log_filter_remove_filter()
</code>
</a>
:
Remove a filter.
</p>
</li>
<li class="listitem">
<p>
<a class="link" href="audit-log-reference.html#function_audit-log-filter-set-user">
<code class="literal">
audit_log_filter_set_user()
</code>
</a>
:
Start filtering a user account.
</p>
</li>
<li class="listitem">
<p>
<a class="link" href="audit-log-reference.html#function_audit-log-filter-remove-user">
<code class="literal">
audit_log_filter_remove_user()
</code>
</a>
:
Stop filtering a user account.
</p>
</li>
<li class="listitem">
<p>
<a class="link" href="audit-log-reference.html#function_audit-log-filter-flush">
<code class="literal">
audit_log_filter_flush()
</code>
</a>
:
Flush manual changes to the filter tables to affect
ongoing filtering.
</p>
</li>
</ul>
</div>
<p>
For usage examples and complete details about the filtering
functions, see
<a class="xref" href="audit-log-filtering.html#audit-log-filtering-function-usage" title="Using Audit Log Filtering Functions">
Using Audit Log Filtering Functions
</a>
, and
<a class="xref" href="audit-log-reference.html#audit-log-routines" title="Audit Log Functions">
Audit Log Functions
</a>
.
</p>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h5 class="title">
<a name="audit-log-filtering-function-constraints">
</a>
Constraints on Audit Log Filtering Functions
</h5>
</div>
</div>
</div>
<p>
Audit log filtering functions are subject to these
constraints:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
To use any filtering function, the
<code class="literal">
audit_log
</code>
plugin must be enabled or an
error occurs. In addition, the audit tables must exist or
an error occurs. To install the
<code class="literal">
audit_log
</code>
plugin and its accompanying
functions and tables, see
<a class="xref" href="audit-log-installation.html" title="8.4.5.2 Installing or Uninstalling MySQL Enterprise Audit">
Section 8.4.5.2, “Installing or Uninstalling MySQL Enterprise Audit”
</a>
.
</p>
</li>
<li class="listitem">
<p>
To use any filtering function, a user must possess the
<a class="link" href="privileges-provided.html#priv_audit-admin">
<code class="literal">
AUDIT_ADMIN
</code>
</a>
<a class="link" href="privileges-provided.html#priv_super">
<code class="literal">
SUPER
</code>
</a>
privilege or an error
occurs. To grant one of these privileges to a user
account, use this statement:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa88120094"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">GRANT</span> <em class="replaceable">privilege</em> <span class="token keyword">ON</span> <span class="token operator">*</span><span class="token punctuation">.</span><span class="token operator">*</span> <span class="token keyword">TO</span> <span class="token keyword"><em class="replaceable">user</em></span><span class="token punctuation">;</span></code></pre>
</div>
<p>
Alternatively, should you prefer to avoid granting the
<a class="link" href="privileges-provided.html#priv_audit-admin">
<code class="literal">
AUDIT_ADMIN
</code>
</a>
or
<a class="link" href="privileges-provided.html#priv_super">
<code class="literal">
SUPER
</code>
</a>
privilege while still
permitting users to access specific filtering functions,
<span class="quote">
“
<span class="quote">
wrapper
</span>
”
</span>
stored programs can be defined.
This technique is described in the context of keyring
functions in
<a class="xref" href="keyring-functions-general-purpose.html#keyring-function-usage" title="Using General-Purpose Keyring Functions">
Using General-Purpose Keyring Functions
</a>
; it
can be adapted for use with filtering functions.
</p>
</li>
<li class="listitem">
<p>
The
<code class="literal">
audit_log
</code>
plugin operates in legacy
mode if it is installed but the accompanying audit tables
and functions are not created. The plugin writes these
messages to the error log at server startup:
</p>
<a class="indexterm" name="idm46045237260608">
</a>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-none"><div class="docs-select-all right" id="sa69320142"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-none">[Warning] Plugin audit_log reported: 'Failed to open the audit log filter tables.'
[Warning] Plugin audit_log reported: 'Audit Log plugin supports a filtering,
which has not been installed yet. Audit Log plugin will run in the legacy
mode, which will be disabled in the next release.'</code></pre>
</div>
<p>
In legacy mode, which is deprecated, filtering can be done
based only on event account or status. For details, see
<a class="xref" href="audit-log-legacy-filtering.html" title="8.4.5.10 Legacy Mode Audit Log Filtering">
Section 8.4.5.10, “Legacy Mode Audit Log Filtering”
</a>
.
</p>
</li>
<li class="listitem">
<p>
It is theoretically possible for a user with sufficient
permissions to mistakenly create an
<span class="quote">
“
<span class="quote">
abort
</span>
”
</span>
item in the audit log filter that prevents themselves and
other administrators from accessing the system. The
<a class="link" href="privileges-provided.html#priv_audit-abort-exempt">
<code class="literal">
AUDIT_ABORT_EXEMPT
</code>
</a>
privilege is available to permit a user account’s
queries to always be executed even if an
<span class="quote">
“
<span class="quote">
abort
</span>
”
</span>
item would block them. Accounts with
this privilege can therefore be used to regain access to a
system following an audit misconfiguration. The query is
still logged in the audit log, but instead of being
rejected, it is permitted due to the privilege.
</p>
<p>
Accounts created with the
<a class="link" href="privileges-provided.html#priv_system-user">
<code class="literal">
SYSTEM_USER
</code>
</a>
privilege have
the
<a class="link" href="privileges-provided.html#priv_audit-abort-exempt">
<code class="literal">
AUDIT_ABORT_EXEMPT
</code>
</a>
privilege assigned automatically when they are created.
The
<a class="link" href="privileges-provided.html#priv_audit-abort-exempt">
<code class="literal">
AUDIT_ABORT_EXEMPT
</code>
</a>
privilege is also assigned to existing accounts with the
<a class="link" href="privileges-provided.html#priv_system-user">
<code class="literal">
SYSTEM_USER
</code>
</a>
privilege when
you carry out an upgrade procedure, if no existing
accounts have that privilege assigned.
</p>
</li>
</ul>
</div>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h5 class="title">
<a name="audit-log-filtering-function-usage">
</a>
Using Audit Log Filtering Functions
</h5>
</div>
</div>
</div>
<p>
Before using the audit log functions, install them according
to the instructions provided in
<a class="xref" href="audit-log-installation.html" title="8.4.5.2 Installing or Uninstalling MySQL Enterprise Audit">
Section 8.4.5.2, “Installing or Uninstalling MySQL Enterprise Audit”
</a>
. The
<a class="link" href="privileges-provided.html#priv_audit-admin">
<code class="literal">
AUDIT_ADMIN
</code>
</a>
or
<a class="link" href="privileges-provided.html#priv_super">
<code class="literal">
SUPER
</code>
</a>
privilege is required to
use any of these functions.
</p>
<p>
The audit log filtering functions enable filtering control by
providing an interface to create, modify, and remove filter
definitions and assign filters to user accounts.
</p>
<p>
Filter definitions are
<a class="link" href="json.html" title="13.5 The JSON Data Type">
<code class="literal">
JSON
</code>
</a>
values. For information about using
<a class="link" href="json.html" title="13.5 The JSON Data Type">
<code class="literal">
JSON
</code>
</a>
data in MySQL, see
<a class="xref" href="json.html" title="13.5 The JSON Data Type">
Section 13.5, “The JSON Data Type”
</a>
. This section shows some simple filter
definitions. For more information about filter definitions,
see
<a class="xref" href="audit-log-filter-definitions.html" title="8.4.5.8 Writing Audit Log Filter Definitions">
Section 8.4.5.8, “Writing Audit Log Filter Definitions”
</a>
.
</p>
<p>
When a connection arrives, the audit log plugin determines
which filter to use for the new session by searching for the
user account name in the current filter assignments:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
If a filter is assigned to the user, the audit log uses
that filter.
</p>
</li>
<li class="listitem">
<p>
Otherwise, if no user-specific filter assignment exists,
but there is a filter assigned to the default account
(
<code class="literal">
%
</code>
), the audit log uses the default
filter.
</p>
</li>
<li class="listitem">
<p>
Otherwise, the audit log selects no audit events from the
session for processing.
</p>
</li>
</ul>
</div>
<p>
If a change-user operation occurs during a session (see
<a class="ulink" href="/doc/c-api/8.4/en/mysql-change-user.html" target="_top">
mysql_change_user()
</a>
), filter assignment for
the session is updated using the same rules but for the new
user.
</p>
<p>
By default, no accounts have a filter assigned, so no
processing of auditable events occurs for any account.
</p>
<p>
Suppose that you want to change the default to be to log only
connection-related activity (for example, to see connect,
change-user, and disconnect events, but not the SQL statements
users execute while connected). To achieve this, define a
filter (shown here named
<code class="literal">
log_conn_events
</code>
)
that enables logging only of events in the
<code class="literal">
connection
</code>
class, and assign that filter to
the default account, represented by the
<code class="literal">
%
</code>
account name:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa54485022"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">SET</span> <span class="token variable">@f</span> <span class="token operator">=</span> <span class="token string">'{ "filter": { "class": { "name": "connection" } } }'</span><span class="token punctuation">;</span>
<span class="token keyword">SELECT</span> audit_log_filter_set_filter<span class="token punctuation">(</span><span class="token string">'log_conn_events'</span><span class="token punctuation">,</span> <span class="token variable">@f</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">SELECT</span> audit_log_filter_set_user<span class="token punctuation">(</span><span class="token string">'%'</span><span class="token punctuation">,</span> <span class="token string">'log_conn_events'</span><span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
Now the audit log uses this default account filter for
connections from any account that has no explicitly defined
filter.
</p>
<p>
To assign a filter explicitly to a particular user account or
accounts, define the filter, then assign it to the relevant
accounts:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa37738113"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">SELECT</span> audit_log_filter_set_filter<span class="token punctuation">(</span><span class="token string">'log_all'</span><span class="token punctuation">,</span> <span class="token string">'{ "filter": { "log": true } }'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">SELECT</span> audit_log_filter_set_user<span class="token punctuation">(</span><span class="token string">'user1@localhost'</span><span class="token punctuation">,</span> <span class="token string">'log_all'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">SELECT</span> audit_log_filter_set_user<span class="token punctuation">(</span><span class="token string">'user2@localhost'</span><span class="token punctuation">,</span> <span class="token string">'log_all'</span><span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
Now full logging is enabled for
<code class="literal">
user1@localhost
</code>
and
<code class="literal">
user2@localhost
</code>
. Connections from other
accounts continue to be filtered using the default account
filter.
</p>
<p>
To disassociate a user account from its current filter, either
unassign the filter or assign a different filter:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
To unassign the filter from the user account:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa72099046"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">SELECT</span> audit_log_filter_remove_user<span class="token punctuation">(</span><span class="token string">'user1@localhost'</span><span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
Filtering of current sessions for the account remains
unaffected. Subsequent connections from the account are
filtered using the default account filter if there is one,
and are not logged otherwise.
</p>
</li>
<li class="listitem">
<p>
To assign a different filter to the user account:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa3929482"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">SELECT</span> audit_log_filter_set_filter<span class="token punctuation">(</span><span class="token string">'log_nothing'</span><span class="token punctuation">,</span> <span class="token string">'{ "filter": { "log": false } }'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">SELECT</span> audit_log_filter_set_user<span class="token punctuation">(</span><span class="token string">'user1@localhost'</span><span class="token punctuation">,</span> <span class="token string">'log_nothing'</span><span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
Filtering of current sessions for the account remains
unaffected. Subsequent connections from the account are
filtered using the new filter. For the filter shown here,
that means no logging for new connections from
<code class="literal">
user1@localhost
</code>
.
</p>
</li>
</ul>
</div>
<p>
For audit log filtering, user name and host name comparisons
are case-sensitive. This differs from comparisons for
privilege checking, for which host name comparisons are not
case-sensitive.
</p>
<p>
To remove a filter, do this:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa19280512"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">SELECT</span> audit_log_filter_remove_filter<span class="token punctuation">(</span><span class="token string">'log_nothing'</span><span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
Removing a filter also unassigns it from any users to whom it
is assigned, including any current sessions for those users.
</p>
<p>
The filtering functions just described affect audit filtering
immediately and update the audit log tables in the
<code class="literal">
mysql
</code>
system database that store filters
and user accounts (see
<a class="xref" href="audit-log-reference.html#audit-log-tables" title="Audit Log Tables">
Audit Log Tables
</a>
). It
is also possible to modify the audit log tables directly using
statements such as
<a class="link" href="insert.html" title="15.2.7 INSERT Statement">
<code class="literal">
INSERT
</code>
</a>
,
<a class="link" href="update.html" title="15.2.17 UPDATE Statement">
<code class="literal">
UPDATE
</code>
</a>
, and
<a class="link" href="delete.html" title="15.2.2 DELETE Statement">
<code class="literal">
DELETE
</code>
</a>
, but such changes do not
affect filtering immediately. To flush your changes and make
them operational, call
<a class="link" href="audit-log-reference.html#function_audit-log-filter-flush">
<code class="literal">
audit_log_filter_flush()
</code>
</a>
:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa69356782"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">SELECT</span> audit_log_filter_flush<span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
<div class="warning" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Warning
</div>
<p>
<a class="link" href="audit-log-reference.html#function_audit-log-filter-flush">
<code class="literal">
audit_log_filter_flush()
</code>
</a>
should be used only after modifying the audit tables
directly, to force reloading all filters. Otherwise, this
function should be avoided. It is, in effect, a simplified
version of unloading and reloading the
<code class="literal">
audit_log
</code>
plugin with
<a class="link" href="uninstall-plugin.html" title="15.7.4.6 UNINSTALL PLUGIN Statement">
<code class="literal">
UNINSTALL PLUGIN
</code>
</a>
plus
<a class="link" href="install-plugin.html" title="15.7.4.4 INSTALL PLUGIN Statement">
<code class="literal">
INSTALL PLUGIN
</code>
</a>
.
</p>
<p>
<a class="link" href="audit-log-reference.html#function_audit-log-filter-flush">
<code class="literal">
audit_log_filter_flush()
</code>
</a>
affects all current sessions and detaches them from their
previous filters. Current sessions are no longer logged
unless they disconnect and reconnect, or execute a
change-user operation.
</p>
</div>
<p>
To determine whether a filter is assigned to the current
session, check the session value of the read-only
<a class="link" href="audit-log-reference.html#sysvar_audit_log_filter_id">
<code class="literal">
audit_log_filter_id
</code>
</a>
system
variable. If the value is 0, no filter is assigned. A nonzero
value indicates the internally maintained ID of the assigned
filter:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa22017846"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token variable">@@audit_log_filter_id</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> @@audit_log_filter_id <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> 2 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span></code></pre>
</div>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/explain.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="explain">
</a>
15.8.2 EXPLAIN Statement
</h3>
</div>
</div>
</div>
<a class="indexterm" name="idm46045168200480">
</a>
<a class="indexterm" name="idm46045168199408">
</a>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa17947713"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql">{<span class="token keyword">EXPLAIN</span> <span class="token operator">|</span> <span class="token keyword">DESCRIBE</span> <span class="token operator">|</span> <span class="token keyword">DESC</span>}
<em class="replaceable">tbl_name</em> <span class="token punctuation">[</span><em class="replaceable">col_name</em> <span class="token operator">|</span> <em class="replaceable">wild</em><span class="token punctuation">]</span>
{<span class="token keyword">EXPLAIN</span> <span class="token operator">|</span> <span class="token keyword">DESCRIBE</span> <span class="token operator">|</span> <span class="token keyword">DESC</span>}
<span class="token punctuation">[</span><em class="replaceable">explain_type</em><span class="token punctuation">]</span> <span class="token punctuation">[</span><span class="token keyword">INTO</span> <em class="replaceable">variable</em><span class="token punctuation">]</span>
{<span class="token punctuation">[</span><em class="replaceable">schema_spec</em><span class="token punctuation">]</span> <em class="replaceable">explainable_stmt</em> <span class="token operator">|</span> <span class="token keyword">FOR</span> <span class="token keyword">CONNECTION</span> <em class="replaceable">connection_id</em>}
{<span class="token keyword">EXPLAIN</span> <span class="token operator">|</span> <span class="token keyword">DESCRIBE</span> <span class="token operator">|</span> <span class="token keyword">DESC</span>} <span class="token keyword">ANALYZE</span> <span class="token punctuation">[</span><span class="token keyword">FORMAT</span> <span class="token operator">=</span> <span class="token keyword">TREE</span><span class="token punctuation">]</span> <span class="token punctuation">[</span><em class="replaceable">schema_spec</em><span class="token punctuation">]</span> <em class="replaceable">select_statement</em>
<em class="replaceable">explain_type</em>: {
<span class="token keyword">FORMAT</span> <span class="token operator">=</span> <em class="replaceable">format_name</em>
}
<em class="replaceable">format_name</em>: {
<span class="token keyword">TRADITIONAL</span>
<span class="token operator">|</span> <span class="token datatype">JSON</span>
<span class="token operator">|</span> <span class="token keyword">TREE</span>
}
<em class="replaceable">explainable_stmt</em>: {
<span class="token keyword">SELECT</span> statement
<span class="token operator">|</span> <span class="token keyword">TABLE</span> statement
<span class="token operator">|</span> <span class="token keyword">DELETE</span> statement
<span class="token operator">|</span> <span class="token keyword">INSERT</span> statement
<span class="token operator">|</span> <span class="token keyword">REPLACE</span> statement
<span class="token operator">|</span> <span class="token keyword">UPDATE</span> statement
}
<em class="replaceable">schema_spec</em>:
<span class="token keyword">FOR</span> {<span class="token keyword">SCHEMA</span> <span class="token operator">|</span> <span class="token keyword">DATABASE</span>} <span class="token keyword"><em class="replaceable">schema_name</em></span></code></pre>
</div>
<p>
The
<a class="link" href="describe.html" title="15.8.1 DESCRIBE Statement">
<code class="literal">
DESCRIBE
</code>
</a>
and
<a class="link" href="explain.html" title="15.8.2 EXPLAIN Statement">
<code class="literal">
EXPLAIN
</code>
</a>
statements are synonyms. In
practice, the
<a class="link" href="describe.html" title="15.8.1 DESCRIBE Statement">
<code class="literal">
DESCRIBE
</code>
</a>
keyword is
more often used to obtain information about table structure,
whereas
<a class="link" href="explain.html" title="15.8.2 EXPLAIN Statement">
<code class="literal">
EXPLAIN
</code>
</a>
is used to obtain a
query execution plan (that is, an explanation of how MySQL would
execute a query).
</p>
<p>
The following discussion uses the
<a class="link" href="describe.html" title="15.8.1 DESCRIBE Statement">
<code class="literal">
DESCRIBE
</code>
</a>
and
<a class="link" href="explain.html" title="15.8.2 EXPLAIN Statement">
<code class="literal">
EXPLAIN
</code>
</a>
keywords in accordance with
those uses, but the MySQL parser treats them as completely
synonymous.
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<a class="xref" href="explain.html#explain-table-structure" title="Obtaining Table Structure Information">
Obtaining Table Structure Information
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="explain.html#explain-execution-plan" title="Obtaining Execution Plan Information">
Obtaining Execution Plan Information
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="explain.html#explain-analyze" title="Obtaining Information with EXPLAIN ANALYZE">
Obtaining Information with EXPLAIN ANALYZE
</a>
</p>
</li>
</ul>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h4 class="title">
<a name="explain-table-structure">
</a>
Obtaining Table Structure Information
</h4>
</div>
</div>
</div>
<p>
<a class="link" href="describe.html" title="15.8.1 DESCRIBE Statement">
<code class="literal">
DESCRIBE
</code>
</a>
provides information
about the columns in a table:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa50605938"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">DESCRIBE</span> City<span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> Field <span class="token punctuation">|</span> Type <span class="token punctuation">|</span> Null <span class="token punctuation">|</span> Key <span class="token punctuation">|</span> Default <span class="token punctuation">|</span> Extra <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> Id <span class="token punctuation">|</span> int(11) <span class="token punctuation">|</span> NO <span class="token punctuation">|</span> PRI <span class="token punctuation">|</span> NULL <span class="token punctuation">|</span> auto_increment <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> Name <span class="token punctuation">|</span> char(35) <span class="token punctuation">|</span> NO <span class="token punctuation">|</span> <span class="token punctuation">|</span> <span class="token punctuation">|</span> <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> Country <span class="token punctuation">|</span> char(3) <span class="token punctuation">|</span> NO <span class="token punctuation">|</span> UNI <span class="token punctuation">|</span> <span class="token punctuation">|</span> <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> District <span class="token punctuation">|</span> char(20) <span class="token punctuation">|</span> YES <span class="token punctuation">|</span> MUL <span class="token punctuation">|</span> <span class="token punctuation">|</span> <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> Population <span class="token punctuation">|</span> int(11) <span class="token punctuation">|</span> NO <span class="token punctuation">|</span> <span class="token punctuation">|</span> 0 <span class="token punctuation">|</span> <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span></code></pre>
</div>
<p>
<a class="link" href="describe.html" title="15.8.1 DESCRIBE Statement">
<code class="literal">
DESCRIBE
</code>
</a>
is a shortcut for
<a class="link" href="show-columns.html" title="15.7.7.6 SHOW COLUMNS Statement">
<code class="literal">
SHOW COLUMNS
</code>
</a>
. These statements
also display information for views. The description for
<a class="link" href="show-columns.html" title="15.7.7.6 SHOW COLUMNS Statement">
<code class="literal">
SHOW COLUMNS
</code>
</a>
provides more
information about the output columns. See
<a class="xref" href="show-columns.html" title="15.7.7.6 SHOW COLUMNS Statement">
Section 15.7.7.6, “SHOW COLUMNS Statement”
</a>
.
</p>
<p>
By default,
<a class="link" href="describe.html" title="15.8.1 DESCRIBE Statement">
<code class="literal">
DESCRIBE
</code>
</a>
displays
information about all columns in the table.
<em class="replaceable">
<code>
col_name
</code>
</em>
, if given, is the name of a
column in the table. In this case, the statement displays
information only for the named column.
<em class="replaceable">
<code>
wild
</code>
</em>
, if given, is a pattern string.
It can contain the SQL
<code class="literal">
%
</code>
and
<code class="literal">
_
</code>
wildcard characters. In this case, the
statement displays output only for the columns with names
matching the string. There is no need to enclose the string
within quotation marks unless it contains spaces or other
special characters.
</p>
<a class="indexterm" name="idm46045168158464">
</a>
<a class="indexterm" name="idm46045168157392">
</a>
<p>
The
<a class="link" href="describe.html" title="15.8.1 DESCRIBE Statement">
<code class="literal">
DESCRIBE
</code>
</a>
statement is
provided for compatibility with Oracle.
</p>
<p>
The
<a class="link" href="show-create-table.html" title="15.7.7.11 SHOW CREATE TABLE Statement">
<code class="literal">
SHOW CREATE TABLE
</code>
</a>
,
<a class="link" href="show-table-status.html" title="15.7.7.38 SHOW TABLE STATUS Statement">
<code class="literal">
SHOW TABLE STATUS
</code>
</a>
, and
<a class="link" href="show-index.html" title="15.7.7.23 SHOW INDEX Statement">
<code class="literal">
SHOW INDEX
</code>
</a>
statements also
provide information about tables. See
<a class="xref" href="show.html" title="15.7.7 SHOW Statements">
Section 15.7.7, “SHOW Statements”
</a>
.
</p>
<p>
The
<a class="link" href="server-system-variables.html#sysvar_explain_format">
<code class="literal">
explain_format
</code>
</a>
system
variable has no effect on the output of
<code class="literal">
EXPLAIN
</code>
when used to obtain information about
table columns.
</p>
<p>
</p>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h4 class="title">
<a name="explain-execution-plan">
</a>
Obtaining Execution Plan Information
</h4>
</div>
</div>
</div>
<p>
The
<a class="link" href="explain.html" title="15.8.2 EXPLAIN Statement">
<code class="literal">
EXPLAIN
</code>
</a>
statement provides
information about how MySQL executes statements:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<a class="link" href="explain.html" title="15.8.2 EXPLAIN Statement">
<code class="literal">
EXPLAIN
</code>
</a>
works with
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT
</code>
</a>
,
<a class="link" href="delete.html" title="15.2.2 DELETE Statement">
<code class="literal">
DELETE
</code>
</a>
,
<a class="link" href="insert.html" title="15.2.7 INSERT Statement">
<code class="literal">
INSERT
</code>
</a>
,
<a class="link" href="replace.html" title="15.2.12 REPLACE Statement">
<code class="literal">
REPLACE
</code>
</a>
,
<a class="link" href="update.html" title="15.2.17 UPDATE Statement">
<code class="literal">
UPDATE
</code>
</a>
, and
<a class="link" href="table.html" title="15.2.16 TABLE Statement">
<code class="literal">
TABLE
</code>
</a>
statements.
</p>
</li>
<li class="listitem">
<p>
When
<a class="link" href="explain.html" title="15.8.2 EXPLAIN Statement">
<code class="literal">
EXPLAIN
</code>
</a>
is used with an
explainable statement, MySQL displays information from the
optimizer about the statement execution plan. That is, MySQL
explains how it would process the statement, including
information about how tables are joined and in which order.
For information about using
<a class="link" href="explain.html" title="15.8.2 EXPLAIN Statement">
<code class="literal">
EXPLAIN
</code>
</a>
to obtain execution
plan information, see
<a class="xref" href="explain-output.html" title="10.8.2 EXPLAIN Output Format">
Section 10.8.2, “EXPLAIN Output Format”
</a>
.
</p>
</li>
<li class="listitem">
<p>
When
<a class="link" href="explain.html" title="15.8.2 EXPLAIN Statement">
<code class="literal">
EXPLAIN
</code>
</a>
is used with
<code class="literal">
FOR CONNECTION
<em class="replaceable">
<code>
connection_id
</code>
</em>
</code>
rather
than an explainable statement, it displays the execution
plan for the statement executing in the named connection.
See
<a class="xref" href="explain-for-connection.html" title="10.8.4 Obtaining Execution Plan Information for a Named Connection">
Section 10.8.4, “Obtaining Execution Plan Information for a Named Connection”
</a>
.
</p>
</li>
<li class="listitem">
<p>
For explainable statements,
<a class="link" href="explain.html" title="15.8.2 EXPLAIN Statement">
<code class="literal">
EXPLAIN
</code>
</a>
produces additional
execution plan information that can be displayed using
<a class="link" href="show-warnings.html" title="15.7.7.42 SHOW WARNINGS Statement">
<code class="literal">
SHOW WARNINGS
</code>
</a>
. See
<a class="xref" href="explain-extended.html" title="10.8.3 Extended EXPLAIN Output Format">
Section 10.8.3, “Extended EXPLAIN Output Format”
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a class="link" href="explain.html" title="15.8.2 EXPLAIN Statement">
<code class="literal">
EXPLAIN
</code>
</a>
is useful for
examining queries involving partitioned tables. See
<a class="xref" href="partitioning-info.html" title="26.3.5 Obtaining Information About Partitions">
Section 26.3.5, “Obtaining Information About Partitions”
</a>
.
</p>
</li>
<li class="listitem">
<p>
The
<code class="literal">
FORMAT
</code>
option can be used to select
the output format.
<code class="literal">
TRADITIONAL
</code>
presents
the output in tabular format. This is the default if no
<code class="literal">
FORMAT
</code>
option is present.
<code class="literal">
JSON
</code>
format displays the information in
JSON format.
<code class="literal">
TREE
</code>
provides tree-like
output with more precise descriptions of query handling than
the
<code class="literal">
TRADITIONAL
</code>
format; it is the only
format which shows hash join usage (see
<a class="xref" href="hash-joins.html" title="10.2.1.4 Hash Join Optimization">
Section 10.2.1.4, “Hash Join Optimization”
</a>
) and is always used for
<code class="literal">
EXPLAIN ANALYZE
</code>
.
</p>
<p>
In MySQL 8.4, the default output format used by
<code class="literal">
EXPLAIN
</code>
(that is, when it has no
<code class="literal">
FORMAT
</code>
option) is determined by the value
of the
<a class="link" href="server-system-variables.html#sysvar_explain_format">
<code class="literal">
explain_format
</code>
</a>
system variable. The precise effects of this variable are
described later in this section.
</p>
<p>
MySQL 8.4 supports an additional
<code class="literal">
INTO
</code>
option with
<code class="literal">
EXPLAIN
FORMAT=JSON
</code>
, which enables saving the JSON
formatted output into a user variable, like this:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa18363959"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">EXPLAIN</span> <span class="token keyword">FORMAT</span><span class="token operator">=</span><span class="token datatype">JSON</span> <span class="token keyword">INTO</span> <span class="token variable">@myselect</span>
<span class="token prompt"> -></span> <span class="token keyword">SELECT</span> <span class="token keyword">name</span> <span class="token keyword">FROM</span> a <span class="token keyword">WHERE</span> id <span class="token operator">=</span> <span class="token number">2</span><span class="token punctuation">;</span>
<span class="token output">Query OK, 0 rows affected (0.00 sec)</span>
<span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token variable">@myselect</span>\G
<span class="token output"><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span> 1. row <span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span>
@myex<span class="token punctuation">:</span> {
"query_block"<span class="token punctuation">:</span> {
"select_id"<span class="token punctuation">:</span> 1,
"cost_info"<span class="token punctuation">:</span> {
"query_cost"<span class="token punctuation">:</span> "1.00"
},
"table"<span class="token punctuation">:</span> {
"table_name"<span class="token punctuation">:</span> "a",
"access_type"<span class="token punctuation">:</span> "const",
"possible_keys"<span class="token punctuation">:</span> [
"PRIMARY"
],
"key"<span class="token punctuation">:</span> "PRIMARY",
"used_key_parts"<span class="token punctuation">:</span> [
"id"
],
"key_length"<span class="token punctuation">:</span> "4",
"ref"<span class="token punctuation">:</span> [
"const"
],
"rows_examined_per_scan"<span class="token punctuation">:</span> 1,
"rows_produced_per_join"<span class="token punctuation">:</span> 1,
"filtered"<span class="token punctuation">:</span> "100.00",
"cost_info"<span class="token punctuation">:</span> {
"read_cost"<span class="token punctuation">:</span> "0.00",
"eval_cost"<span class="token punctuation">:</span> "0.10",
"prefix_cost"<span class="token punctuation">:</span> "0.00",
"data_read_per_join"<span class="token punctuation">:</span> "408"
},
"used_columns"<span class="token punctuation">:</span> [
"id",
"name"
]
}
}
}
</span><span class="token output">1 row in set (0.00 sec)</span></code></pre>
</div>
<p>
This works with any explainable statement
(
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT
</code>
</a>
,
<a class="link" href="table.html" title="15.2.16 TABLE Statement">
<code class="literal">
TABLE
</code>
</a>
,
<a class="link" href="insert.html" title="15.2.7 INSERT Statement">
<code class="literal">
INSERT
</code>
</a>
,
<a class="link" href="update.html" title="15.2.17 UPDATE Statement">
<code class="literal">
UPDATE
</code>
</a>
,
<a class="link" href="replace.html" title="15.2.12 REPLACE Statement">
<code class="literal">
REPLACE
</code>
</a>
, or
<a class="link" href="delete.html" title="15.2.2 DELETE Statement">
<code class="literal">
DELETE
</code>
</a>
). Examples using
<code class="literal">
UPDATE
</code>
and
<code class="literal">
DELETE
</code>
statements are shown here:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa55811252"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">EXPLAIN</span> <span class="token keyword">FORMAT</span><span class="token operator">=</span><span class="token datatype">JSON</span> <span class="token keyword">INTO</span> <span class="token variable">@myupdate</span>
<span class="token prompt"> -></span> <span class="token keyword">UPDATE</span> a <span class="token keyword">SET</span> name2 <span class="token operator">=</span> <span class="token string">"garcia"</span> <span class="token keyword">WHERE</span> id <span class="token operator">=</span> <span class="token number">3</span><span class="token punctuation">;</span>
<span class="token output">Query OK, 0 rows affected (0.00 sec)</span>
<span class="token prompt">mysql></span> <span class="token keyword">EXPLAIN</span> <span class="token keyword">FORMAT</span><span class="token operator">=</span><span class="token datatype">JSON</span> <span class="token keyword">INTO</span> <span class="token variable">@mydelete</span>
<span class="token prompt"> -></span> <span class="token keyword">DELETE</span> <span class="token keyword">FROM</span> a <span class="token keyword">WHERE</span> name1 <span class="token operator">LIKE</span> <span class="token string">'%e%'</span><span class="token punctuation">;</span>
<span class="token output">Query OK, 0 rows affected (0.00 sec)</span>
<span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token variable">@myupdate</span><span class="token punctuation">,</span> <span class="token variable">@mydelete</span>\G
<span class="token output"><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span> 1. row <span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span>
@myupdate<span class="token punctuation">:</span> {
"query_block"<span class="token punctuation">:</span> {
"select_id"<span class="token punctuation">:</span> 1,
"table"<span class="token punctuation">:</span> {
"update"<span class="token punctuation">:</span> true,
"table_name"<span class="token punctuation">:</span> "a",
"access_type"<span class="token punctuation">:</span> "range",
"possible_keys"<span class="token punctuation">:</span> [
"PRIMARY"
],
"key"<span class="token punctuation">:</span> "PRIMARY",
"used_key_parts"<span class="token punctuation">:</span> [
"id"
],
"key_length"<span class="token punctuation">:</span> "4",
"ref"<span class="token punctuation">:</span> [
"const"
],
"rows_examined_per_scan"<span class="token punctuation">:</span> 1,
"filtered"<span class="token punctuation">:</span> "100.00",
"attached_condition"<span class="token punctuation">:</span> "(`db`.`a`.`id` = 3)"
}
}
}
@mydelete<span class="token punctuation">:</span> {
"query_block"<span class="token punctuation">:</span> {
"select_id"<span class="token punctuation">:</span> 1,
"table"<span class="token punctuation">:</span> {
"delete"<span class="token punctuation">:</span> true,
"table_name"<span class="token punctuation">:</span> "a",
"access_type"<span class="token punctuation">:</span> "ALL",
"rows_examined_per_scan"<span class="token punctuation">:</span> 2,
"filtered"<span class="token punctuation">:</span> "100.00",
"attached_condition"<span class="token punctuation">:</span> "(`db`.`a`.`name1` like '%e%')"
}
}
}
</span><span class="token output">1 row in set (0.00 sec)</span></code></pre>
</div>
<p>
You can work with this value using MySQL JSON functions as
you would with any other JSON value, as in these examples
using
<a class="link" href="json-search-functions.html#function_json-extract">
<code class="literal">
JSON_EXTRACT()
</code>
</a>
:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa27194678"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token function">JSON_EXTRACT</span><span class="token punctuation">(</span><span class="token variable">@myselect</span><span class="token punctuation">,</span> <span class="token string">"$.query_block.table.key"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> JSON_EXTRACT(@myselect, "$.query_block.table.key") <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> "PRIMARY" <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output">1 row in set (0.01 sec)</span>
<span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token function">JSON_EXTRACT</span><span class="token punctuation">(</span><span class="token variable">@myupdate</span><span class="token punctuation">,</span> <span class="token string">"$.query_block.table.access_type"</span><span class="token punctuation">)</span> <span class="token keyword">AS</span> U_acc<span class="token punctuation">,</span>
<span class="token prompt"> -></span> <span class="token function">JSON_EXTRACT</span><span class="token punctuation">(</span><span class="token variable">@mydelete</span><span class="token punctuation">,</span> <span class="token string">"$.query_block.table.access_type"</span><span class="token punctuation">)</span> <span class="token keyword">AS</span> D_acc<span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> U_acc <span class="token punctuation">|</span> D_acc <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> "range" <span class="token punctuation">|</span> "ALL" <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output">1 row in set (0.00 sec)</span></code></pre>
</div>
<p>
For complex statements, the JSON output can be quite large;
in particular, it can be difficult when reading it to pair
the closing bracket and opening brackets; to cause the JSON
structure's key, if it has one, to be repeated near the
closing bracket, set
<a class="link" href="server-system-variables.html#sysvar_end_markers_in_json">
<code class="literal">
end_markers_in_json=ON
</code>
</a>
. You
should be aware that while this makes the output easier to
read, it also renders the JSON invalid, causing JSON
functions to raise an error.
</p>
<p>
See also
<a class="xref" href="json-functions.html" title="14.17 JSON Functions">
Section 14.17, “JSON Functions”
</a>
.
</p>
<p>
Trying to use an
<code class="literal">
INTO
</code>
clause without
explicitly including
<code class="literal">
FORMAT=JSON
</code>
causes
<code class="literal">
EXPLAIN
</code>
to be rejected with
<a class="ulink" href="/doc/mysql-errors/8.4/en/server-error-reference.html#error_er_explain_into_implicit_format_not_supported" target="_top">
<code class="literal">
ER_EXPLAIN_INTO_IMPLICIT_FORMAT_NOT_SUPPORTED
</code>
</a>
.
This is true regardless of the current value of the
<a class="link" href="server-system-variables.html#sysvar_explain_format">
<code class="literal">
explain_format
</code>
</a>
system
variable.
</p>
<p>
The
<code class="literal">
INTO
</code>
clause is not supported with
<code class="literal">
FOR CONNECTION
</code>
.
</p>
<p>
<code class="literal">
INTO
</code>
is also not supported with
<code class="literal">
EXPLAIN ANALYZE
</code>
when
<a class="link" href="server-system-variables.html#sysvar_explain_json_format_version">
<code class="literal">
explain_json_format_version=1
</code>
</a>
.
</p>
<div class="important" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Important
</div>
<p>
If, for any reason, the statement to be analyzed is
rejected, the user variable is not updated.
</p>
</div>
</li>
<li class="listitem">
<p>
MySQL 8.4 supports a
<code class="literal">
FOR
SCHEMA
</code>
clause, which causes
<code class="literal">
EXPLAIN
</code>
to behave as if the statement to
be analyzed had been executed in the named database;
<code class="literal">
FOR DATABASE
</code>
is supported as a synonym. A
simple example of use is shown here:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa32954117"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">USE</span> b<span class="token punctuation">;</span>
<span class="token keyword">Database</span> <span class="token keyword">changed</span>
<span class="token prompt">mysql></span> <span class="token keyword">CREATE</span> <span class="token keyword">SCHEMA</span> s1<span class="token punctuation">;</span>
<span class="token output">Query OK, 1 row affected (0.01 sec)</span>
<span class="token prompt">mysql></span> <span class="token keyword">CREATE</span> <span class="token keyword">SCHEMA</span> s2<span class="token punctuation">;</span>
<span class="token output">Query OK, 1 row affected (0.01 sec)</span>
<span class="token prompt">mysql></span> <span class="token keyword">USE</span> s1<span class="token punctuation">;</span>
<span class="token keyword">Database</span> <span class="token keyword">changed</span>
<span class="token prompt">mysql></span> <span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> t <span class="token punctuation">(</span>c1 <span class="token datatype">INT</span> <span class="token operator">NOT</span> <span class="token boolean">NULL</span> <span class="token keyword">AUTO_INCREMENT</span> <span class="token keyword">PRIMARY</span> <span class="token keyword">KEY</span><span class="token punctuation">,</span> c2 <span class="token datatype">INT</span> <span class="token operator">NOT</span> <span class="token boolean">NULL</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token output">Query OK, 0 rows affected (0.04 sec)</span>
<span class="token prompt">mysql></span> <span class="token keyword">USE</span> s2<span class="token punctuation">;</span>
<span class="token keyword">Database</span> <span class="token keyword">changed</span>
<span class="token prompt">mysql></span> <span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> t <span class="token punctuation">(</span>c1 <span class="token datatype">INT</span> <span class="token operator">NOT</span> <span class="token boolean">NULL</span> <span class="token keyword">AUTO_INCREMENT</span> <span class="token keyword">PRIMARY</span> <span class="token keyword">KEY</span><span class="token punctuation">,</span> c2 <span class="token datatype">INT</span> <span class="token operator">NOT</span> <span class="token boolean">NULL</span><span class="token punctuation">,</span> <span class="token keyword">KEY</span> i1 <span class="token punctuation">(</span>c2<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token output">Query OK, 0 rows affected (0.04 sec)</span>
<span class="token prompt">mysql></span> <span class="token keyword">USE</span> b<span class="token punctuation">;</span>
<span class="token keyword">Database</span> <span class="token keyword">changed</span>
<span class="token prompt">mysql></span> <span class="token keyword">EXPLAIN</span> <span class="token keyword">FORMAT</span><span class="token operator">=</span><span class="token keyword">TREE</span> <span class="token keyword">FOR</span> <span class="token keyword">SCHEMA</span> s1 <span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> t <span class="token keyword">WHERE</span> c2 <span class="token operator">></span> <span class="token number">50</span>\G
<span class="token output"><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span> 1. row <span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span>
EXPLAIN<span class="token punctuation">:</span> -> Filter<span class="token punctuation">:</span> (t.c2 > 50) (cost=0.35 rows=1)</span>
<span class="token prompt"> -></span> <span class="token keyword">Table</span> scan <span class="token keyword">on</span> t <span class="token punctuation">(</span>cost<span class="token operator">=</span><span class="token number">0.35</span> <span class="token keyword">rows</span><span class="token operator">=</span><span class="token number">1</span><span class="token punctuation">)</span>
<span class="token output">1 row in set (0.00 sec)</span>
<span class="token prompt">mysql></span> <span class="token keyword">EXPLAIN</span> <span class="token keyword">FORMAT</span><span class="token operator">=</span><span class="token keyword">TREE</span> <span class="token keyword">FOR</span> <span class="token keyword">SCHEMA</span> s2 <span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> t <span class="token keyword">WHERE</span> c2 <span class="token operator">></span> <span class="token number">50</span>\G
<span class="token output"><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span> 1. row <span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span>
EXPLAIN<span class="token punctuation">:</span> -> Filter<span class="token punctuation">:</span> (t.c2 > 50) (cost=0.35 rows=1)</span>
<span class="token prompt"> -></span> Covering <span class="token keyword">index</span> scan <span class="token keyword">on</span> t <span class="token keyword">using</span> i1 <span class="token punctuation">(</span>cost<span class="token operator">=</span><span class="token number">0.35</span> <span class="token keyword">rows</span><span class="token operator">=</span><span class="token number">1</span><span class="token punctuation">)</span>
<span class="token output">1 row in set (0.00 sec)</span></code></pre>
</div>
<p>
If the database does not exist, the statement is rejected
with
<a class="ulink" href="/doc/mysql-errors/8.4/en/server-error-reference.html#error_er_bad_db_error" target="_top">
<code class="literal">
ER_BAD_DB_ERROR
</code>
</a>
. If the
user does not have the necessary privileges to run the
statement, it is rejected with
<a class="ulink" href="/doc/mysql-errors/8.4/en/server-error-reference.html#error_er_dbaccess_denied_error" target="_top">
<code class="literal">
ER_DBACCESS_DENIED_ERROR
</code>
</a>
.
</p>
<p>
<code class="literal">
FOR SCHEMA
</code>
is not compatible with
<code class="literal">
FOR CONNECTION
</code>
.
</p>
</li>
</ul>
</div>
<p>
<a class="link" href="explain.html" title="15.8.2 EXPLAIN Statement">
<code class="literal">
EXPLAIN
</code>
</a>
requires the same
privileges required to execute the explained statement.
Additionally,
<a class="link" href="explain.html" title="15.8.2 EXPLAIN Statement">
<code class="literal">
EXPLAIN
</code>
</a>
also
requires the
<a class="link" href="privileges-provided.html#priv_show-view">
<code class="literal">
SHOW VIEW
</code>
</a>
privilege
for any explained view.
<a class="link" href="explain.html" title="15.8.2 EXPLAIN Statement">
<code class="literal">
EXPLAIN ... FOR
CONNECTION
</code>
</a>
also requires the
<a class="link" href="privileges-provided.html#priv_process">
<code class="literal">
PROCESS
</code>
</a>
privilege if the
specified connection belongs to a different user.
</p>
<p>
The
<a class="link" href="server-system-variables.html#sysvar_explain_format">
<code class="literal">
explain_format
</code>
</a>
system
variable determines the format of the output from
<code class="literal">
EXPLAIN
</code>
when used to display a query
execution plan. This variable can take any of the values used
with the
<code class="literal">
FORMAT
</code>
option, with the addition of
<code class="literal">
DEFAULT
</code>
as a synonym for
<code class="literal">
TRADITIONAL
</code>
. The following example uses the
<code class="literal">
country
</code>
table from the
<code class="literal">
world
</code>
database which can be obtained from
<a class="ulink" href="/doc/index-other.html" target="_top">
MySQL: Other
Downloads
</a>
:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa11144878"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">USE</span> world<span class="token punctuation">;</span> <span class="token comment" spellcheck="true"># Make world the current database</span>
<span class="token keyword">Database</span> <span class="token keyword">changed</span></code></pre>
</div>
<p>
Checking the value of
<code class="literal">
explain_format
</code>
, we see
that it has the default value, and that
<code class="literal">
EXPLAIN
</code>
(with no
<code class="literal">
FORMAT
</code>
option) therefore uses the traditional tabular output:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa13899415"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token variable">@@explain_format</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> @@explain_format <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> TRADITIONAL <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output">1 row in set (0.00 sec)</span>
<span class="token prompt">mysql></span> <span class="token keyword">EXPLAIN</span> <span class="token keyword">SELECT</span> <span class="token keyword">Name</span> <span class="token keyword">FROM</span> country <span class="token keyword">WHERE</span> <span class="token keyword">Code</span> <span class="token operator">Like</span> <span class="token string">'A%'</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> id <span class="token punctuation">|</span> select_type <span class="token punctuation">|</span> table <span class="token punctuation">|</span> partitions <span class="token punctuation">|</span> type <span class="token punctuation">|</span> possible_keys <span class="token punctuation">|</span> key <span class="token punctuation">|</span> key_len <span class="token punctuation">|</span> ref <span class="token punctuation">|</span> rows <span class="token punctuation">|</span> filtered <span class="token punctuation">|</span> Extra <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> 1 <span class="token punctuation">|</span> SIMPLE <span class="token punctuation">|</span> country <span class="token punctuation">|</span> NULL <span class="token punctuation">|</span> range <span class="token punctuation">|</span> PRIMARY <span class="token punctuation">|</span> PRIMARY <span class="token punctuation">|</span> 12 <span class="token punctuation">|</span> NULL <span class="token punctuation">|</span> 17 <span class="token punctuation">|</span> 100.00 <span class="token punctuation">|</span> Using where <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output">1 row in set, 1 warning (0.00 sec)</span></code></pre>
</div>
<p>
If we set the value of
<code class="literal">
explain_format
</code>
to
<code class="literal">
TREE
</code>
, then rerun the same
<code class="literal">
EXPLAIN
</code>
statement, the output uses the
tree-like format:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa1588670"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SET</span> <span class="token variable">@@explain_format</span><span class="token operator">=</span><span class="token keyword">TREE</span><span class="token punctuation">;</span>
<span class="token output">Query OK, 0 rows affected (0.00 sec)</span>
<span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token variable">@@explain_format</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> @@explain_format <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> TREE <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output">1 row in set (0.00 sec)</span>
<span class="token prompt">mysql></span> <span class="token keyword">EXPLAIN</span> <span class="token keyword">SELECT</span> <span class="token keyword">Name</span> <span class="token keyword">FROM</span> country <span class="token keyword">WHERE</span> <span class="token keyword">Code</span> <span class="token operator">LIKE</span> <span class="token string">'A%'</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> EXPLAIN <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token operator">|</span> <span class="token operator">-</span><span class="token operator">></span> <span class="token keyword">Filter</span>: <span class="token punctuation">(</span>country<span class="token punctuation">.</span><span class="token punctuation">`</span><span class="token keyword">Code</span><span class="token punctuation">`</span> <span class="token operator">like</span> <span class="token string">'A%'</span><span class="token punctuation">)</span> <span class="token punctuation">(</span>cost<span class="token operator">=</span><span class="token number">3.67</span> <span class="token keyword">rows</span><span class="token operator">=</span><span class="token number">17</span><span class="token punctuation">)</span>
<span class="token prompt"> -></span> <span class="token keyword">Index</span> <span class="token keyword">range</span> scan <span class="token keyword">on</span> country <span class="token keyword">using</span> <span class="token keyword">PRIMARY</span> <span class="token keyword">over</span> <span class="token punctuation">(</span><span class="token string">'A'</span> <span class="token operator"><=</span> <span class="token keyword">Code</span> <span class="token operator"><=</span> <span class="token string">'A????????'</span><span class="token punctuation">)</span> <span class="token punctuation">(</span>cost<span class="token operator">=</span><span class="token number">3.67</span> <span class="token keyword">rows</span><span class="token operator">=</span><span class="token number">17</span><span class="token punctuation">)</span> <span class="token operator">|</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output">1 row in set, 1 warning (0.00 sec)</span></code></pre>
</div>
<p>
As stated previously, the
<code class="literal">
FORMAT
</code>
option
overrides this setting. Executing the same
<code class="literal">
EXPLAIN
</code>
statement using
<code class="literal">
FORMAT=JSON
</code>
instead of
<code class="literal">
FORMAT=TREE
</code>
shows that this is the case:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa81963003"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">EXPLAIN</span> <span class="token keyword">FORMAT</span><span class="token operator">=</span><span class="token datatype">JSON</span> <span class="token keyword">SELECT</span> <span class="token keyword">Name</span> <span class="token keyword">FROM</span> country <span class="token keyword">WHERE</span> <span class="token keyword">Code</span> <span class="token operator">LIKE</span> <span class="token string">'A%'</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> EXPLAIN <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token operator">|</span> {
<span class="token string">"query_block"</span>: {
<span class="token string">"select_id"</span>: <span class="token number">1</span><span class="token punctuation">,</span>
<span class="token string">"cost_info"</span>: {
<span class="token string">"query_cost"</span>: <span class="token string">"3.67"</span>
}<span class="token punctuation">,</span>
<span class="token string">"table"</span>: {
<span class="token string">"table_name"</span>: <span class="token string">"country"</span><span class="token punctuation">,</span>
<span class="token string">"access_type"</span>: <span class="token string">"range"</span><span class="token punctuation">,</span>
<span class="token string">"possible_keys"</span>: <span class="token punctuation">[</span>
<span class="token string">"PRIMARY"</span>
<span class="token punctuation">]</span><span class="token punctuation">,</span>
<span class="token string">"key"</span>: <span class="token string">"PRIMARY"</span><span class="token punctuation">,</span>
<span class="token string">"used_key_parts"</span>: <span class="token punctuation">[</span>
<span class="token string">"Code"</span>
<span class="token punctuation">]</span><span class="token punctuation">,</span>
<span class="token string">"key_length"</span>: <span class="token string">"12"</span><span class="token punctuation">,</span>
<span class="token string">"rows_examined_per_scan"</span>: <span class="token number">17</span><span class="token punctuation">,</span>
<span class="token string">"rows_produced_per_join"</span>: <span class="token number">17</span><span class="token punctuation">,</span>
<span class="token string">"filtered"</span>: <span class="token string">"100.00"</span><span class="token punctuation">,</span>
<span class="token string">"cost_info"</span>: {
<span class="token string">"read_cost"</span>: <span class="token string">"1.97"</span><span class="token punctuation">,</span>
<span class="token string">"eval_cost"</span>: <span class="token string">"1.70"</span><span class="token punctuation">,</span>
<span class="token string">"prefix_cost"</span>: <span class="token string">"3.67"</span><span class="token punctuation">,</span>
<span class="token string">"data_read_per_join"</span>: <span class="token string">"16K"</span>
}<span class="token punctuation">,</span>
<span class="token string">"used_columns"</span>: <span class="token punctuation">[</span>
<span class="token string">"Code"</span><span class="token punctuation">,</span>
<span class="token string">"Name"</span>
<span class="token punctuation">]</span><span class="token punctuation">,</span>
<span class="token string">"attached_condition"</span>: <span class="token string">"(`world`.`country`.`Code` like 'A%')"</span>
}
}
} <span class="token operator">|</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output">1 row in set, 1 warning (0.00 sec)</span></code></pre>
</div>
<p>
To return the default output of
<code class="literal">
EXPLAIN
</code>
to
the tabular format, set
<code class="literal">
explain_format
</code>
to
<code class="literal">
TRADITIONAL
</code>
. Alternatively, you can set it to
<code class="literal">
DEFAULT
</code>
, which has the same effect, as shown
here:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa5299114"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SET</span> <span class="token variable">@@explain_format</span><span class="token operator">=</span><span class="token keyword">DEFAULT</span><span class="token punctuation">;</span>
<span class="token output">Query OK, 0 rows affected (0.00 sec)</span>
<span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token variable">@@explain_format</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> @@explain_format <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> TRADITIONAL <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output">1 row in set (0.00 sec)</span></code></pre>
</div>
<a class="indexterm" name="idm46045168008576">
</a>
<a class="indexterm" name="idm46045168007072">
</a>
<p>
MySQL 8.4 supports two versions of the JSON output
format. Version 1 is the linear format always used in MySQL 8.2
and earlier; this remains the default in MySQL 8.4,
and is used in the examples already shown in this section.
Version 2 of the JSON output format is based on access paths,
and is intended to provide compatibility with future versions of
the MySQL Optimizer. You can switch to the Version 2 format by
setting the value of the
<a class="link" href="server-system-variables.html#sysvar_explain_json_format_version">
<code class="literal">
explain_json_format_version
</code>
</a>
server system variable to
<code class="literal">
2
</code>
, as shown here
for the same
<code class="literal">
EXPLAIN
</code>
statement used in the
previous example:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa19629347"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token variable">@@explain_json_format_version</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> @@explain_json_format_version <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> 1 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output">1 row in set (0.00 sec)</span>
<span class="token prompt">mysql></span> <span class="token keyword">SET</span> <span class="token variable">@@explain_json_format_version</span> <span class="token operator">=</span> <span class="token number">2</span><span class="token punctuation">;</span>
<span class="token output">Query OK, 0 rows affected (0.00 sec)</span>
<span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token variable">@@explain_json_format_version</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> @@explain_json_format_version <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> 2 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output">1 row in set (0.00 sec)</span>
<span class="token prompt">mysql></span> <span class="token keyword">EXPLAIN</span> <span class="token keyword">FORMAT</span><span class="token operator">=</span><span class="token datatype">JSON</span> <span class="token keyword">SELECT</span> <span class="token keyword">Name</span> <span class="token keyword">FROM</span> country <span class="token keyword">WHERE</span> <span class="token keyword">Code</span> <span class="token operator">LIKE</span> <span class="token string">'A%'</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> EXPLAIN <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token operator">|</span> {
<span class="token string">"query"</span>: <span class="token string">"/* select#1 */ select `world`.`country`.`Name` AS `Name` from `world`.`country` where (`world`.`country`.`Code` like 'A%')"</span><span class="token punctuation">,</span>
<span class="token string">"inputs"</span>: <span class="token punctuation">[</span>
<span class="token inlinejson"> <span class="token punctuation">{</span>
<span class="token property">"ranges"</span><span class="token operator">:</span> <span class="token punctuation">[</span>
<span class="token string">"('A' <= Code <= 'A????????')"</span>
<span class="token punctuation">]</span><span class="token punctuation">,</span>
<span class="token property">"covering"</span><span class="token operator">:</span> <span class="token boolean">false</span><span class="token punctuation">,</span>
<span class="token property">"operation"</span><span class="token operator">:</span> <span class="token string">"Index range scan on country using PRIMARY over ('A' <= Code < 'A????????')"</span><span class="token punctuation">,</span>
<span class="token property">"index_name"</span><span class="token operator">:</span> <span class="token string">"PRIMARY"</span><span class="token punctuation">,</span>
<span class="token property">"table_name"</span><span class="token operator">:</span> <span class="token string">"country"</span><span class="token punctuation">,</span>
<span class="token property">"access_type"</span><span class="token operator">:</span> <span class="token string">"index"</span><span class="token punctuation">,</span>
<span class="token property">"estimated_rows"</span><span class="token operator">:</span> <span class="token number">17.0</span><span class="token punctuation">,</span>
<span class="token property">"index_access_type"</span><span class="token operator">:</span> <span class="token string">"index_range_scan"</span><span class="token punctuation">,</span>
<span class="token property">"estimated_total_cost"</span><span class="token operator">:</span> <span class="token number">3.668778400708174</span>
<span class="token punctuation">}</span></span>
<span class="token punctuation">]</span><span class="token punctuation">,</span>
<span class="token string">"condition"</span>: <span class="token string">"(country.`Code` like 'A%')"</span><span class="token punctuation">,</span>
<span class="token string">"operation"</span>: <span class="token string">"Filter: (country.`Code` like 'A%')"</span><span class="token punctuation">,</span>
<span class="token string">"access_type"</span>: <span class="token string">"filter"</span><span class="token punctuation">,</span>
<span class="token string">"estimated_rows"</span>: <span class="token number">17.0</span><span class="token punctuation">,</span>
<span class="token string">"estimated_total_cost"</span>: <span class="token number">3.668778400708174</span>
} <span class="token operator">|</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span></code></pre>
</div>
<p>
After using the Version 2 format, you can cause the JSON output
from all subsequent
<code class="literal">
EXPLAIN FORMAT=JSON
</code>
statements to revert to the Version 1 format by setting
<code class="literal">
explain_json_format_version
</code>
back to
<code class="literal">
1
</code>
(the default).
</p>
<p>
The value of
<code class="literal">
explain_json_format_version
</code>
determines the version of the JSON output format employed by all
<code class="literal">
EXPLAIN
</code>
statements which use it, whether the
JSON format is used because a given
<code class="literal">
EXPLAIN
</code>
statement includes an explicit
<code class="literal">
FORMAT=JSON
</code>
option, or because the JSON format is used automatically due to
the
<a class="link" href="server-system-variables.html#sysvar_explain_format">
<code class="literal">
explain_format
</code>
</a>
system
variable being set to
<code class="literal">
JSON
</code>
.
</p>
<a class="indexterm" name="idm46045167985984">
</a>
<p>
With the help of
<a class="link" href="explain.html" title="15.8.2 EXPLAIN Statement">
<code class="literal">
EXPLAIN
</code>
</a>
, you can
see where you should add indexes to tables so that the statement
executes faster by using indexes to find rows. You can also use
<a class="link" href="explain.html" title="15.8.2 EXPLAIN Statement">
<code class="literal">
EXPLAIN
</code>
</a>
to check whether the
optimizer joins the tables in an optimal order. To give a hint
to the optimizer to use a join order corresponding to the order
in which the tables are named in a
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT
</code>
</a>
statement, begin the
statement with
<code class="literal">
SELECT STRAIGHT_JOIN
</code>
rather
than just
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT
</code>
</a>
. (See
<a class="xref" href="select.html" title="15.2.13 SELECT Statement">
Section 15.2.13, “SELECT Statement”
</a>
.)
</p>
<p>
The optimizer trace may sometimes provide information
complementary to that of
<a class="link" href="explain.html" title="15.8.2 EXPLAIN Statement">
<code class="literal">
EXPLAIN
</code>
</a>
.
However, the optimizer trace format and content are subject to
change between versions. For details, see
<a class="xref" href="optimizer-tracing.html" title="10.15 Tracing the Optimizer">
Section 10.15, “Tracing the Optimizer”
</a>
.
</p>
<p>
If you have a problem with indexes not being used when you
believe that they should be, run
<a class="link" href="analyze-table.html" title="15.7.3.1 ANALYZE TABLE Statement">
<code class="literal">
ANALYZE
TABLE
</code>
</a>
to update table statistics, such as cardinality
of keys, that can affect the choices the optimizer makes. See
<a class="xref" href="analyze-table.html" title="15.7.3.1 ANALYZE TABLE Statement">
Section 15.7.3.1, “ANALYZE TABLE Statement”
</a>
.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
MySQL Workbench has a Visual Explain capability that provides a
visual representation of
<a class="link" href="explain.html" title="15.8.2 EXPLAIN Statement">
<code class="literal">
EXPLAIN
</code>
</a>
output. See
<a class="ulink" href="/doc/workbench/en/wb-tutorial-visual-explain-dbt3.html" target="_top">
Tutorial: Using Explain to Improve Query Performance
</a>
.
</p>
</div>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h4 class="title">
<a name="explain-analyze">
</a>
Obtaining Information with EXPLAIN ANALYZE
</h4>
</div>
</div>
</div>
<p>
<code class="literal">
EXPLAIN ANALYZE
</code>
runs a statement and produces
<a class="link" href="explain.html#explain-execution-plan" title="Obtaining Execution Plan Information">
<code class="literal">
EXPLAIN
</code>
</a>
output along with timing and additional, iterator-based,
information about how the optimizer's expectations matched
the actual execution. For each iterator, the following
information is provided:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
Estimated execution cost
</p>
<p>
(Some iterators are not accounted for by the cost model, and
so are not included in the estimate.)
</p>
</li>
<li class="listitem">
<p>
Estimated number of returned rows
</p>
</li>
<li class="listitem">
<p>
Time to return first row
</p>
</li>
<li class="listitem">
<p>
Time spent executing this iterator (including child
iterators, but not parent iterators), in milliseconds.
</p>
<p>
(When there are multiple loops, this figure shows the
average time per loop.)
</p>
</li>
<li class="listitem">
<p>
Number of rows returned by the iterator
</p>
</li>
<li class="listitem">
<p>
Number of loops
</p>
</li>
</ul>
</div>
<p>
The query execution information is displayed using the
<code class="literal">
TREE
</code>
output format, in which nodes represent
iterators.
<code class="literal">
EXPLAIN ANALYZE
</code>
always uses the
<code class="literal">
TREE
</code>
output format. This can optionally be
specified explicitly using
<code class="literal">
FORMAT=TREE
</code>
;
formats other than
<code class="literal">
TREE
</code>
remain unsupported.
</p>
<p>
<code class="literal">
EXPLAIN ANALYZE
</code>
can be used with
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT
</code>
</a>
statements, multi-table
<a class="link" href="update.html" title="15.2.17 UPDATE Statement">
<code class="literal">
UPDATE
</code>
</a>
and
<a class="link" href="delete.html" title="15.2.2 DELETE Statement">
<code class="literal">
DELETE
</code>
</a>
statements, and
<a class="link" href="table.html" title="15.2.16 TABLE Statement">
<code class="literal">
TABLE
</code>
</a>
statements.
</p>
<p>
You can terminate this statement using
<a class="link" href="kill.html" title="15.7.8.4 KILL Statement">
<code class="literal">
KILL QUERY
</code>
</a>
or
<span class="keycap">
<strong>
CTRL-C
</strong>
</span>
.
</p>
<p>
<code class="literal">
EXPLAIN ANALYZE
</code>
cannot be used with
<code class="literal">
FOR CONNECTION
</code>
.
</p>
<p>
Example output:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa77680242"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">EXPLAIN</span> <span class="token keyword">ANALYZE</span> <span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> t1 <span class="token keyword">JOIN</span> t2 <span class="token keyword">ON</span> <span class="token punctuation">(</span>t1<span class="token punctuation">.</span>c1 <span class="token operator">=</span> t2<span class="token punctuation">.</span>c2<span class="token punctuation">)</span>\G
<span class="token output"><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span> 1. row <span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span>
EXPLAIN<span class="token punctuation">:</span> -> Inner hash join (t2.c2 = t1.c1) (cost=3.5 rows=5)
(actual time=0.121..0.131 rows=1 loops=1) </span>
<span class="token prompt"> -></span> <span class="token keyword">Table</span> scan <span class="token keyword">on</span> t2 <span class="token punctuation">(</span>cost<span class="token operator">=</span><span class="token number">0.07</span> <span class="token keyword">rows</span><span class="token operator">=</span><span class="token number">5</span><span class="token punctuation">)</span>
<span class="token punctuation">(</span>actual <span class="token datatype">time</span><span class="token operator">=</span><span class="token number">0.0126</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token number">0.0221</span> <span class="token keyword">rows</span><span class="token operator">=</span><span class="token number">5</span> loops<span class="token operator">=</span><span class="token number">1</span><span class="token punctuation">)</span>
<span class="token prompt"> -></span> <span class="token keyword">Hash</span>
<span class="token prompt"> -></span> <span class="token keyword">Table</span> scan <span class="token keyword">on</span> t1 <span class="token punctuation">(</span>cost<span class="token operator">=</span><span class="token number">0.75</span> <span class="token keyword">rows</span><span class="token operator">=</span><span class="token number">5</span><span class="token punctuation">)</span>
<span class="token punctuation">(</span>actual <span class="token datatype">time</span><span class="token operator">=</span><span class="token number">0.0372</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token number">0.0534</span> <span class="token keyword">rows</span><span class="token operator">=</span><span class="token number">5</span> loops<span class="token operator">=</span><span class="token number">1</span><span class="token punctuation">)</span>
<span class="token prompt">mysql></span> <span class="token keyword">EXPLAIN</span> <span class="token keyword">ANALYZE</span> <span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> t3 <span class="token keyword">WHERE</span> i <span class="token operator">></span> <span class="token number">8</span>\G
<span class="token output"><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span> 1. row <span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span>
EXPLAIN<span class="token punctuation">:</span> -> Filter<span class="token punctuation">:</span> (t3.i > 8) (cost=0.75 rows=1.67)
(actual time=0.0168..0.0182 rows=1 loops=1)</span>
<span class="token prompt"> -></span> <span class="token keyword">Table</span> scan <span class="token keyword">on</span> t3 <span class="token punctuation">(</span>cost<span class="token operator">=</span><span class="token number">0.75</span> <span class="token keyword">rows</span><span class="token operator">=</span><span class="token number">5</span><span class="token punctuation">)</span>
<span class="token punctuation">(</span>actual <span class="token datatype">time</span><span class="token operator">=</span><span class="token number">0.015</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token number">0.0167</span> <span class="token keyword">rows</span><span class="token operator">=</span><span class="token number">5</span> loops<span class="token operator">=</span><span class="token number">1</span><span class="token punctuation">)</span>
<span class="token prompt">mysql></span> <span class="token keyword">EXPLAIN</span> <span class="token keyword">ANALYZE</span> <span class="token keyword">FORMAT</span><span class="token operator">=</span><span class="token keyword">TREE</span> <span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> t3 <span class="token keyword">WHERE</span> pk <span class="token operator">></span> <span class="token number">17</span>\G
<span class="token output"><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span> 1. row <span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span>
EXPLAIN<span class="token punctuation">:</span> -> Filter<span class="token punctuation">:</span> (t3.pk > 17) (cost=0.91 rows=2)
(actual time=0.0334..0.042 rows=2 loops=1)</span>
<span class="token prompt"> -></span> <span class="token keyword">Index</span> <span class="token keyword">range</span> scan <span class="token keyword">on</span> t3 <span class="token keyword">using</span> <span class="token keyword">PRIMARY</span> <span class="token keyword">over</span> <span class="token punctuation">(</span><span class="token number">17</span> <span class="token operator"><</span> pk<span class="token punctuation">)</span>
<span class="token punctuation">(</span>cost<span class="token operator">=</span><span class="token number">0.91</span> <span class="token keyword">rows</span><span class="token operator">=</span><span class="token number">2</span><span class="token punctuation">)</span> <span class="token punctuation">(</span>actual <span class="token datatype">time</span><span class="token operator">=</span><span class="token number">0.0306</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token number">0.0384</span> <span class="token keyword">rows</span><span class="token operator">=</span><span class="token number">2</span> loops<span class="token operator">=</span><span class="token number">1</span><span class="token punctuation">)</span></code></pre>
</div>
<p>
The tables used in the example output were created by the
statements shown here:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa31774541"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> t1 <span class="token punctuation">(</span>
c1 <span class="token datatype">INTEGER</span> <span class="token keyword">DEFAULT</span> <span class="token boolean">NULL</span><span class="token punctuation">,</span>
c2 <span class="token datatype">INTEGER</span> <span class="token keyword">DEFAULT</span> <span class="token boolean">NULL</span>
<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> t2 <span class="token punctuation">(</span>
c1 <span class="token datatype">INTEGER</span> <span class="token keyword">DEFAULT</span> <span class="token boolean">NULL</span><span class="token punctuation">,</span>
c2 <span class="token datatype">INTEGER</span> <span class="token keyword">DEFAULT</span> <span class="token boolean">NULL</span>
<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> t3 <span class="token punctuation">(</span>
pk <span class="token datatype">INTEGER</span> <span class="token operator">NOT</span> <span class="token boolean">NULL</span> <span class="token keyword">PRIMARY</span> <span class="token keyword">KEY</span><span class="token punctuation">,</span>
i <span class="token datatype">INTEGER</span> <span class="token keyword">DEFAULT</span> <span class="token boolean">NULL</span>
<span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
Values shown for
<code class="literal">
actual time
</code>
in the output of
this statement are expressed in milliseconds.
</p>
<p>
<a class="link" href="server-system-variables.html#sysvar_explain_format">
<code class="literal">
explain_format
</code>
</a>
has the
following effects on
<code class="literal">
EXPLAIN ANALYZE
</code>
:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
If the value of this variable is
<code class="literal">
TRADITIONAL
</code>
or
<code class="literal">
TREE
</code>
(or the synonym
<code class="literal">
DEFAULT
</code>
),
<code class="literal">
EXPLAIN ANALYZE
</code>
uses the
<code class="literal">
TREE
</code>
format. This ensures that this
statement continues to use the
<code class="literal">
TREE
</code>
format by default, as it did prior to the introduction of
<code class="literal">
explain_format
</code>
.
</p>
</li>
<li class="listitem">
<p>
If the value of
<code class="literal">
explain_format
</code>
is
<code class="literal">
JSON
</code>
,
<code class="literal">
EXPLAIN ANALYZE
</code>
returns an error unless
<code class="literal">
FORMAT=TREE
</code>
is
specified as part of the statement. This is due to the fact
that
<code class="literal">
EXPLAIN ANALYZE
</code>
supports only the
<code class="literal">
TREE
</code>
output format.
</p>
</li>
</ul>
</div>
<p>
We illustrate the behavior described in the second point here,
re-using the last
<code class="literal">
EXPLAIN ANALYZE
</code>
statement
from the previous example:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa67455450"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SET</span> <span class="token variable">@@explain_format</span><span class="token operator">=</span><span class="token datatype">JSON</span><span class="token punctuation">;</span>
<span class="token output">Query OK, 0 rows affected (0.00 sec)</span>
<span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token variable">@@explain_format</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> @@explain_format <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> JSON <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output">1 row in set (0.00 sec)</span>
<span class="token prompt">mysql></span> <span class="token keyword">EXPLAIN</span> <span class="token keyword">ANALYZE</span> <span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> t3 <span class="token keyword">WHERE</span> pk <span class="token operator">></span> <span class="token number">17</span>\G
<span class="token output">ERROR 1235 (42000)<span class="token punctuation">:</span> This version of MySQL doesn't yet support 'EXPLAIN ANALYZE with JSON format'
</span>
<span class="token prompt">mysql></span> <span class="token keyword">EXPLAIN</span> <span class="token keyword">ANALYZE</span> <span class="token keyword">FORMAT</span><span class="token operator">=</span><span class="token keyword">TRADITIONAL</span> <span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> t3 <span class="token keyword">WHERE</span> pk <span class="token operator">></span> <span class="token number">17</span>\G
<span class="token output">ERROR 1235 (42000)<span class="token punctuation">:</span> This version of MySQL doesn't yet support 'EXPLAIN ANALYZE with TRADITIONAL format'
</span>
<span class="token prompt">mysql></span> <span class="token keyword">EXPLAIN</span> <span class="token keyword">ANALYZE</span> <span class="token keyword">FORMAT</span><span class="token operator">=</span><span class="token keyword">TREE</span> <span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> t3 <span class="token keyword">WHERE</span> pk <span class="token operator">></span> <span class="token number">17</span>\G
<span class="token output"><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span> 1. row <span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span>
EXPLAIN<span class="token punctuation">:</span> -> Filter<span class="token punctuation">:</span> (t3.pk > 17) (cost=1.26 rows=5)
(actual time=0.013..0.016 rows=5 loops=1)</span>
<span class="token prompt"> -></span> <span class="token keyword">Index</span> <span class="token keyword">range</span> scan <span class="token keyword">on</span> t3 <span class="token keyword">using</span> <span class="token keyword">PRIMARY</span> <span class="token punctuation">(</span>cost<span class="token operator">=</span><span class="token number">1.26</span> <span class="token keyword">rows</span><span class="token operator">=</span><span class="token number">5</span><span class="token punctuation">)</span>
<span class="token punctuation">(</span>actual <span class="token datatype">time</span><span class="token operator">=</span><span class="token number">0.012</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token number">0.014</span> <span class="token keyword">rows</span><span class="token operator">=</span><span class="token number">5</span> loops<span class="token operator">=</span><span class="token number">1</span><span class="token punctuation">)</span></code></pre>
</div>
<p>
Using
<code class="literal">
FORMAT=TRADITIONAL
</code>
or
<code class="literal">
FORMAT=JSON
</code>
with
<code class="literal">
EXPLAIN
ANALYZE
</code>
always raises an error, regardless of the
value of
<code class="literal">
explain_format
</code>
.
</p>
<p>
In MySQL 8.4, numbers in the output of
<code class="literal">
EXPLAIN ANALYZE
</code>
and
<code class="literal">
EXPLAIN
FORMAT=TREE
</code>
are formatted according to the following
rules:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
Numbers in the range 0.001-999999.5 are printed as decimal
numbers.
</p>
<p>
Decimal numbers less than 1000 have three significant
digits; the remainder have four, five, or six.
</p>
</li>
<li class="listitem">
<p>
Numbers outside the range 0.001-999999.5 are printed in
engineering format. Examples of such values are
<code class="literal">
1.23e+9
</code>
and
<code class="literal">
934e-6
</code>
.
</p>
</li>
<li class="listitem">
<p>
No trailing zeros are printed. For example, we print
<code class="literal">
2.3
</code>
rather than
<code class="literal">
2.30
</code>
,
and
<code class="literal">
1.2e+6
</code>
rather than
<code class="literal">
1.20e+6
</code>
.
</p>
</li>
<li class="listitem">
<p>
Numbers less than
<code class="literal">
1e-12
</code>
are printed as
<code class="literal">
0
</code>
.
</p>
</li>
</ul>
</div>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/innodb-locks-set.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="innodb-locks-set">
</a>
17.7.3 Locks Set by Different SQL Statements in InnoDB
</h3>
</div>
</div>
</div>
<a class="indexterm" name="idm46045164036128">
</a>
<a class="indexterm" name="idm46045164035088">
</a>
<p>
A
<a class="link" href="glossary.html#glos_locking_read" title="locking read">
locking read
</a>
, an
<a class="link" href="update.html" title="15.2.17 UPDATE Statement">
<code class="literal">
UPDATE
</code>
</a>
, or a
<a class="link" href="delete.html" title="15.2.2 DELETE Statement">
<code class="literal">
DELETE
</code>
</a>
generally set record locks
on every index record that is scanned in the processing of an SQL
statement. It does not matter whether there are
<code class="literal">
WHERE
</code>
conditions in the statement that would
exclude the row.
<code class="literal">
InnoDB
</code>
does not remember the
exact
<code class="literal">
WHERE
</code>
condition, but only knows which
index ranges were scanned. The locks are normally
<a class="link" href="glossary.html#glos_next_key_lock" title="next-key lock">
next-key locks
</a>
that also
block inserts into the
<span class="quote">
“
<span class="quote">
gap
</span>
”
</span>
immediately before the
record. However,
<a class="link" href="glossary.html#glos_gap_lock" title="gap lock">
gap locking
</a>
can be disabled explicitly, which causes next-key locking not to
be used. For more information, see
<a class="xref" href="innodb-locking.html" title="17.7.1 InnoDB Locking">
Section 17.7.1, “InnoDB Locking”
</a>
. The transaction isolation level
can also affect which locks are set; see
<a class="xref" href="innodb-transaction-isolation-levels.html" title="17.7.2.1 Transaction Isolation Levels">
Section 17.7.2.1, “Transaction Isolation Levels”
</a>
.
</p>
<p>
If a secondary index is used in a search and the index record
locks to be set are exclusive,
<code class="literal">
InnoDB
</code>
also
retrieves the corresponding clustered index records and sets locks
on them.
</p>
<p>
If you have no indexes suitable for your statement and MySQL must
scan the entire table to process the statement, every row of the
table becomes locked, which in turn blocks all inserts by other
users to the table. It is important to create good indexes so that
your queries do not scan more rows than necessary.
</p>
<p>
<code class="literal">
InnoDB
</code>
sets specific types of locks as follows.
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT ...
FROM
</code>
</a>
is a consistent read, reading a snapshot of the
database and setting no locks unless the transaction isolation
level is set to
<a class="link" href="innodb-transaction-isolation-levels.html#isolevel_serializable">
<code class="literal">
SERIALIZABLE
</code>
</a>
. For
<a class="link" href="innodb-transaction-isolation-levels.html#isolevel_serializable">
<code class="literal">
SERIALIZABLE
</code>
</a>
level, the
search sets shared next-key locks on the index records it
encounters. However, only an index record lock is required for
statements that lock rows using a unique index to search for a
unique row.
</p>
</li>
<li class="listitem">
<p>
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT ... FOR
UPDATE
</code>
</a>
and
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT ... FOR
SHARE
</code>
</a>
statements that use a unique index acquire
locks for scanned rows, and release the locks for rows that do
not qualify for inclusion in the result set (for example, if
they do not meet the criteria given in the
<code class="literal">
WHERE
</code>
clause). However, in some cases, rows
might not be unlocked immediately because the relationship
between a result row and its original source is lost during
query execution. For example, in a
<a class="link" href="union.html" title="15.2.18 UNION Clause">
<code class="literal">
UNION
</code>
</a>
, scanned (and locked)
rows from a table might be inserted into a temporary table
before evaluating whether they qualify for the result set. In
this circumstance, the relationship of the rows in the
temporary table to the rows in the original table is lost and
the latter rows are not unlocked until the end of query
execution.
</p>
</li>
<li class="listitem">
<p>
For
<a class="link" href="glossary.html#glos_locking_read" title="locking read">
locking reads
</a>
(
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT
</code>
</a>
with
<code class="literal">
FOR
UPDATE
</code>
or
<code class="literal">
FOR SHARE
</code>
),
<a class="link" href="update.html" title="15.2.17 UPDATE Statement">
<code class="literal">
UPDATE
</code>
</a>
, and
<a class="link" href="delete.html" title="15.2.2 DELETE Statement">
<code class="literal">
DELETE
</code>
</a>
statements, the locks
that are taken depend on whether the statement uses a unique
index with a unique search condition or a range-type search
condition.
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<p>
For a unique index with a unique search condition,
<code class="literal">
InnoDB
</code>
locks only the index record
found, not the
<a class="link" href="glossary.html#glos_gap" title="gap">
gap
</a>
before
it.
</p>
</li>
<li class="listitem">
<p>
For other search conditions, and for non-unique indexes,
<code class="literal">
InnoDB
</code>
locks the index range scanned,
using
<a class="link" href="glossary.html#glos_gap_lock" title="gap lock">
gap locks
</a>
or
<a class="link" href="glossary.html#glos_next_key_lock" title="next-key lock">
next-key locks
</a>
to block insertions by other sessions into the gaps
covered by the range. For information about gap locks and
next-key locks, see
<a class="xref" href="innodb-locking.html" title="17.7.1 InnoDB Locking">
Section 17.7.1, “InnoDB Locking”
</a>
.
</p>
</li>
</ul>
</div>
</li>
<li class="listitem">
<p>
For index records the search encounters,
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT ... FOR
UPDATE
</code>
</a>
blocks other sessions from doing
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT ... FOR
SHARE
</code>
</a>
or from reading in certain transaction
isolation levels. Consistent reads ignore any locks set on the
records that exist in the read view.
</p>
</li>
<li class="listitem">
<p>
<a class="link" href="update.html" title="15.2.17 UPDATE Statement">
<code class="literal">
UPDATE ... WHERE
...
</code>
</a>
sets an exclusive next-key lock on every record
the search encounters. However, only an index record lock is
required for statements that lock rows using a unique index to
search for a unique row.
</p>
</li>
<li class="listitem">
<p>
When
<a class="link" href="update.html" title="15.2.17 UPDATE Statement">
<code class="literal">
UPDATE
</code>
</a>
modifies a
clustered index record, implicit locks are taken on affected
secondary index records. The
<a class="link" href="update.html" title="15.2.17 UPDATE Statement">
<code class="literal">
UPDATE
</code>
</a>
operation also takes
shared locks on affected secondary index records when
performing duplicate check scans prior to inserting new
secondary index records, and when inserting new secondary
index records.
</p>
</li>
<li class="listitem">
<p>
<a class="link" href="delete.html" title="15.2.2 DELETE Statement">
<code class="literal">
DELETE FROM ... WHERE
...
</code>
</a>
sets an exclusive next-key lock on every record
the search encounters. However, only an index record lock is
required for statements that lock rows using a unique index to
search for a unique row.
</p>
</li>
<li class="listitem">
<p>
<a class="link" href="insert.html" title="15.2.7 INSERT Statement">
<code class="literal">
INSERT
</code>
</a>
sets an exclusive lock
on the inserted row. This lock is an index-record lock, not a
next-key lock (that is, there is no gap lock) and does not
prevent other sessions from inserting into the gap before the
inserted row.
</p>
<p>
Prior to inserting the row, a type of gap lock called an
insert intention gap lock is set. This lock signals the intent
to insert in such a way that multiple transactions inserting
into the same index gap need not wait for each other if they
are not inserting at the same position within the gap. Suppose
that there are index records with values of 4 and 7. Separate
transactions that attempt to insert values of 5 and 6 each
lock the gap between 4 and 7 with insert intention locks prior
to obtaining the exclusive lock on the inserted row, but do
not block each other because the rows are nonconflicting.
</p>
<p>
If a duplicate-key error occurs, a shared lock on the
duplicate index record is set. This use of a shared lock can
result in deadlock should there be multiple sessions trying to
insert the same row if another session already has an
exclusive lock. This can occur if another session deletes the
row. Suppose that an
<code class="literal">
InnoDB
</code>
table
<code class="literal">
t1
</code>
has the following structure:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa7694736"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> t1 <span class="token punctuation">(</span>i <span class="token datatype">INT</span><span class="token punctuation">,</span> <span class="token keyword">PRIMARY</span> <span class="token keyword">KEY</span> <span class="token punctuation">(</span>i<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token keyword">ENGINE</span> <span class="token operator">=</span> InnoDB<span class="token punctuation">;</span></code></pre>
</div>
<p>
Now suppose that three sessions perform the following
operations in order:
</p>
<p>
Session 1:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa45771180"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">START</span> <span class="token keyword">TRANSACTION</span><span class="token punctuation">;</span>
<span class="token keyword">INSERT</span> <span class="token keyword">INTO</span> t1 <span class="token keyword">VALUES</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
Session 2:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa52191686"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">START</span> <span class="token keyword">TRANSACTION</span><span class="token punctuation">;</span>
<span class="token keyword">INSERT</span> <span class="token keyword">INTO</span> t1 <span class="token keyword">VALUES</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
Session 3:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa10270023"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">START</span> <span class="token keyword">TRANSACTION</span><span class="token punctuation">;</span>
<span class="token keyword">INSERT</span> <span class="token keyword">INTO</span> t1 <span class="token keyword">VALUES</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
Session 1:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa4594321"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">ROLLBACK</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
The first operation by session 1 acquires an exclusive lock
for the row. The operations by sessions 2 and 3 both result in
a duplicate-key error and they both request a shared lock for
the row. When session 1 rolls back, it releases its exclusive
lock on the row and the queued shared lock requests for
sessions 2 and 3 are granted. At this point, sessions 2 and 3
deadlock: Neither can acquire an exclusive lock for the row
because of the shared lock held by the other.
</p>
<p>
A similar situation occurs if the table already contains a row
with key value 1 and three sessions perform the following
operations in order:
</p>
<p>
Session 1:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa6447185"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">START</span> <span class="token keyword">TRANSACTION</span><span class="token punctuation">;</span>
<span class="token keyword">DELETE</span> <span class="token keyword">FROM</span> t1 <span class="token keyword">WHERE</span> i <span class="token operator">=</span> <span class="token number">1</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
Session 2:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa46032661"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">START</span> <span class="token keyword">TRANSACTION</span><span class="token punctuation">;</span>
<span class="token keyword">INSERT</span> <span class="token keyword">INTO</span> t1 <span class="token keyword">VALUES</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
Session 3:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa18725816"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">START</span> <span class="token keyword">TRANSACTION</span><span class="token punctuation">;</span>
<span class="token keyword">INSERT</span> <span class="token keyword">INTO</span> t1 <span class="token keyword">VALUES</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
Session 1:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa75379725"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">COMMIT</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
The first operation by session 1 acquires an exclusive lock
for the row. The operations by sessions 2 and 3 both result in
a duplicate-key error and they both request a shared lock for
the row. When session 1 commits, it releases its exclusive
lock on the row and the queued shared lock requests for
sessions 2 and 3 are granted. At this point, sessions 2 and 3
deadlock: Neither can acquire an exclusive lock for the row
because of the shared lock held by the other.
</p>
</li>
<li class="listitem">
<p>
<a class="link" href="insert-on-duplicate.html" title="15.2.7.2 INSERT ... ON DUPLICATE KEY UPDATE Statement">
<code class="literal">
INSERT
... ON DUPLICATE KEY UPDATE
</code>
</a>
differs from a simple
<a class="link" href="insert.html" title="15.2.7 INSERT Statement">
<code class="literal">
INSERT
</code>
</a>
in that an exclusive
lock rather than a shared lock is placed on the row to be
updated when a duplicate-key error occurs. An exclusive
index-record lock is taken for a duplicate primary key value.
An exclusive next-key lock is taken for a duplicate unique key
value.
</p>
</li>
<li class="listitem">
<p>
<a class="link" href="replace.html" title="15.2.12 REPLACE Statement">
<code class="literal">
REPLACE
</code>
</a>
is done like an
<a class="link" href="insert.html" title="15.2.7 INSERT Statement">
<code class="literal">
INSERT
</code>
</a>
if there is no collision
on a unique key. Otherwise, an exclusive next-key lock is
placed on the row to be replaced.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
INSERT INTO T SELECT ... FROM S WHERE ...
</code>
sets an exclusive index record lock (without a gap lock) on
each row inserted into
<code class="literal">
T
</code>
. If the
transaction isolation level is
<a class="link" href="innodb-transaction-isolation-levels.html#isolevel_read-committed">
<code class="literal">
READ
COMMITTED
</code>
</a>
,
<code class="literal">
InnoDB
</code>
does the search
on
<code class="literal">
S
</code>
as a consistent read (no locks).
Otherwise,
<code class="literal">
InnoDB
</code>
sets shared next-key
locks on rows from
<code class="literal">
S
</code>
.
<code class="literal">
InnoDB
</code>
has to set locks in the latter case:
During roll-forward recovery using a statement-based binary
log, every SQL statement must be executed in exactly the same
way it was done originally.
</p>
<p>
<a class="link" href="create-table.html" title="15.1.20 CREATE TABLE Statement">
<code class="literal">
CREATE TABLE ...
SELECT ...
</code>
</a>
performs the
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT
</code>
</a>
with shared next-key
locks or as a consistent read, as for
<a class="link" href="insert-select.html" title="15.2.7.1 INSERT ... SELECT Statement">
<code class="literal">
INSERT ...
SELECT
</code>
</a>
.
</p>
<p>
When a
<code class="literal">
SELECT
</code>
is used in the constructs
<code class="literal">
REPLACE INTO t SELECT ... FROM s WHERE ...
</code>
or
<code class="literal">
UPDATE t ... WHERE col IN (SELECT ... FROM s
...)
</code>
,
<code class="literal">
InnoDB
</code>
sets shared next-key
locks on rows from table
<code class="literal">
s
</code>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
InnoDB
</code>
sets an exclusive lock on the end of
the index associated with the
<code class="literal">
AUTO_INCREMENT
</code>
column while initializing a
previously specified
<code class="literal">
AUTO_INCREMENT
</code>
column
on a table.
</p>
<p>
With
<a class="link" href="innodb-parameters.html#sysvar_innodb_autoinc_lock_mode">
<code class="literal">
innodb_autoinc_lock_mode=0
</code>
</a>
,
<code class="literal">
InnoDB
</code>
uses a special
<code class="literal">
AUTO-INC
</code>
table lock mode where the lock is
obtained and held to the end of the current SQL statement (not
to the end of the entire transaction) while accessing the
auto-increment counter. Other clients cannot insert into the
table while the
<code class="literal">
AUTO-INC
</code>
table lock is
held. The same behavior occurs for
<span class="quote">
“
<span class="quote">
bulk inserts
</span>
”
</span>
with
<a class="link" href="innodb-parameters.html#sysvar_innodb_autoinc_lock_mode">
<code class="literal">
innodb_autoinc_lock_mode=1
</code>
</a>
.
Table-level
<code class="literal">
AUTO-INC
</code>
locks are not used
with
<a class="link" href="innodb-parameters.html#sysvar_innodb_autoinc_lock_mode">
<code class="literal">
innodb_autoinc_lock_mode=2
</code>
</a>
.
For more information, See
<a class="xref" href="innodb-auto-increment-handling.html" title="17.6.1.6 AUTO_INCREMENT Handling in InnoDB">
Section 17.6.1.6, “AUTO_INCREMENT Handling in InnoDB”
</a>
.
</p>
<p>
<code class="literal">
InnoDB
</code>
fetches the value of a previously
initialized
<code class="literal">
AUTO_INCREMENT
</code>
column without
setting any locks.
</p>
</li>
<li class="listitem">
<p>
If a
<code class="literal">
FOREIGN KEY
</code>
constraint is defined on a
table, any insert, update, or delete that requires the
constraint condition to be checked sets shared record-level
locks on the records that it looks at to check the constraint.
<code class="literal">
InnoDB
</code>
also sets these locks in the case
where the constraint fails.
</p>
</li>
<li class="listitem">
<p>
<a class="link" href="lock-tables.html" title="15.3.6 LOCK TABLES and UNLOCK TABLES Statements">
<code class="literal">
LOCK TABLES
</code>
</a>
sets table locks,
but it is the higher MySQL layer above the
<code class="literal">
InnoDB
</code>
layer that sets these locks.
<code class="literal">
InnoDB
</code>
is aware of table locks if
<code class="literal">
innodb_table_locks = 1
</code>
(the default) and
<a class="link" href="server-system-variables.html#sysvar_autocommit">
<code class="literal">
autocommit = 0
</code>
</a>
, and the MySQL
layer above
<code class="literal">
InnoDB
</code>
knows about row-level
locks.
</p>
<p>
Otherwise,
<code class="literal">
InnoDB
</code>
's automatic deadlock
detection cannot detect deadlocks where such table locks are
involved. Also, because in this case the higher MySQL layer
does not know about row-level locks, it is possible to get a
table lock on a table where another session currently has
row-level locks. However, this does not endanger transaction
integrity, as discussed in
<a class="xref" href="innodb-deadlock-detection.html" title="17.7.5.2 Deadlock Detection">
Section 17.7.5.2, “Deadlock Detection”
</a>
.
</p>
</li>
<li class="listitem">
<p>
<a class="link" href="lock-tables.html" title="15.3.6 LOCK TABLES and UNLOCK TABLES Statements">
<code class="literal">
LOCK TABLES
</code>
</a>
acquires two locks
on each table if
<code class="literal">
innodb_table_locks=1
</code>
(the
default). In addition to a table lock on the MySQL layer, it
also acquires an
<code class="literal">
InnoDB
</code>
table lock. To
avoid acquiring
<code class="literal">
InnoDB
</code>
table locks, set
<code class="literal">
innodb_table_locks=0
</code>
. If no
<code class="literal">
InnoDB
</code>
table lock is acquired,
<a class="link" href="lock-tables.html" title="15.3.6 LOCK TABLES and UNLOCK TABLES Statements">
<code class="literal">
LOCK TABLES
</code>
</a>
completes even if
some records of the tables are being locked by other
transactions.
</p>
<p>
In MySQL 8.4,
<a class="link" href="innodb-parameters.html#sysvar_innodb_table_locks">
<code class="literal">
innodb_table_locks=0
</code>
</a>
has no
effect for tables locked explicitly with
<a class="link" href="lock-tables.html" title="15.3.6 LOCK TABLES and UNLOCK TABLES Statements">
<code class="literal">
LOCK TABLES ...
WRITE
</code>
</a>
. It does have an effect for tables locked for
read or write by
<a class="link" href="lock-tables.html" title="15.3.6 LOCK TABLES and UNLOCK TABLES Statements">
<code class="literal">
LOCK TABLES ...
WRITE
</code>
</a>
implicitly (for example, through triggers) or
by
<a class="link" href="lock-tables.html" title="15.3.6 LOCK TABLES and UNLOCK TABLES Statements">
<code class="literal">
LOCK TABLES
... READ
</code>
</a>
.
</p>
</li>
<li class="listitem">
<p>
All
<code class="literal">
InnoDB
</code>
locks held by a transaction are
released when the transaction is committed or aborted. Thus,
it does not make much sense to invoke
<a class="link" href="lock-tables.html" title="15.3.6 LOCK TABLES and UNLOCK TABLES Statements">
<code class="literal">
LOCK TABLES
</code>
</a>
on
<code class="literal">
InnoDB
</code>
tables in
<a class="link" href="server-system-variables.html#sysvar_autocommit">
<code class="literal">
autocommit=1
</code>
</a>
mode because the
acquired
<code class="literal">
InnoDB
</code>
table locks would be
released immediately.
</p>
</li>
<li class="listitem">
<p>
You cannot lock additional tables in the middle of a
transaction because
<a class="link" href="lock-tables.html" title="15.3.6 LOCK TABLES and UNLOCK TABLES Statements">
<code class="literal">
LOCK TABLES
</code>
</a>
performs an implicit
<a class="link" href="commit.html" title="15.3.1 START TRANSACTION, COMMIT, and ROLLBACK Statements">
<code class="literal">
COMMIT
</code>
</a>
and
<a class="link" href="lock-tables.html" title="15.3.6 LOCK TABLES and UNLOCK TABLES Statements">
<code class="literal">
UNLOCK
TABLES
</code>
</a>
.
</p>
</li>
</ul>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/table-scan-avoidance.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="table-scan-avoidance">
</a>
10.2.1.23 Avoiding Full Table Scans
</h4>
</div>
</div>
</div>
<a class="indexterm" name="idm46045228443712">
</a>
<a class="indexterm" name="idm46045228442256">
</a>
<a class="indexterm" name="idm46045228440768">
</a>
<p>
The output from
<a class="link" href="explain.html" title="15.8.2 EXPLAIN Statement">
<code class="literal">
EXPLAIN
</code>
</a>
shows
<a class="link" href="explain-output.html#jointype_all">
<code class="literal">
ALL
</code>
</a>
in the
<code class="literal">
type
</code>
column when MySQL uses a
<a class="link" href="glossary.html#glos_full_table_scan" title="full table scan">
full table scan
</a>
to
resolve a query. This usually happens under the following
conditions:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
The table is so small that it is faster to perform a table
scan than to bother with a key lookup. This is common for
tables with fewer than 10 rows and a short row length.
</p>
</li>
<li class="listitem">
<p>
There are no usable restrictions in the
<code class="literal">
ON
</code>
or
<code class="literal">
WHERE
</code>
clause
for indexed columns.
</p>
</li>
<li class="listitem">
<p>
You are comparing indexed columns with constant values and
MySQL has calculated (based on the index tree) that the
constants cover too large a part of the table and that a
table scan would be faster. See
<a class="xref" href="where-optimization.html" title="10.2.1.1 WHERE Clause Optimization">
Section 10.2.1.1, “WHERE Clause Optimization”
</a>
.
</p>
</li>
<li class="listitem">
<p>
You are using a key with low cardinality (many rows match
the key value) through another column. In this case, MySQL
assumes that by using the key probably requires many key
lookups and that a table scan would be faster.
</p>
</li>
</ul>
</div>
<p>
For small tables, a table scan often is appropriate and the
performance impact is negligible. For large tables, try the
following techniques to avoid having the optimizer incorrectly
choose a table scan:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
Use
<code class="literal">
ANALYZE TABLE
<em class="replaceable">
<code>
tbl_name
</code>
</em>
</code>
to update
the key distributions for the scanned table. See
<a class="xref" href="analyze-table.html" title="15.7.3.1 ANALYZE TABLE Statement">
Section 15.7.3.1, “ANALYZE TABLE Statement”
</a>
.
</p>
</li>
<li class="listitem">
<p>
Use
<code class="literal">
FORCE INDEX
</code>
for the scanned table
to tell MySQL that table scans are very expensive compared
to using the given index:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa94466196"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> t1<span class="token punctuation">,</span> t2 <span class="token keyword">FORCE</span> <span class="token keyword">INDEX</span> <span class="token punctuation">(</span><em class="replaceable">index_for_column</em><span class="token punctuation">)</span>
<span class="token keyword">WHERE</span> t1<span class="token punctuation">.</span><em class="replaceable">col_name</em><span class="token operator">=</span>t2<span class="token punctuation">.</span><em class="replaceable">col_name</em><span class="token punctuation">;</span></code></pre>
</div>
<p>
See
<a class="xref" href="index-hints.html" title="10.9.4 Index Hints">
Section 10.9.4, “Index Hints”
</a>
.
</p>
</li>
<li class="listitem">
<p>
Start
<a class="link" href="mysqld.html" title="6.3.1 mysqld — The MySQL Server">
<span class="command">
<strong>
mysqld
</strong>
</span>
</a>
with the
<a class="link" href="server-system-variables.html#sysvar_max_seeks_for_key">
<code class="option">
--max-seeks-for-key=1000
</code>
</a>
option or use
<code class="literal">
SET
max_seeks_for_key=1000
</code>
to tell the optimizer to
assume that no key scan causes more than 1,000 key seeks.
See
<a class="xref" href="server-system-variables.html" title="7.1.8 Server System Variables">
Section 7.1.8, “Server System Variables”
</a>
.
</p>
</li>
</ul>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/group-replication-server-states.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="group-replication-server-states">
</a>
20.4.2 Group Replication Server States
</h3>
</div>
</div>
</div>
<a class="indexterm" name="idm46045133688736">
</a>
<p>
The state of a Group Replication group member shows its current
role in the group. The Performance Schema table
<a class="link" href="performance-schema-replication-group-members-table.html" title="29.12.11.16 The replication_group_members Table">
<code class="literal">
replication_group_members
</code>
</a>
shows the
state for each member in a group. If the group is fully functional
and all members are communicating properly, all members report the
same state for all other members. However, a member that has left
the group or is part of a network partition cannot report accurate
information on the other servers. In this situation, the member
does not attempt to guess the status of the other servers, and
instead reports them as unreachable.
</p>
<p>
A group member can be in the following states:
</p>
<div class="variablelist">
<dl class="variablelist">
<dt>
<span class="term">
<code class="literal">
ONLINE
</code>
</span>
</dt>
<dd>
<p>
The server is an active member of a group and in a fully
functioning state. Other group members can connect to it, as
can clients if applicable. A member is only fully
synchronized with the group, and participating in it, when
it is in the
<code class="literal">
ONLINE
</code>
state.
</p>
</dd>
<dt>
<span class="term">
<code class="literal">
RECOVERING
</code>
</span>
</dt>
<dd>
<p>
The server has joined a group and is in the process of
becoming an active member. Distributed recovery is currently
taking place, where the member is receiving state transfer
from a donor using a remote cloning operation or the donor's
binary log. This state is
</p>
<p>
For more information, see
<a class="xref" href="group-replication-distributed-recovery.html" title="20.5.4 Distributed Recovery">
Section 20.5.4, “Distributed Recovery”
</a>
.
</p>
</dd>
<dt>
<span class="term">
<code class="literal">
OFFLINE
</code>
</span>
</dt>
<dd>
<p>
The Group Replication plugin is loaded but the member does
not belong to any group. This status may briefly occur while
a member is joining or rejoining a group.
</p>
</dd>
<dt>
<span class="term">
<code class="literal">
ERROR
</code>
</span>
</dt>
<dd>
<p>
The member is in an error state and is not functioning
correctly as a group member. A member can enter error state
either while applying transactions or during the recovery
phase. A member in this state does not participate in the
group's transactions. For more information on possible
reasons for error states, see
<a class="xref" href="group-replication-responses-failure.html" title="20.7.7 Responses to Failure Detection and Network Partitioning">
Section 20.7.7, “Responses to Failure Detection and Network Partitioning”
</a>
.
</p>
<p>
Depending on the exit action set by
<a class="link" href="group-replication-system-variables.html#sysvar_group_replication_exit_state_action">
<code class="literal">
group_replication_exit_state_action
</code>
</a>
,
the member is in read-only mode
(
<a class="link" href="server-system-variables.html#sysvar_super_read_only">
<code class="literal">
super_read_only=ON
</code>
</a>
) and
could also be in offline mode
(
<a class="link" href="server-system-variables.html#sysvar_offline_mode">
<code class="literal">
offline_mode=ON
</code>
</a>
). Note
that a server in offline mode following the
<code class="literal">
OFFLINE_MODE
</code>
exit action is displayed
with
<code class="literal">
ERROR
</code>
status, not
<code class="literal">
OFFLINE
</code>
. A server with the exit action
<code class="literal">
ABORT_SERVER
</code>
shuts down and is removed
from the view of the group. For more information, see
<a class="xref" href="group-replication-responses-failure-exit.html" title="20.7.7.4 Exit Action">
Section 20.7.7.4, “Exit Action”
</a>
.
</p>
<p>
While a member is joining or rejoining a replication group,
its status can be displayed as
<code class="literal">
ERROR
</code>
before the group completes the compatibility checks and
accepts it as a member.
</p>
</dd>
<dt>
<span class="term">
<code class="literal">
UNREACHABLE
</code>
</span>
</dt>
<dd>
<p>
The local failure detector suspects that the member cannot
be contacted, because the group's messages are timing out.
This can happen if a member is disconnected involuntarily,
for example. If you see this status for other servers, it
can also mean that the member where you query this table is
part of a partition, where a subset of the group's servers
can contact each other but cannot contact the other servers
in the group. For more information, see
<a class="xref" href="group-replication-network-partitioning.html" title="20.7.8 Handling a Network Partition and Loss of Quorum">
Section 20.7.8, “Handling a Network Partition and Loss of Quorum”
</a>
.
</p>
</dd>
</dl>
</div>
<p>
See
<a class="xref" href="group-replication-replication-group-members.html" title="20.4.3 The replication_group_members Table">
Section 20.4.3, “The replication_group_members Table”
</a>
for an example of the Performance Schema table contents.
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/mysql-cluster-limitations-error-handling.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="mysql-cluster-limitations-error-handling">
</a>
25.2.7.4 NDB Cluster Error Handling
</h4>
</div>
</div>
</div>
<a class="indexterm" name="idm46045123321264">
</a>
<p>
Starting, stopping, or restarting a node may give rise to
temporary errors causing some transactions to fail. These
include the following cases:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<b>
Temporary errors.
</b>
When first starting a node, it is possible that you may
see Error 1204
<span class="errortext">
Temporary failure, distribution
changed
</span>
and similar temporary errors.
</p>
</li>
<li class="listitem">
<p>
<b>
Errors due to node failure.
</b>
The stopping or failure of any data node can result in a
number of different node failure errors. (However, there
should be no aborted transactions when performing a
planned shutdown of the cluster.)
</p>
</li>
</ul>
</div>
<p>
In either of these cases, any errors that are generated must be
handled within the application. This should be done by retrying
the transaction.
</p>
<p>
See also
<a class="xref" href="mysql-cluster-limitations-limits.html" title="25.2.7.2 Limits and Differences of NDB Cluster from Standard MySQL Limits">
Section 25.2.7.2, “Limits and Differences of NDB Cluster from Standard MySQL Limits”
</a>
.
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/replication-statements-source.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="replication-statements-source">
</a>
15.4.1 SQL Statements for Controlling Source Servers
</h3>
</div>
</div>
</div>
<div class="toc">
<dl class="toc">
<dt>
<span class="section">
<a href="purge-binary-logs.html">
15.4.1.1 PURGE BINARY LOGS Statement
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="reset-binary-logs-and-gtids.html">
15.4.1.2 RESET BINARY LOGS AND GTIDS Statement
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="set-sql-log-bin.html">
15.4.1.3 SET sql_log_bin Statement
</a>
</span>
</dt>
</dl>
</div>
<a class="indexterm" name="idm46045177915248">
</a>
<a class="indexterm" name="idm46045177913760">
</a>
<a class="indexterm" name="idm46045177912272">
</a>
<p>
This section discusses statements for managing replication source
servers.
<a class="xref" href="replication-statements-replica.html" title="15.4.2 SQL Statements for Controlling Replica Servers">
Section 15.4.2, “SQL Statements for Controlling Replica Servers”
</a>
,
discusses statements for managing replica servers.
</p>
<p>
In addition to the statements described here, the following
<a class="link" href="show.html" title="15.7.7 SHOW Statements">
<code class="literal">
SHOW
</code>
</a>
statements are used with
source servers in replication. For information about these
statements, see
<a class="xref" href="show.html" title="15.7.7 SHOW Statements">
Section 15.7.7, “SHOW Statements”
</a>
.
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<a class="link" href="show-binary-logs.html" title="15.7.7.2 SHOW BINARY LOGS Statement">
<code class="literal">
SHOW BINARY LOGS
</code>
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="link" href="show-binlog-events.html" title="15.7.7.3 SHOW BINLOG EVENTS Statement">
<code class="literal">
SHOW BINLOG EVENTS
</code>
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="link" href="show-binary-log-status.html" title="15.7.7.1 SHOW BINARY LOG STATUS Statement">
<code class="literal">
SHOW BINARY LOG STATUS
</code>
</a>
(replaces
<code class="literal">
SHOW MASTER STATUS
</code>
, which is no
longer supported)
</p>
</li>
<li class="listitem">
<p>
<a class="link" href="show-replicas.html" title="15.7.7.36 SHOW REPLICAS Statement">
<code class="literal">
SHOW
REPLICAS
</code>
</a>
</p>
</li>
</ul>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/optimize-table.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="optimize-table">
</a>
15.7.3.4 OPTIMIZE TABLE Statement
</h4>
</div>
</div>
</div>
<a class="indexterm" name="idm46045172207008">
</a>
<a class="indexterm" name="idm46045172205952">
</a>
<a class="indexterm" name="idm46045172204464">
</a>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa59377275"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">OPTIMIZE</span> <span class="token punctuation">[</span><span class="token keyword">NO_WRITE_TO_BINLOG</span> <span class="token operator">|</span> <span class="token keyword">LOCAL</span><span class="token punctuation">]</span>
<span class="token keyword">TABLE</span> <em class="replaceable">tbl_name</em> <span class="token punctuation">[</span><span class="token punctuation">,</span> <em class="replaceable">tbl_name</em><span class="token punctuation">]</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span></code></pre>
</div>
<p>
<a class="link" href="optimize-table.html" title="15.7.3.4 OPTIMIZE TABLE Statement">
<code class="literal">
OPTIMIZE TABLE
</code>
</a>
reorganizes the
physical storage of table data and associated index data, to
reduce storage space and improve I/O efficiency when accessing
the table. The exact changes made to each table depend on the
<a class="link" href="glossary.html#glos_storage_engine" title="storage engine">
storage engine
</a>
used
by that table.
</p>
<p>
Use
<a class="link" href="optimize-table.html" title="15.7.3.4 OPTIMIZE TABLE Statement">
<code class="literal">
OPTIMIZE TABLE
</code>
</a>
in these
cases, depending on the type of table:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
After doing substantial insert, update, or delete operations
on an
<code class="literal">
InnoDB
</code>
table that has its own
<a class="link" href="glossary.html#glos_ibd_file" title=".ibd file">
.ibd file
</a>
because it
was created with the
<a class="link" href="innodb-parameters.html#sysvar_innodb_file_per_table">
<code class="literal">
innodb_file_per_table
</code>
</a>
option enabled. The table and indexes are reorganized, and
disk space can be reclaimed for use by the operating system.
</p>
</li>
<li class="listitem">
<p>
After doing substantial insert, update, or delete operations
on columns that are part of a
<code class="literal">
FULLTEXT
</code>
index in an
<code class="literal">
InnoDB
</code>
table. Set the
configuration option
<a class="link" href="innodb-parameters.html#sysvar_innodb_optimize_fulltext_only">
<code class="literal">
innodb_optimize_fulltext_only=1
</code>
</a>
first. To keep the index maintenance period to a reasonable
time, set the
<a class="link" href="innodb-parameters.html#sysvar_innodb_ft_num_word_optimize">
<code class="literal">
innodb_ft_num_word_optimize
</code>
</a>
option to specify how many words to update in the search
index, and run a sequence of
<code class="literal">
OPTIMIZE
TABLE
</code>
statements until the search index is fully
updated.
</p>
</li>
<li class="listitem">
<p>
After deleting a large part of a
<code class="literal">
MyISAM
</code>
or
<code class="literal">
ARCHIVE
</code>
table, or making many changes
to a
<code class="literal">
MyISAM
</code>
or
<code class="literal">
ARCHIVE
</code>
table with variable-length rows (tables that have
<a class="link" href="char.html" title="13.3.2 The CHAR and VARCHAR Types">
<code class="literal">
VARCHAR
</code>
</a>
,
<a class="link" href="binary-varbinary.html" title="13.3.3 The BINARY and VARBINARY Types">
<code class="literal">
VARBINARY
</code>
</a>
,
<a class="link" href="blob.html" title="13.3.4 The BLOB and TEXT Types">
<code class="literal">
BLOB
</code>
</a>
, or
<a class="link" href="blob.html" title="13.3.4 The BLOB and TEXT Types">
<code class="literal">
TEXT
</code>
</a>
columns). Deleted rows
are maintained in a linked list and subsequent
<a class="link" href="insert.html" title="15.2.7 INSERT Statement">
<code class="literal">
INSERT
</code>
</a>
operations reuse old
row positions. You can use
<a class="link" href="optimize-table.html" title="15.7.3.4 OPTIMIZE TABLE Statement">
<code class="literal">
OPTIMIZE
TABLE
</code>
</a>
to reclaim the unused space and to
defragment the data file. After extensive changes to a
table, this statement may also improve performance of
statements that use the table, sometimes significantly.
</p>
</li>
</ul>
</div>
<p>
This statement requires
<a class="link" href="privileges-provided.html#priv_select">
<code class="literal">
SELECT
</code>
</a>
and
<a class="link" href="privileges-provided.html#priv_insert">
<code class="literal">
INSERT
</code>
</a>
privileges for the
table.
</p>
<p>
<a class="link" href="optimize-table.html" title="15.7.3.4 OPTIMIZE TABLE Statement">
<code class="literal">
OPTIMIZE TABLE
</code>
</a>
works for
<a class="link" href="innodb-storage-engine.html" title="Chapter 17 The InnoDB Storage Engine">
<code class="literal">
InnoDB
</code>
</a>
,
<a class="link" href="myisam-storage-engine.html" title="18.2 The MyISAM Storage Engine">
<code class="literal">
MyISAM
</code>
</a>
, and
<a class="link" href="archive-storage-engine.html" title="18.5 The ARCHIVE Storage Engine">
<code class="literal">
ARCHIVE
</code>
</a>
tables.
<a class="link" href="optimize-table.html" title="15.7.3.4 OPTIMIZE TABLE Statement">
<code class="literal">
OPTIMIZE TABLE
</code>
</a>
is also supported
for dynamic columns of in-memory
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDB
</code>
</a>
tables. It does not work for
fixed-width columns of in-memory tables, nor does it work for
Disk Data tables. The performance of
<code class="literal">
OPTIMIZE
</code>
on NDB Cluster tables can be tuned using
<a class="link" href="mysql-cluster-options-variables.html#option_mysqld_ndb-optimization-delay">
<code class="option">
--ndb-optimization-delay
</code>
</a>
, which
controls the length of time to wait between processing batches
of rows by
<a class="link" href="optimize-table.html" title="15.7.3.4 OPTIMIZE TABLE Statement">
<code class="literal">
OPTIMIZE TABLE
</code>
</a>
. For
more information, see
<a class="xref" href="mysql-cluster-limitations-resolved.html" title="25.2.7.11 Previous NDB Cluster Issues Resolved in NDB Cluster 8.4">
Section 25.2.7.11, “Previous NDB Cluster Issues Resolved in NDB Cluster 8.4”
</a>
.
</p>
<p>
For NDB Cluster tables,
<a class="link" href="optimize-table.html" title="15.7.3.4 OPTIMIZE TABLE Statement">
<code class="literal">
OPTIMIZE
TABLE
</code>
</a>
can be interrupted by (for example) killing the
SQL thread performing the
<code class="literal">
OPTIMIZE
</code>
operation.
</p>
<p>
By default,
<a class="link" href="optimize-table.html" title="15.7.3.4 OPTIMIZE TABLE Statement">
<code class="literal">
OPTIMIZE TABLE
</code>
</a>
does
<span class="emphasis">
<em>
not
</em>
</span>
work for tables created using any other
storage engine and returns a result indicating this lack of
support. You can make
<a class="link" href="optimize-table.html" title="15.7.3.4 OPTIMIZE TABLE Statement">
<code class="literal">
OPTIMIZE
TABLE
</code>
</a>
work for other storage engines by starting
<a class="link" href="mysqld.html" title="6.3.1 mysqld — The MySQL Server">
<span class="command">
<strong>
mysqld
</strong>
</span>
</a>
with the
<a class="link" href="server-options.html#option_mysqld_skip-new">
<code class="option">
--skip-new
</code>
</a>
option. In this case,
<a class="link" href="optimize-table.html" title="15.7.3.4 OPTIMIZE TABLE Statement">
<code class="literal">
OPTIMIZE TABLE
</code>
</a>
is just mapped to
<a class="link" href="alter-table.html" title="15.1.9 ALTER TABLE Statement">
<code class="literal">
ALTER TABLE
</code>
</a>
.
</p>
<p>
This statement does not work with views.
</p>
<p>
<a class="link" href="optimize-table.html" title="15.7.3.4 OPTIMIZE TABLE Statement">
<code class="literal">
OPTIMIZE TABLE
</code>
</a>
is supported for
partitioned tables. For information about using this statement
with partitioned tables and table partitions, see
<a class="xref" href="partitioning-maintenance.html" title="26.3.4 Maintenance of Partitions">
Section 26.3.4, “Maintenance of Partitions”
</a>
.
</p>
<p>
By default, the server writes
<a class="link" href="optimize-table.html" title="15.7.3.4 OPTIMIZE TABLE Statement">
<code class="literal">
OPTIMIZE
TABLE
</code>
</a>
statements to the binary log so that they
replicate to replicas. To suppress logging, specify the optional
<code class="literal">
NO_WRITE_TO_BINLOG
</code>
keyword or its alias
<code class="literal">
LOCAL
</code>
. You must have the
<a class="link" href="privileges-provided.html#priv_optimize-local-table">
<code class="literal">
OPTIMIZE_LOCAL_TABLE
</code>
</a>
privilege to
use this option.
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<a class="xref" href="optimize-table.html#optimize-table-output" title="OPTIMIZE TABLE Output">
OPTIMIZE TABLE Output
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="optimize-table.html#optimize-table-innodb-details" title="InnoDB Details">
InnoDB Details
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="optimize-table.html#optimize-table-myisam-details" title="MyISAM Details">
MyISAM Details
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="optimize-table.html#optimize-table-other-considerations" title="Other Considerations">
Other Considerations
</a>
</p>
</li>
</ul>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h5 class="title">
<a name="optimize-table-output">
</a>
OPTIMIZE TABLE Output
</h5>
</div>
</div>
</div>
<p>
<a class="link" href="optimize-table.html" title="15.7.3.4 OPTIMIZE TABLE Statement">
<code class="literal">
OPTIMIZE TABLE
</code>
</a>
returns a result
set with the columns shown in the following table.
</p>
<div class="informaltable">
<table summary="Columns of the OPTIMIZE TABLE result set.">
<colgroup>
<col style="width: 15%"/>
<col style="width: 60%"/>
</colgroup>
<thead>
<tr>
<th>
Column
</th>
<th>
Value
</th>
</tr>
</thead>
<tbody>
<tr>
<td>
<code class="literal">
Table
</code>
</td>
<td>
The table name
</td>
</tr>
<tr>
<td>
<code class="literal">
Op
</code>
</td>
<td>
Always
<code class="literal">
optimize
</code>
</td>
</tr>
<tr>
<td>
<code class="literal">
Msg_type
</code>
</td>
<td>
<code class="literal">
status
</code>
,
<code class="literal">
error
</code>
,
<code class="literal">
info
</code>
,
<code class="literal">
note
</code>
, or
<code class="literal">
warning
</code>
</td>
</tr>
<tr>
<td>
<code class="literal">
Msg_text
</code>
</td>
<td>
An informational message
</td>
</tr>
</tbody>
</table>
</div>
<p>
<a class="link" href="optimize-table.html" title="15.7.3.4 OPTIMIZE TABLE Statement">
<code class="literal">
OPTIMIZE TABLE
</code>
</a>
table catches
and throws any errors that occur while copying table
statistics from the old file to the newly created file. For
example. if the user ID of the owner of the
<code class="filename">
.MYD
</code>
or
<code class="filename">
.MYI
</code>
file is
different from the user ID of the
<a class="link" href="mysqld.html" title="6.3.1 mysqld — The MySQL Server">
<span class="command">
<strong>
mysqld
</strong>
</span>
</a>
process,
<a class="link" href="optimize-table.html" title="15.7.3.4 OPTIMIZE TABLE Statement">
<code class="literal">
OPTIMIZE TABLE
</code>
</a>
generates a "cannot change ownership of the file" error unless
<a class="link" href="mysqld.html" title="6.3.1 mysqld — The MySQL Server">
<span class="command">
<strong>
mysqld
</strong>
</span>
</a>
is started by the
<code class="literal">
root
</code>
user.
</p>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h5 class="title">
<a name="optimize-table-innodb-details">
</a>
InnoDB Details
</h5>
</div>
</div>
</div>
<p>
For
<code class="literal">
InnoDB
</code>
tables,
<a class="link" href="optimize-table.html" title="15.7.3.4 OPTIMIZE TABLE Statement">
<code class="literal">
OPTIMIZE TABLE
</code>
</a>
is mapped to
<a class="link" href="alter-table.html" title="15.1.9 ALTER TABLE Statement">
<code class="literal">
ALTER TABLE ...
FORCE
</code>
</a>
, which rebuilds the table to update index
statistics and free unused space in the clustered index. This
is displayed in the output of
<a class="link" href="optimize-table.html" title="15.7.3.4 OPTIMIZE TABLE Statement">
<code class="literal">
OPTIMIZE
TABLE
</code>
</a>
when you run it on an
<code class="literal">
InnoDB
</code>
table, as shown here:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa98160816"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">OPTIMIZE</span> <span class="token keyword">TABLE</span> foo<span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> Table <span class="token punctuation">|</span> Op <span class="token punctuation">|</span> Msg_type <span class="token punctuation">|</span> Msg_text <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> test.foo <span class="token punctuation">|</span> optimize <span class="token punctuation">|</span> note <span class="token punctuation">|</span> Table does not support optimize, doing recreate <span class="token punctuation">+</span> analyze instead <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> test.foo <span class="token punctuation">|</span> optimize <span class="token punctuation">|</span> status <span class="token punctuation">|</span> OK <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span></code></pre>
</div>
<p>
<a class="link" href="optimize-table.html" title="15.7.3.4 OPTIMIZE TABLE Statement">
<code class="literal">
OPTIMIZE TABLE
</code>
</a>
uses
<a class="link" href="innodb-online-ddl.html" title="17.12 InnoDB and Online DDL">
online DDL
</a>
for
regular and partitioned
<code class="literal">
InnoDB
</code>
tables,
which reduces downtime for concurrent DML operations. The
table rebuild triggered by
<a class="link" href="optimize-table.html" title="15.7.3.4 OPTIMIZE TABLE Statement">
<code class="literal">
OPTIMIZE
TABLE
</code>
</a>
is completed in place. An exclusive table lock
is only taken briefly during the prepare phase and the commit
phase of the operation. During the prepare phase, metadata is
updated and an intermediate table is created. During the
commit phase, table metadata changes are committed.
</p>
<p>
<a class="link" href="optimize-table.html" title="15.7.3.4 OPTIMIZE TABLE Statement">
<code class="literal">
OPTIMIZE TABLE
</code>
</a>
rebuilds the
table using the table copy method under the following
conditions:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
When the
<a class="link" href="server-system-variables.html#sysvar_old_alter_table">
<code class="literal">
old_alter_table
</code>
</a>
system variable is enabled.
</p>
</li>
<li class="listitem">
<p>
When the server is started with the
<a class="link" href="server-options.html#option_mysqld_skip-new">
<code class="option">
--skip-new
</code>
</a>
option.
</p>
</li>
</ul>
</div>
<p>
<a class="link" href="optimize-table.html" title="15.7.3.4 OPTIMIZE TABLE Statement">
<code class="literal">
OPTIMIZE TABLE
</code>
</a>
using
<a class="link" href="innodb-online-ddl.html" title="17.12 InnoDB and Online DDL">
online DDL
</a>
is not
supported for
<code class="literal">
InnoDB
</code>
tables that contain
<code class="literal">
FULLTEXT
</code>
indexes. The table copy method is
used instead.
</p>
<p>
<code class="literal">
InnoDB
</code>
stores data using a page-allocation
method and does not suffer from fragmentation in the same way
that legacy storage engines (such as
<code class="literal">
MyISAM
</code>
) do. When considering whether or not
to run optimize, consider the workload of transactions that
your server is expected to process:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
Some level of fragmentation is expected.
<code class="literal">
InnoDB
</code>
only fills
<a class="link" href="glossary.html#glos_page" title="page">
pages
</a>
93% full, to
leave room for updates without having to split pages.
</p>
</li>
<li class="listitem">
<p>
Delete operations might leave gaps that leave pages less
filled than desired, which could make it worthwhile to
optimize the table.
</p>
</li>
<li class="listitem">
<p>
Updates to rows usually rewrite the data within the same
page, depending on the data type and row format, when
sufficient space is available. See
<a class="xref" href="innodb-compression-internals.html" title="17.9.1.5 How Compression Works for InnoDB Tables">
Section 17.9.1.5, “How Compression Works for InnoDB Tables”
</a>
and
<a class="xref" href="innodb-row-format.html" title="17.10 InnoDB Row Formats">
Section 17.10, “InnoDB Row Formats”
</a>
.
</p>
</li>
<li class="listitem">
<p>
High-concurrency workloads might leave gaps in indexes
over time, as
<code class="literal">
InnoDB
</code>
retains multiple
versions of the same data due through its
<a class="link" href="glossary.html#glos_mvcc" title="MVCC">
MVCC
</a>
mechanism. See
<a class="xref" href="innodb-multi-versioning.html" title="17.3 InnoDB Multi-Versioning">
Section 17.3, “InnoDB Multi-Versioning”
</a>
.
</p>
</li>
</ul>
</div>
<p>
</p>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h5 class="title">
<a name="optimize-table-myisam-details">
</a>
MyISAM Details
</h5>
</div>
</div>
</div>
<p>
For
<code class="literal">
MyISAM
</code>
tables,
<a class="link" href="optimize-table.html" title="15.7.3.4 OPTIMIZE TABLE Statement">
<code class="literal">
OPTIMIZE TABLE
</code>
</a>
works as
follows:
</p>
<div class="orderedlist">
<ol class="orderedlist" type="1">
<li class="listitem">
<p>
If the table has deleted or split rows, repair the table.
</p>
</li>
<li class="listitem">
<p>
If the index pages are not sorted, sort them.
</p>
</li>
<li class="listitem">
<p>
If the table's statistics are not up to date (and the
repair could not be accomplished by sorting the index),
update them.
</p>
</li>
</ol>
</div>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h5 class="title">
<a name="optimize-table-other-considerations">
</a>
Other Considerations
</h5>
</div>
</div>
</div>
<p>
<a class="link" href="optimize-table.html" title="15.7.3.4 OPTIMIZE TABLE Statement">
<code class="literal">
OPTIMIZE TABLE
</code>
</a>
is performed
online for regular and partitioned
<code class="literal">
InnoDB
</code>
tables. Otherwise, MySQL
<a class="link" href="glossary.html#glos_table_lock" title="table lock">
locks
the table
</a>
during the time
<a class="link" href="optimize-table.html" title="15.7.3.4 OPTIMIZE TABLE Statement">
<code class="literal">
OPTIMIZE
TABLE
</code>
</a>
is running.
</p>
<p>
<a class="link" href="optimize-table.html" title="15.7.3.4 OPTIMIZE TABLE Statement">
<code class="literal">
OPTIMIZE TABLE
</code>
</a>
does not sort
R-tree indexes, such as spatial indexes on
<code class="literal">
POINT
</code>
columns. (Bug #23578)
</p>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/json-function-reference.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="json-function-reference">
</a>
14.17.1 JSON Function Reference
</h3>
</div>
</div>
</div>
<a class="indexterm" name="idm46045195828192">
</a>
<div class="table">
<a name="idm46045195827120">
</a>
<p class="title">
<b>
Table 14.22 JSON Functions
</b>
</p>
<div class="table-contents">
<table frame="box" rules="all" summary="A reference that lists all JSON functions.">
<colgroup>
<col style="width: 25%"/>
<col style="width: 62%"/>
<col style="width: 12%"/>
</colgroup>
<thead>
<tr>
<th>
Name
</th>
<th>
Description
</th>
<th>
Deprecated
</th>
</tr>
</thead>
<tbody>
<tr>
<th scope="row">
<a class="link" href="json-search-functions.html#operator_json-column-path">
<code class="literal">
->
</code>
</a>
</th>
<td>
Return value from JSON column after evaluating path; equivalent to
JSON_EXTRACT().
</td>
<td>
</td>
</tr>
<tr>
<th scope="row">
<a class="link" href="json-search-functions.html#operator_json-inline-path">
<code class="literal">
->>
</code>
</a>
</th>
<td>
Return value from JSON column after evaluating path and unquoting
the result; equivalent to JSON_UNQUOTE(JSON_EXTRACT()).
</td>
<td>
</td>
</tr>
<tr>
<th scope="row">
<a class="link" href="json-creation-functions.html#function_json-array">
<code class="literal">
JSON_ARRAY()
</code>
</a>
</th>
<td>
Create JSON array
</td>
<td>
</td>
</tr>
<tr>
<th scope="row">
<a class="link" href="json-modification-functions.html#function_json-array-append">
<code class="literal">
JSON_ARRAY_APPEND()
</code>
</a>
</th>
<td>
Append data to JSON document
</td>
<td>
</td>
</tr>
<tr>
<th scope="row">
<a class="link" href="json-modification-functions.html#function_json-array-insert">
<code class="literal">
JSON_ARRAY_INSERT()
</code>
</a>
</th>
<td>
Insert into JSON array
</td>
<td>
</td>
</tr>
<tr>
<th scope="row">
<a class="link" href="json-search-functions.html#function_json-contains">
<code class="literal">
JSON_CONTAINS()
</code>
</a>
</th>
<td>
Whether JSON document contains specific object at path
</td>
<td>
</td>
</tr>
<tr>
<th scope="row">
<a class="link" href="json-search-functions.html#function_json-contains-path">
<code class="literal">
JSON_CONTAINS_PATH()
</code>
</a>
</th>
<td>
Whether JSON document contains any data at path
</td>
<td>
</td>
</tr>
<tr>
<th scope="row">
<a class="link" href="json-attribute-functions.html#function_json-depth">
<code class="literal">
JSON_DEPTH()
</code>
</a>
</th>
<td>
Maximum depth of JSON document
</td>
<td>
</td>
</tr>
<tr>
<th scope="row">
<a class="link" href="json-search-functions.html#function_json-extract">
<code class="literal">
JSON_EXTRACT()
</code>
</a>
</th>
<td>
Return data from JSON document
</td>
<td>
</td>
</tr>
<tr>
<th scope="row">
<a class="link" href="json-modification-functions.html#function_json-insert">
<code class="literal">
JSON_INSERT()
</code>
</a>
</th>
<td>
Insert data into JSON document
</td>
<td>
</td>
</tr>
<tr>
<th scope="row">
<a class="link" href="json-search-functions.html#function_json-keys">
<code class="literal">
JSON_KEYS()
</code>
</a>
</th>
<td>
Array of keys from JSON document
</td>
<td>
</td>
</tr>
<tr>
<th scope="row">
<a class="link" href="json-attribute-functions.html#function_json-length">
<code class="literal">
JSON_LENGTH()
</code>
</a>
</th>
<td>
Number of elements in JSON document
</td>
<td>
</td>
</tr>
<tr>
<th scope="row">
<a class="link" href="json-modification-functions.html#function_json-merge">
<code class="literal">
JSON_MERGE()
</code>
</a>
</th>
<td>
Merge JSON documents, preserving duplicate keys. Deprecated
synonym for JSON_MERGE_PRESERVE()
</td>
<td>
Yes
</td>
</tr>
<tr>
<th scope="row">
<a class="link" href="json-modification-functions.html#function_json-merge-patch">
<code class="literal">
JSON_MERGE_PATCH()
</code>
</a>
</th>
<td>
Merge JSON documents, replacing values of duplicate keys
</td>
<td>
</td>
</tr>
<tr>
<th scope="row">
<a class="link" href="json-modification-functions.html#function_json-merge-preserve">
<code class="literal">
JSON_MERGE_PRESERVE()
</code>
</a>
</th>
<td>
Merge JSON documents, preserving duplicate keys
</td>
<td>
</td>
</tr>
<tr>
<th scope="row">
<a class="link" href="json-creation-functions.html#function_json-object">
<code class="literal">
JSON_OBJECT()
</code>
</a>
</th>
<td>
Create JSON object
</td>
<td>
</td>
</tr>
<tr>
<th scope="row">
<a class="link" href="json-search-functions.html#function_json-overlaps">
<code class="literal">
JSON_OVERLAPS()
</code>
</a>
</th>
<td>
Compares two JSON documents, returns TRUE (1) if these have any
key-value pairs or array elements in common, otherwise FALSE (0)
</td>
<td>
</td>
</tr>
<tr>
<th scope="row">
<a class="link" href="json-utility-functions.html#function_json-pretty">
<code class="literal">
JSON_PRETTY()
</code>
</a>
</th>
<td>
Print a JSON document in human-readable format
</td>
<td>
</td>
</tr>
<tr>
<th scope="row">
<a class="link" href="json-creation-functions.html#function_json-quote">
<code class="literal">
JSON_QUOTE()
</code>
</a>
</th>
<td>
Quote JSON document
</td>
<td>
</td>
</tr>
<tr>
<th scope="row">
<a class="link" href="json-modification-functions.html#function_json-remove">
<code class="literal">
JSON_REMOVE()
</code>
</a>
</th>
<td>
Remove data from JSON document
</td>
<td>
</td>
</tr>
<tr>
<th scope="row">
<a class="link" href="json-modification-functions.html#function_json-replace">
<code class="literal">
JSON_REPLACE()
</code>
</a>
</th>
<td>
Replace values in JSON document
</td>
<td>
</td>
</tr>
<tr>
<th scope="row">
<a class="link" href="json-validation-functions.html#function_json-schema-valid">
<code class="literal">
JSON_SCHEMA_VALID()
</code>
</a>
</th>
<td>
Validate JSON document against JSON schema; returns TRUE/1 if
document validates against schema, or FALSE/0 if it does not
</td>
<td>
</td>
</tr>
<tr>
<th scope="row">
<a class="link" href="json-validation-functions.html#function_json-schema-validation-report">
<code class="literal">
JSON_SCHEMA_VALIDATION_REPORT()
</code>
</a>
</th>
<td>
Validate JSON document against JSON schema; returns report in JSON
format on outcome on validation including success or failure and
reasons for failure
</td>
<td>
</td>
</tr>
<tr>
<th scope="row">
<a class="link" href="json-search-functions.html#function_json-search">
<code class="literal">
JSON_SEARCH()
</code>
</a>
</th>
<td>
Path to value within JSON document
</td>
<td>
</td>
</tr>
<tr>
<th scope="row">
<a class="link" href="json-modification-functions.html#function_json-set">
<code class="literal">
JSON_SET()
</code>
</a>
</th>
<td>
Insert data into JSON document
</td>
<td>
</td>
</tr>
<tr>
<th scope="row">
<a class="link" href="json-utility-functions.html#function_json-storage-free">
<code class="literal">
JSON_STORAGE_FREE()
</code>
</a>
</th>
<td>
Freed space within binary representation of JSON column value
following partial update
</td>
<td>
</td>
</tr>
<tr>
<th scope="row">
<a class="link" href="json-utility-functions.html#function_json-storage-size">
<code class="literal">
JSON_STORAGE_SIZE()
</code>
</a>
</th>
<td>
Space used for storage of binary representation of a JSON document
</td>
<td>
</td>
</tr>
<tr>
<th scope="row">
<a class="link" href="json-table-functions.html#function_json-table">
<code class="literal">
JSON_TABLE()
</code>
</a>
</th>
<td>
Return data from a JSON expression as a relational table
</td>
<td>
</td>
</tr>
<tr>
<th scope="row">
<a class="link" href="json-attribute-functions.html#function_json-type">
<code class="literal">
JSON_TYPE()
</code>
</a>
</th>
<td>
Type of JSON value
</td>
<td>
</td>
</tr>
<tr>
<th scope="row">
<a class="link" href="json-modification-functions.html#function_json-unquote">
<code class="literal">
JSON_UNQUOTE()
</code>
</a>
</th>
<td>
Unquote JSON value
</td>
<td>
</td>
</tr>
<tr>
<th scope="row">
<a class="link" href="json-attribute-functions.html#function_json-valid">
<code class="literal">
JSON_VALID()
</code>
</a>
</th>
<td>
Whether JSON value is valid
</td>
<td>
</td>
</tr>
<tr>
<th scope="row">
<a class="link" href="json-search-functions.html#function_json-value">
<code class="literal">
JSON_VALUE()
</code>
</a>
</th>
<td>
Extract value from JSON document at location pointed to by path
provided; return this value as VARCHAR(512) or specified type
</td>
<td>
</td>
</tr>
<tr>
<th scope="row">
<a class="link" href="json-search-functions.html#operator_member-of">
<code class="literal">
MEMBER OF()
</code>
</a>
</th>
<td>
Returns true (1) if first operand matches any element of JSON
array passed as second operand, otherwise returns false (0)
</td>
<td>
</td>
</tr>
</tbody>
</table>
</div>
<div class="table-contents">
<table cellpadding="0" cellspacing="0" style="position: fixed; top: 0px; display: none; left: 401px; width: 739px;">
<thead>
<tr>
<th style="width: 258.891px;">
Name
</th>
<th style="width: 389.953px;">
Description
</th>
<th style="width: 89.1562px;">
Deprecated
</th>
</tr>
</thead>
</table>
</div>
</div>
<br class="table-break"/>
<p>
MySQL supports two aggregate JSON functions
<a class="link" href="aggregate-functions.html#function_json-arrayagg">
<code class="literal">
JSON_ARRAYAGG()
</code>
</a>
and
<a class="link" href="aggregate-functions.html#function_json-objectagg">
<code class="literal">
JSON_OBJECTAGG()
</code>
</a>
. See
<a class="xref" href="aggregate-functions-and-modifiers.html" title="14.19 Aggregate Functions">
Section 14.19, “Aggregate Functions”
</a>
, for
descriptions of these.
</p>
<p>
MySQL also supports
<span class="quote">
“
<span class="quote">
pretty-printing
</span>
”
</span>
of JSON values
in an easy-to-read format, using the
<a class="link" href="json-utility-functions.html#function_json-pretty">
<code class="literal">
JSON_PRETTY()
</code>
</a>
function. You can see
how much storage space a given JSON value takes up, and how much
space remains for additional storage, using
<a class="link" href="json-utility-functions.html#function_json-storage-size">
<code class="literal">
JSON_STORAGE_SIZE()
</code>
</a>
and
<a class="link" href="json-utility-functions.html#function_json-storage-free">
<code class="literal">
JSON_STORAGE_FREE()
</code>
</a>
, respectively.
For complete descriptions of these functions, see
<a class="xref" href="json-utility-functions.html" title="14.17.8 JSON Utility Functions">
Section 14.17.8, “JSON Utility Functions”
</a>
.
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/mysql-shell-tutorial-python-table-insert.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="mysql-shell-tutorial-python-table-insert">
</a>
22.4.4.1 Insert Records into Tables
</h4>
</div>
</div>
</div>
<a class="indexterm" name="idm46045126899568">
</a>
<p>
You can use the
<code class="literal">
insert()
</code>
method with the
<code class="literal">
values()
</code>
method to insert records into an
existing relational table. The
<code class="literal">
insert()
</code>
method accepts individual columns or all columns in the table.
Use one or more
<code class="literal">
values()
</code>
methods to specify
the values to be inserted.
</p>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h5 class="title">
<a name="mysql-shell-tutorial-python-insert-complete-record">
</a>
Insert a Complete Record
</h5>
</div>
</div>
</div>
<a class="indexterm" name="idm46045126893376">
</a>
<p>
To insert a complete record, pass to the
<code class="literal">
insert()
</code>
method all columns in the table.
Then pass to the
<code class="literal">
values()
</code>
method one value
for each column. For example, to add a new record to the city
table in the
<code class="literal">
world_x
</code>
database, insert the
following record and press
<span class="keycap">
<strong>
Enter
</strong>
</span>
twice.
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-mysqlsh"><div class="docs-select-all right" id="sa32173326"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-mysqlsh"><span class="token prompt">mysql-py></span> db<span class="token punctuation">.</span>city<span class="token punctuation">.</span><span class="token function">insert</span><span class="token punctuation">(</span><span class="token string">"ID"</span><span class="token punctuation">,</span> <span class="token string">"Name"</span><span class="token punctuation">,</span> <span class="token string">"CountryCode"</span><span class="token punctuation">,</span> <span class="token string">"District"</span><span class="token punctuation">,</span> <span class="token string">"Info"</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">values</span><span class="token punctuation">(</span>
None<span class="token punctuation">,</span> <span class="token string">"Olympia"</span><span class="token punctuation">,</span> <span class="token string">"USA"</span><span class="token punctuation">,</span> <span class="token string">"Washington"</span><span class="token punctuation">,</span> <span class="token string">'{"Population": 5000}'</span><span class="token punctuation">)</span></code></pre>
</div>
<p>
The city table has five columns: ID, Name, CountryCode,
District, and Info. Each value must match the data type of the
column it represents.
</p>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h5 class="title">
<a name="mysql-shell-tutorial-python-insert-partial-record">
</a>
Insert a Partial Record
</h5>
</div>
</div>
</div>
<a class="indexterm" name="idm46045126884768">
</a>
<p>
The following example inserts values into the ID, Name, and
CountryCode columns of the city table.
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-mysqlsh"><div class="docs-select-all right" id="sa55574034"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-mysqlsh"><span class="token prompt">mysql-py></span> db<span class="token punctuation">.</span>city<span class="token punctuation">.</span><span class="token function">insert</span><span class="token punctuation">(</span><span class="token string">"ID"</span><span class="token punctuation">,</span> <span class="token string">"Name"</span><span class="token punctuation">,</span> <span class="token string">"CountryCode"</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">values</span><span class="token punctuation">(</span>
None<span class="token punctuation">,</span> <span class="token string">"Little Falls"</span><span class="token punctuation">,</span> <span class="token string">"USA"</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">values</span><span class="token punctuation">(</span>None<span class="token punctuation">,</span> <span class="token string">"Happy Valley"</span><span class="token punctuation">,</span> <span class="token string">"USA"</span><span class="token punctuation">)</span></code></pre>
</div>
<p>
When you specify columns using the
<code class="literal">
insert()
</code>
method, the number of values must match the number of columns.
In the previous example, you must supply three values to match
the three columns specified.
</p>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h5 class="title">
<a name="idm46045126879584">
</a>
Related Information
</h5>
</div>
</div>
</div>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
See
<a class="ulink" href="/doc/x-devapi-userguide/en/crud-ebnf-table-crud-functions.html#crud-ebnf-tableinsertfunction" target="_top">
TableInsertFunction
</a>
for
the full syntax definition.
</p>
</li>
</ul>
</div>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/mysql-cluster-programs-ndb-error-reporter.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="mysql-cluster-programs-ndb-error-reporter">
</a>
25.5.12 ndb_error_reporter — NDB Error-Reporting Utility
</h3>
</div>
</div>
</div>
<a class="indexterm" name="idm46045103152144">
</a>
<a class="indexterm" name="idm46045103151200">
</a>
<p>
<a class="link" href="mysql-cluster-programs-ndb-error-reporter.html" title="25.5.12 ndb_error_reporter — NDB Error-Reporting Utility">
<span class="command">
<strong>
ndb_error_reporter
</strong>
</span>
</a>
creates an archive from
data node and management node log files that can be used to help
diagnose bugs or other problems with a cluster.
<span class="emphasis">
<em>
It is
highly recommended that you make use of this utility when filing
reports of bugs in NDB Cluster
</em>
</span>
.
</p>
<p>
Options that can be used with
<a class="link" href="mysql-cluster-programs-ndb-error-reporter.html" title="25.5.12 ndb_error_reporter — NDB Error-Reporting Utility">
<span class="command">
<strong>
ndb_error_reporter
</strong>
</span>
</a>
are shown in the following
table. Additional descriptions follow the table.
</p>
<p>
</p>
<h4>
<a name="idm46045103144544">
</a>
Usage
</h4>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-terminal"><div class="docs-select-all right" id="sa58131355"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-terminal">ndb_error_reporter <em class="replaceable">path/to/config-file</em> <span class="token punctuation">[</span><em class="replaceable">username</em><span class="token punctuation">]</span> <span class="token punctuation">[</span><em class="replaceable">options</em><span class="token punctuation">]</span></code></pre>
</div>
<p>
This utility is intended for use on a management node host, and
requires the path to the management host configuration file
(usually named
<code class="filename">
config.ini
</code>
). Optionally, you
can supply the name of a user that is able to access the
cluster's data nodes using SSH, to copy the data node log files.
<a class="link" href="mysql-cluster-programs-ndb-error-reporter.html" title="25.5.12 ndb_error_reporter — NDB Error-Reporting Utility">
<span class="command">
<strong>
ndb_error_reporter
</strong>
</span>
</a>
then includes all of these
files in archive that is created in the same directory in which
it is run. The archive is named
<code class="filename">
ndb_error_report_
<em class="replaceable">
<code>
YYYYMMDDhhmmss
</code>
</em>
.tar.bz2
</code>
,
where
<em class="replaceable">
<code>
YYYYMMDDhhmmss
</code>
</em>
is a datetime
string.
</p>
<p>
<a class="indexterm" name="idm46045103136848">
</a>
<a class="link" href="mysql-cluster-programs-ndb-error-reporter.html" title="25.5.12 ndb_error_reporter — NDB Error-Reporting Utility">
<span class="command">
<strong>
ndb_error_reporter
</strong>
</span>
</a>
also accepts the options
listed here:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<a name="option_ndb_error_reporter_connection-timeout">
</a>
<a class="link" href="mysql-cluster-programs-ndb-error-reporter.html#option_ndb_error_reporter_connection-timeout">
<code class="option">
--connection-timeout=
<em class="replaceable">
<code>
timeout
</code>
</em>
</code>
</a>
</p>
<a class="indexterm" name="idm46045103131184">
</a>
<a class="indexterm" name="idm46045103129680">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for connection-timeout">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--connection-timeout=#
</code>
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Integer
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
0
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
Wait this many seconds when trying to connect to nodes
before timing out.
</p>
</li>
<li class="listitem">
<p>
<a name="option_ndb_error_reporter_dry-scp">
</a>
<a class="link" href="mysql-cluster-programs-ndb-error-reporter.html#option_ndb_error_reporter_dry-scp">
<code class="option">
--dry-scp
</code>
</a>
</p>
<a class="indexterm" name="idm46045103115456">
</a>
<a class="indexterm" name="idm46045103113968">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for dry-scp">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--dry-scp
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
Run
<a class="link" href="mysql-cluster-programs-ndb-error-reporter.html" title="25.5.12 ndb_error_reporter — NDB Error-Reporting Utility">
<span class="command">
<strong>
ndb_error_reporter
</strong>
</span>
</a>
without using scp
from remote hosts. Used for testing only.
</p>
</li>
<li class="listitem">
<p>
<a name="option_ndb_error_reporter_help">
</a>
<a class="link" href="mysql-cluster-programs-ndb-error-reporter.html#option_ndb_error_reporter_help">
<code class="option">
--help
</code>
</a>
</p>
<a class="indexterm" name="idm46045103102832">
</a>
<a class="indexterm" name="idm46045103101344">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for help">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--help
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
Display help text and exit.
</p>
</li>
<li class="listitem">
<p>
<a name="option_ndb_error_reporter_fs">
</a>
<a class="link" href="mysql-cluster-programs-ndb-error-reporter.html#option_ndb_error_reporter_fs">
<code class="option">
--fs
</code>
</a>
</p>
<a class="indexterm" name="idm46045103091664">
</a>
<a class="indexterm" name="idm46045103090176">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for fs">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--fs
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
Copy the data node file systems to the management host and
include them in the archive.
</p>
<p>
Because data node file systems can be extremely large, even
after being compressed, we ask that you please do
<span class="emphasis">
<em>
not
</em>
</span>
send archives created using this
option to Oracle unless you are specifically requested to do
so.
</p>
</li>
<li class="listitem">
<p>
<a name="option_ndb_error_reporter_skip-nodegroup">
</a>
<a class="link" href="mysql-cluster-programs-ndb-error-reporter.html#option_ndb_error_reporter_skip-nodegroup">
<code class="option">
--skip-nodegroup=
<em class="replaceable">
<code>
nodegroup_id
</code>
</em>
</code>
</a>
</p>
<a class="indexterm" name="idm46045103078848">
</a>
<a class="indexterm" name="idm46045103077360">
</a>
<div class="informaltable">
<table frame="box" rules="all" summary="Properties for connection-timeout">
<colgroup>
<col style="width: 30%"/>
<col style="width: 70%"/>
</colgroup>
<tbody>
<tr>
<th>
Command-Line Format
</th>
<td>
<code class="literal">
--connection-timeout=#
</code>
</td>
</tr>
<tr>
<th>
Type
</th>
<td>
Integer
</td>
</tr>
<tr>
<th>
Default Value
</th>
<td>
<code class="literal">
0
</code>
</td>
</tr>
</tbody>
</table>
</div>
<p>
Skip all nodes belong to the node group having the supplied
node group ID.
</p>
</li>
</ul>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/replication-solutions-diffengines.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="replication-solutions-diffengines">
</a>
19.4.4 Using Replication with Different Source and Replica Storage Engines
</h3>
</div>
</div>
</div>
<p>
It does not matter for the replication process whether the
original table on the source and the replicated table on the
replica use different storage engine types. In fact, the
<a class="link" href="server-system-variables.html#sysvar_default_storage_engine">
<code class="literal">
default_storage_engine
</code>
</a>
system
variable is not replicated.
</p>
<p>
This provides a number of benefits in the replication process in
that you can take advantage of different engine types for
different replication scenarios. For example, in a typical
scale-out scenario (see
<a class="xref" href="replication-solutions-scaleout.html" title="19.4.5 Using Replication for Scale-Out">
Section 19.4.5, “Using Replication for Scale-Out”
</a>
), you want to use
<code class="literal">
InnoDB
</code>
tables on the source to take advantage
of the transactional functionality, but use
<code class="literal">
MyISAM
</code>
on the replicas where transaction
support is not required because the data is only read. When using
replication in a data-logging environment you may want to use the
<code class="literal">
Archive
</code>
storage engine on the replica.
</p>
<p>
Configuring different engines on the source and replica depends on
how you set up the initial replication process:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
If you used
<a class="link" href="mysqldump.html" title="6.5.4 mysqldump — A Database Backup Program">
<span class="command">
<strong>
mysqldump
</strong>
</span>
</a>
to create the
database snapshot on your source, you could edit the dump file
text to change the engine type used on each table.
</p>
<p>
Another alternative for
<a class="link" href="mysqldump.html" title="6.5.4 mysqldump — A Database Backup Program">
<span class="command">
<strong>
mysqldump
</strong>
</span>
</a>
is to
disable engine types that you do not want to use on the
replica before using the dump to build the data on the
replica. For example, you can add the
<code class="option">
--skip-federated
</code>
option on your replica to
disable the
<a class="link" href="federated-storage-engine.html" title="18.8 The FEDERATED Storage Engine">
<code class="literal">
FEDERATED
</code>
</a>
engine. If
a specific engine does not exist for a table to be created,
MySQL uses the default engine type, usually
<a class="link" href="innodb-storage-engine.html" title="Chapter 17 The InnoDB Storage Engine">
<code class="literal">
InnoDB
</code>
</a>
. (This requires that the
<a class="link" href="sql-mode.html#sqlmode_no_engine_substitution">
<code class="literal">
NO_ENGINE_SUBSTITUTION
</code>
</a>
SQL
mode is not enabled.) If you want to disable additional
engines in this way, you may want to consider building a
special binary to be used on the replica that supports only
the engines you want.
</p>
</li>
<li class="listitem">
<p>
If you use raw data files (a binary backup) to set up the
replica, it is not possible to change the initial table
format. Instead, use
<a class="link" href="alter-table.html" title="15.1.9 ALTER TABLE Statement">
<code class="literal">
ALTER
TABLE
</code>
</a>
to change the table types after the replica
has been started.
</p>
</li>
<li class="listitem">
<p>
For new source/replica replication setups where there are
currently no tables on the source, avoid specifying the engine
type when creating new tables.
</p>
</li>
</ul>
</div>
<p>
If you are already running a replication solution and want to
convert your existing tables to another engine type, follow these
steps:
</p>
<div class="orderedlist">
<ol class="orderedlist" type="1">
<li class="listitem">
<p>
Stop the replica from running replication updates:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa62110754"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">STOP</span> <span class="token keyword">REPLICA</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
This makes it possible to change engine types without
interruption.
</p>
</li>
<li class="listitem">
<p>
Execute an
<code class="literal">
ALTER TABLE ...
ENGINE='
<em class="replaceable">
<code>
engine_type
</code>
</em>
'
</code>
for
each table to be changed.
</p>
</li>
<li class="listitem">
<p>
Start the replication process again:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa51004341"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">START</span> <span class="token keyword">REPLICA</span><span class="token punctuation">;</span></code></pre>
</div>
</li>
</ol>
</div>
<p>
Although the
<a class="link" href="server-system-variables.html#sysvar_default_storage_engine">
<code class="literal">
default_storage_engine
</code>
</a>
variable
is not replicated, be aware that
<a class="link" href="create-table.html" title="15.1.20 CREATE TABLE Statement">
<code class="literal">
CREATE
TABLE
</code>
</a>
and
<a class="link" href="alter-table.html" title="15.1.9 ALTER TABLE Statement">
<code class="literal">
ALTER TABLE
</code>
</a>
statements that include the engine specification are replicated to
the replica correctly. If, in the case of a
<a class="link" href="csv-storage-engine.html" title="18.4 The CSV Storage Engine">
<code class="literal">
CSV
</code>
</a>
table, you execute this
statement:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa13030485"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">ALTER</span> <span class="token keyword">TABLE</span> csvtable <span class="token keyword">ENGINE</span><span class="token operator">=</span><span class="token string">'MyISAM'</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
This statement is replicated; the table's engine type on the
replica is converted to
<code class="literal">
InnoDB
</code>
, even if you
have previously changed the table type on the replica to an engine
other than
<code class="literal">
CSV
</code>
. If you want to retain engine
differences on the source and replica, you should be careful to
use the
<a class="link" href="server-system-variables.html#sysvar_default_storage_engine">
<code class="literal">
default_storage_engine
</code>
</a>
variable on the source when creating a new table. For example,
instead of:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa1063653"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> tablea <span class="token punctuation">(</span>columna <span class="token datatype">int</span><span class="token punctuation">)</span> <span class="token keyword">Engine</span><span class="token operator">=</span>MyISAM<span class="token punctuation">;</span></code></pre>
</div>
<p>
Use this format:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa65213496"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SET</span> default_storage_engine<span class="token operator">=</span>MyISAM<span class="token punctuation">;</span>
<span class="token prompt">mysql></span> <span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> tablea <span class="token punctuation">(</span>columna <span class="token datatype">int</span><span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
When replicated, the
<a class="link" href="server-system-variables.html#sysvar_default_storage_engine">
<code class="literal">
default_storage_engine
</code>
</a>
variable
is ignored, and the
<a class="link" href="create-table.html" title="15.1.20 CREATE TABLE Statement">
<code class="literal">
CREATE TABLE
</code>
</a>
statement executes on the replica using the replica's default
engine.
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/partitioning-subpartitions.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="partitioning-subpartitions">
</a>
26.2.6 Subpartitioning
</h3>
</div>
</div>
</div>
<a class="indexterm" name="idm46045084166368">
</a>
<a class="indexterm" name="idm46045084165296">
</a>
<p>
Subpartitioning—also known as
<span class="firstterm">
composite
partitioning
</span>
—is the further division of each
partition in a partitioned table. Consider the following
<a class="link" href="create-table.html" title="15.1.20 CREATE TABLE Statement">
<code class="literal">
CREATE TABLE
</code>
</a>
statement:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa79876509"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> ts <span class="token punctuation">(</span>id <span class="token datatype">INT</span><span class="token punctuation">,</span> purchased <span class="token datatype">DATE</span><span class="token punctuation">)</span>
<span class="token keyword">PARTITION</span> <span class="token keyword">BY</span> <span class="token keyword">RANGE</span><span class="token punctuation">(</span> <span class="token function">YEAR</span><span class="token punctuation">(</span>purchased<span class="token punctuation">)</span> <span class="token punctuation">)</span>
<span class="token keyword">SUBPARTITION</span> <span class="token keyword">BY</span> <span class="token keyword">HASH</span><span class="token punctuation">(</span> <span class="token function">TO_DAYS</span><span class="token punctuation">(</span>purchased<span class="token punctuation">)</span> <span class="token punctuation">)</span>
<span class="token keyword">SUBPARTITIONS</span> <span class="token number">2</span> <span class="token punctuation">(</span>
<span class="token keyword">PARTITION</span> p0 <span class="token keyword">VALUES</span> <span class="token keyword">LESS</span> <span class="token keyword">THAN</span> <span class="token punctuation">(</span><span class="token number">1990</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
<span class="token keyword">PARTITION</span> p1 <span class="token keyword">VALUES</span> <span class="token keyword">LESS</span> <span class="token keyword">THAN</span> <span class="token punctuation">(</span><span class="token number">2000</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
<span class="token keyword">PARTITION</span> p2 <span class="token keyword">VALUES</span> <span class="token keyword">LESS</span> <span class="token keyword">THAN</span> <span class="token keyword">MAXVALUE</span>
<span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
Table
<code class="literal">
ts
</code>
has 3
<code class="literal">
RANGE
</code>
partitions. Each of these
partitions—
<code class="literal">
p0
</code>
,
<code class="literal">
p1
</code>
,
and
<code class="literal">
p2
</code>
—is further divided into 2
subpartitions. In effect, the entire table is divided into
<code class="literal">
3 * 2 = 6
</code>
partitions. However, due to the
action of the
<code class="literal">
PARTITION BY RANGE
</code>
clause, the
first 2 of these store only those records with a value less than
1990 in the
<code class="literal">
purchased
</code>
column.
</p>
<a class="indexterm" name="idm46045084154160">
</a>
<p>
It is possible to subpartition tables that are partitioned by
<code class="literal">
RANGE
</code>
or
<code class="literal">
LIST
</code>
.
Subpartitions may use either
<code class="literal">
HASH
</code>
or
<code class="literal">
KEY
</code>
partitioning. This is also known as
<span class="firstterm">
composite partitioning
</span>
.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
<code class="literal">
SUBPARTITION BY HASH
</code>
and
<code class="literal">
SUBPARTITION BY KEY
</code>
generally follow the
same syntax rules as
<code class="literal">
PARTITION BY HASH
</code>
and
<code class="literal">
PARTITION BY KEY
</code>
, respectively. An
exception to this is that
<code class="literal">
SUBPARTITION BY
KEY
</code>
(unlike
<code class="literal">
PARTITION BY KEY
</code>
)
does not currently support a default column, so the column
used for this purpose must be specified, even if the table has
an explicit primary key. This is a known issue which we are
working to address; see
<a class="xref" href="partitioning-limitations.html#partitioning-limitations-subpartitions" title="Issues with subpartitions">
Issues with subpartitions
</a>
, for
more information and an example.
</p>
</div>
<a class="indexterm" name="idm46045084142608">
</a>
<p>
It is also possible to define subpartitions explicitly using
<code class="literal">
SUBPARTITION
</code>
clauses to specify options for
individual subpartitions. For example, a more verbose fashion of
creating the same table
<code class="literal">
ts
</code>
as shown in the
previous example would be:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa27693517"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> ts <span class="token punctuation">(</span>id <span class="token datatype">INT</span><span class="token punctuation">,</span> purchased <span class="token datatype">DATE</span><span class="token punctuation">)</span>
<span class="token keyword">PARTITION</span> <span class="token keyword">BY</span> <span class="token keyword">RANGE</span><span class="token punctuation">(</span> <span class="token function">YEAR</span><span class="token punctuation">(</span>purchased<span class="token punctuation">)</span> <span class="token punctuation">)</span>
<span class="token keyword">SUBPARTITION</span> <span class="token keyword">BY</span> <span class="token keyword">HASH</span><span class="token punctuation">(</span> <span class="token function">TO_DAYS</span><span class="token punctuation">(</span>purchased<span class="token punctuation">)</span> <span class="token punctuation">)</span> <span class="token punctuation">(</span>
<span class="token keyword">PARTITION</span> p0 <span class="token keyword">VALUES</span> <span class="token keyword">LESS</span> <span class="token keyword">THAN</span> <span class="token punctuation">(</span><span class="token number">1990</span><span class="token punctuation">)</span> <span class="token punctuation">(</span>
<span class="token keyword">SUBPARTITION</span> s0<span class="token punctuation">,</span>
<span class="token keyword">SUBPARTITION</span> s1
<span class="token punctuation">)</span><span class="token punctuation">,</span>
<span class="token keyword">PARTITION</span> p1 <span class="token keyword">VALUES</span> <span class="token keyword">LESS</span> <span class="token keyword">THAN</span> <span class="token punctuation">(</span><span class="token number">2000</span><span class="token punctuation">)</span> <span class="token punctuation">(</span>
<span class="token keyword">SUBPARTITION</span> s2<span class="token punctuation">,</span>
<span class="token keyword">SUBPARTITION</span> s3
<span class="token punctuation">)</span><span class="token punctuation">,</span>
<span class="token keyword">PARTITION</span> p2 <span class="token keyword">VALUES</span> <span class="token keyword">LESS</span> <span class="token keyword">THAN</span> <span class="token keyword">MAXVALUE</span> <span class="token punctuation">(</span>
<span class="token keyword">SUBPARTITION</span> s4<span class="token punctuation">,</span>
<span class="token keyword">SUBPARTITION</span> s5
<span class="token punctuation">)</span>
<span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
Some syntactical items of note are listed here:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
Each partition must have the same number of subpartitions.
</p>
</li>
<li class="listitem">
<p>
If you explicitly define any subpartitions using
<code class="literal">
SUBPARTITION
</code>
on any partition of a
partitioned table, you must define them all. In other words,
the following statement fails:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa29172597"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> ts <span class="token punctuation">(</span>id <span class="token datatype">INT</span><span class="token punctuation">,</span> purchased <span class="token datatype">DATE</span><span class="token punctuation">)</span>
<span class="token keyword">PARTITION</span> <span class="token keyword">BY</span> <span class="token keyword">RANGE</span><span class="token punctuation">(</span> <span class="token function">YEAR</span><span class="token punctuation">(</span>purchased<span class="token punctuation">)</span> <span class="token punctuation">)</span>
<span class="token keyword">SUBPARTITION</span> <span class="token keyword">BY</span> <span class="token keyword">HASH</span><span class="token punctuation">(</span> <span class="token function">TO_DAYS</span><span class="token punctuation">(</span>purchased<span class="token punctuation">)</span> <span class="token punctuation">)</span> <span class="token punctuation">(</span>
<span class="token keyword">PARTITION</span> p0 <span class="token keyword">VALUES</span> <span class="token keyword">LESS</span> <span class="token keyword">THAN</span> <span class="token punctuation">(</span><span class="token number">1990</span><span class="token punctuation">)</span> <span class="token punctuation">(</span>
<span class="token keyword">SUBPARTITION</span> s0<span class="token punctuation">,</span>
<span class="token keyword">SUBPARTITION</span> s1
<span class="token punctuation">)</span><span class="token punctuation">,</span>
<span class="token keyword">PARTITION</span> p1 <span class="token keyword">VALUES</span> <span class="token keyword">LESS</span> <span class="token keyword">THAN</span> <span class="token punctuation">(</span><span class="token number">2000</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
<span class="token keyword">PARTITION</span> p2 <span class="token keyword">VALUES</span> <span class="token keyword">LESS</span> <span class="token keyword">THAN</span> <span class="token keyword">MAXVALUE</span> <span class="token punctuation">(</span>
<span class="token keyword">SUBPARTITION</span> s2<span class="token punctuation">,</span>
<span class="token keyword">SUBPARTITION</span> s3
<span class="token punctuation">)</span>
<span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
This statement would still fail even if it used
<code class="literal">
SUBPARTITIONS 2
</code>
.
</p>
</li>
<li class="listitem">
<p>
Each
<code class="literal">
SUBPARTITION
</code>
clause must include (at
a minimum) a name for the subpartition. Otherwise, you may
set any desired option for the subpartition or allow it to
assume its default setting for that option.
</p>
</li>
<li class="listitem">
<p>
Subpartition names must be unique across the entire table.
For example, the following
<a class="link" href="create-table.html" title="15.1.20 CREATE TABLE Statement">
<code class="literal">
CREATE
TABLE
</code>
</a>
statement is valid:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa61991008"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> ts <span class="token punctuation">(</span>id <span class="token datatype">INT</span><span class="token punctuation">,</span> purchased <span class="token datatype">DATE</span><span class="token punctuation">)</span>
<span class="token keyword">PARTITION</span> <span class="token keyword">BY</span> <span class="token keyword">RANGE</span><span class="token punctuation">(</span> <span class="token function">YEAR</span><span class="token punctuation">(</span>purchased<span class="token punctuation">)</span> <span class="token punctuation">)</span>
<span class="token keyword">SUBPARTITION</span> <span class="token keyword">BY</span> <span class="token keyword">HASH</span><span class="token punctuation">(</span> <span class="token function">TO_DAYS</span><span class="token punctuation">(</span>purchased<span class="token punctuation">)</span> <span class="token punctuation">)</span> <span class="token punctuation">(</span>
<span class="token keyword">PARTITION</span> p0 <span class="token keyword">VALUES</span> <span class="token keyword">LESS</span> <span class="token keyword">THAN</span> <span class="token punctuation">(</span><span class="token number">1990</span><span class="token punctuation">)</span> <span class="token punctuation">(</span>
<span class="token keyword">SUBPARTITION</span> s0<span class="token punctuation">,</span>
<span class="token keyword">SUBPARTITION</span> s1
<span class="token punctuation">)</span><span class="token punctuation">,</span>
<span class="token keyword">PARTITION</span> p1 <span class="token keyword">VALUES</span> <span class="token keyword">LESS</span> <span class="token keyword">THAN</span> <span class="token punctuation">(</span><span class="token number">2000</span><span class="token punctuation">)</span> <span class="token punctuation">(</span>
<span class="token keyword">SUBPARTITION</span> s2<span class="token punctuation">,</span>
<span class="token keyword">SUBPARTITION</span> s3
<span class="token punctuation">)</span><span class="token punctuation">,</span>
<span class="token keyword">PARTITION</span> p2 <span class="token keyword">VALUES</span> <span class="token keyword">LESS</span> <span class="token keyword">THAN</span> <span class="token keyword">MAXVALUE</span> <span class="token punctuation">(</span>
<span class="token keyword">SUBPARTITION</span> s4<span class="token punctuation">,</span>
<span class="token keyword">SUBPARTITION</span> s5
<span class="token punctuation">)</span>
<span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
</li>
</ul>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/group-replication-details.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="group-replication-details">
</a>
20.1.4 Group Replication Services
</h3>
</div>
</div>
</div>
<div class="toc">
<dl class="toc">
<dt>
<span class="section">
<a href="group-replication-group-membership.html">
20.1.4.1 Group Membership
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="group-replication-failure-detection.html">
20.1.4.2 Failure Detection
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="group-replication-fault-tolerance.html">
20.1.4.3 Fault-tolerance
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="group-replication-observability.html">
20.1.4.4 Observability
</a>
</span>
</dt>
</dl>
</div>
<a class="indexterm" name="idm46045134395360">
</a>
<p>
This section introduces some of the services that Group
Replication builds on.
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/information-schema-innodb-foreign-cols-table.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="information-schema-innodb-foreign-cols-table">
</a>
28.4.13 The INFORMATION_SCHEMA INNODB_FOREIGN_COLS Table
</h3>
</div>
</div>
</div>
<a class="indexterm" name="idm46045076998912">
</a>
<p>
The
<a class="link" href="information-schema-innodb-foreign-cols-table.html" title="28.4.13 The INFORMATION_SCHEMA INNODB_FOREIGN_COLS Table">
<code class="literal">
INNODB_FOREIGN_COLS
</code>
</a>
table
provides status information about
<code class="literal">
InnoDB
</code>
foreign key columns.
</p>
<p>
For related usage information and examples, see
<a class="xref" href="innodb-information-schema-system-tables.html" title="17.15.3 InnoDB INFORMATION_SCHEMA Schema Object Tables">
Section 17.15.3, “InnoDB INFORMATION_SCHEMA Schema Object Tables”
</a>
.
</p>
<p>
The
<a class="link" href="information-schema-innodb-foreign-cols-table.html" title="28.4.13 The INFORMATION_SCHEMA INNODB_FOREIGN_COLS Table">
<code class="literal">
INNODB_FOREIGN_COLS
</code>
</a>
table has
these columns:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<code class="literal">
ID
</code>
</p>
<p>
The foreign key index associated with this index key field;
the same value as
<code class="literal">
INNODB_FOREIGN.ID
</code>
.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
FOR_COL_NAME
</code>
</p>
<p>
The name of the associated column in the child table.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
REF_COL_NAME
</code>
</p>
<p>
The name of the associated column in the parent table.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
POS
</code>
</p>
<p>
The ordinal position of this key field within the foreign key
index, starting from 0.
</p>
</li>
</ul>
</div>
<h4>
<a name="idm46045076983136">
</a>
Example
</h4>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa9456526"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> INFORMATION_SCHEMA<span class="token punctuation">.</span>INNODB_FOREIGN_COLS <span class="token keyword">WHERE</span> ID <span class="token operator">=</span> <span class="token string">'test/fk1'</span>\G
<span class="token output"><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span> 1. row <span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span>
ID<span class="token punctuation">:</span> test/fk1
FOR_COL_NAME<span class="token punctuation">:</span> parent_id
REF_COL_NAME<span class="token punctuation">:</span> id
POS<span class="token punctuation">:</span> 0</span></code></pre>
</div>
<h4>
<a name="idm46045076980608">
</a>
Notes
</h4>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
You must have the
<a class="link" href="privileges-provided.html#priv_process">
<code class="literal">
PROCESS
</code>
</a>
privilege to query this table.
</p>
</li>
<li class="listitem">
<p>
Use the
<code class="literal">
INFORMATION_SCHEMA
</code>
<a class="link" href="information-schema-columns-table.html" title="28.3.8 The INFORMATION_SCHEMA COLUMNS Table">
<code class="literal">
COLUMNS
</code>
</a>
table or the
<a class="link" href="show-columns.html" title="15.7.7.6 SHOW COLUMNS Statement">
<code class="literal">
SHOW COLUMNS
</code>
</a>
statement to view
additional information about the columns of this table,
including data types and default values.
</p>
</li>
</ul>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/group-replication-distributed-recovery.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="group-replication-distributed-recovery">
</a>
20.5.4 Distributed Recovery
</h3>
</div>
</div>
</div>
<div class="toc">
<dl class="toc">
<dt>
<span class="section">
<a href="group-replication-distributed-recovery-connections.html">
20.5.4.1 Connections for Distributed Recovery
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="group-replication-cloning.html">
20.5.4.2 Cloning for Distributed Recovery
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="group-replication-tuning-recovery.html">
20.5.4.3 Configuring Distributed Recovery
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="group-replication-distributed-recovery-fault.html">
20.5.4.4 Fault Tolerance for Distributed Recovery
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="group-replication-view-changes.html">
20.5.4.5 How Distributed Recovery Works
</a>
</span>
</dt>
</dl>
</div>
<a class="indexterm" name="idm46045133180272">
</a>
<p>
Whenever a member joins or rejoins a replication group, it must
catch up with the transactions that were applied by the group
members before it joined, or while it was away. This process is
called distributed recovery.
</p>
<p>
The joining member begins by checking the relay log for its
<code class="literal">
group_replication_applier
</code>
channel for any
transactions that it already received from the group but did not
yet apply. If the joining member was in the group previously, it
might find unapplied transactions from before it left, in which
case it applies these as a first step. A member that is new to the
group does not have anything to apply.
</p>
<p>
After this, the joining member connects to an online existing
member to carry out state transfer. The joining member transfers
all the transactions that took place in the group before it joined
or while it was away, which are provided by the existing member
(called the
<span class="emphasis">
<em>
donor
</em>
</span>
). Next, the joining member
applies the transactions that took place in the group while this
state transfer was in progress. When this process is complete, the
joining member has caught up with the remaining servers in the
group, and it begins to participate normally in the group.
</p>
<p>
Group Replication uses a combination of these methods for state
transfer during distributed recovery:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
A remote cloning operation using the clone plugin's
function. To enable this method of state transfer, you must
install the clone plugin on the group members and the
joining member. Group Replication automatically configures
the required clone plugin settings and manages the remote
cloning operation.
</p>
</li>
<li class="listitem">
<p>
Replicating from a donor's binary log and applying the
transactions on the joining member. This method uses a
standard asynchronous replication channel named
<code class="literal">
group_replication_recovery
</code>
that is
established between the donor and the joining member.
</p>
</li>
</ul>
</div>
<p>
</p>
<p>
Group Replication automatically selects the best combination of
these methods for state transfer after you issue
<a class="link" href="start-group-replication.html" title="15.4.3.1 START GROUP_REPLICATION Statement">
<code class="literal">
START GROUP_REPLICATION
</code>
</a>
on the
joining member. To do this, Group Replication checks which
existing members are suitable as donors, how many transactions the
joining member needs from a donor, and whether any required
transactions are no longer present in the binary log files on any
group member. If the transaction gap between the joining member
and a suitable donor is large, or if some required transactions
are not in any donor's binary log files, Group Replication begins
distributed recovery with a remote cloning operation. If there is
not a large transaction gap, or if the clone plugin is not
installed, Group Replication proceeds directly to state transfer
from a donor's binary log.
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
During a remote cloning operation, the existing data on the
joining member is removed, and replaced with a copy of the
donor's data. When the remote cloning operation is complete
and the joining member has restarted, state transfer from a
donor's binary log is carried out to get the transactions that
the group applied while the remote cloning operation was in
progress.
</p>
</li>
<li class="listitem">
<p>
During state transfer from a donor's binary log, the joining
member replicates and applies the required transactions from
the donor's binary log, applying the transactions as they are
received, up to the point where the binary log records that
the joining member joined the group (a view change event).
While this is in progress, the joining member buffers the new
transactions that the group applies. When state transfer from
the binary log is complete, the joining member applies the
buffered transactions.
</p>
</li>
</ul>
</div>
<p>
When the joining member is up to date with all the group's
transactions, it is declared online and can participate in the
group as a normal member, and distributed recovery is complete.
</p>
<div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Tip
</div>
<p>
State transfer from the binary log is Group Replication's base
mechanism for distributed recovery, and if the donors and
joining members in your replication group are not set up to
support cloning, this is the only available option. As state
transfer from the binary log is based on classic asynchronous
replication, it might take a very long time if the server
joining the group does not have the group's data at all, or has
data taken from a very old backup image. In this situation, it
is therefore recommended that before adding a server to the
group, you should set it up with the group's data by
transferring a fairly recent snapshot of a server already in the
group. This minimizes the time taken for distributed recovery,
and reduces the impact on donor servers, since they have to
retain and transfer fewer binary log files.
</p>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/ddl-rewriter-installation.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="ddl-rewriter-installation">
</a>
7.6.5.1 Installing or Uninstalling ddl_rewriter
</h4>
</div>
</div>
</div>
<a class="indexterm" name="idm46045256199952">
</a>
<a class="indexterm" name="idm46045256198464">
</a>
<p>
This section describes how to install or uninstall the
<code class="literal">
ddl_rewriter
</code>
plugin. For general information
about installing plugins, see
<a class="xref" href="plugin-loading.html" title="7.6.1 Installing and Uninstalling Plugins">
Section 7.6.1, “Installing and Uninstalling Plugins”
</a>
.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
If installed, the
<code class="literal">
ddl_rewriter
</code>
plugin
involves some minimal overhead even when disabled. To avoid
this overhead, install
<code class="literal">
ddl_rewriter
</code>
only
for the period during which you intend to use it.
</p>
<p>
The primary use case is modification of statements restored
from dump files, so the typical usage pattern is: 1) Install
the plugin; 2) restore the dump file or files; 3) uninstall
the plugin.
</p>
</div>
<p>
To be usable by the server, the plugin library file must be
located in the MySQL plugin directory (the directory named by
the
<a class="link" href="server-system-variables.html#sysvar_plugin_dir">
<code class="literal">
plugin_dir
</code>
</a>
system
variable). If necessary, configure the plugin directory location
by setting the value of
<a class="link" href="server-system-variables.html#sysvar_plugin_dir">
<code class="literal">
plugin_dir
</code>
</a>
at server startup.
</p>
<p>
The plugin library file base name is
<code class="literal">
ddl_rewriter
</code>
. The file name suffix differs
per platform (for example,
<code class="filename">
.so
</code>
for Unix and
Unix-like systems,
<code class="filename">
.dll
</code>
for Windows).
</p>
<p>
To install the
<code class="literal">
ddl_rewriter
</code>
plugin, use the
<a class="link" href="install-plugin.html" title="15.7.4.4 INSTALL PLUGIN Statement">
<code class="literal">
INSTALL PLUGIN
</code>
</a>
statement,
adjusting the
<code class="filename">
.so
</code>
suffix for your platform
as necessary:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa87064916"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">INSTALL</span> <span class="token keyword">PLUGIN</span> ddl_rewriter <span class="token keyword">SONAME</span> <span class="token string">'ddl_rewriter.so'</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
To verify plugin installation, examine the Information Schema
<a class="link" href="information-schema-plugins-table.html" title="28.3.22 The INFORMATION_SCHEMA PLUGINS Table">
<code class="literal">
PLUGINS
</code>
</a>
table or use the
<a class="link" href="show-plugins.html" title="15.7.7.27 SHOW PLUGINS Statement">
<code class="literal">
SHOW PLUGINS
</code>
</a>
statement (see
<a class="xref" href="obtaining-plugin-information.html" title="7.6.2 Obtaining Server Plugin Information">
Section 7.6.2, “Obtaining Server Plugin Information”
</a>
). For example:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa40504707"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> PLUGIN_NAME<span class="token punctuation">,</span> PLUGIN_STATUS<span class="token punctuation">,</span> PLUGIN_TYPE
<span class="token keyword">FROM</span> INFORMATION_SCHEMA<span class="token punctuation">.</span><span class="token keyword">PLUGINS</span>
<span class="token keyword">WHERE</span> PLUGIN_NAME <span class="token operator">LIKE</span> <span class="token string">'ddl%'</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> PLUGIN_NAME <span class="token punctuation">|</span> PLUGIN_STATUS <span class="token punctuation">|</span> PLUGIN_TYPE <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> ddl_rewriter <span class="token punctuation">|</span> ACTIVE <span class="token punctuation">|</span> AUDIT <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span></code></pre>
</div>
<p>
As the preceding result shows,
<code class="literal">
ddl_rewriter
</code>
is implemented as an audit plugin.
</p>
<p>
If the plugin fails to initialize, check the server error log
for diagnostic messages.
</p>
<p>
Once installed as just described,
<code class="literal">
ddl_rewriter
</code>
remains installed until
uninstalled. To remove it, use
<a class="link" href="uninstall-plugin.html" title="15.7.4.6 UNINSTALL PLUGIN Statement">
<code class="literal">
UNINSTALL
PLUGIN
</code>
</a>
:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa53160038"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">UNINSTALL</span> <span class="token keyword">PLUGIN</span> ddl_rewriter<span class="token punctuation">;</span></code></pre>
</div>
<p>
If
<code class="literal">
ddl_rewriter
</code>
is installed, you can use the
<a class="link" href="ddl-rewriter-options.html#option_mysqld_ddl-rewriter">
<code class="option">
--ddl-rewriter
</code>
</a>
option for
subsequent server startups to control
<code class="literal">
ddl_rewriter
</code>
plugin activation. For example,
to prevent the plugin from being enabled at runtime, use this
option:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-ini"><div class="docs-select-all right" id="sa84715393"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-ini"><span class="token selector">[mysqld]</span>
<span class="token constant">ddl-rewriter</span><span class="token attr-value"><span class="token punctuation">=</span>OFF</span></code></pre>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/sys-sys-get-config.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="sys-sys-get-config">
</a>
30.4.5.19 The sys_get_config() Function
</h4>
</div>
</div>
</div>
<a class="indexterm" name="idm46045060696528">
</a>
<a class="indexterm" name="idm46045060695056">
</a>
<p>
Given a configuration option name, returns the option value
from the
<a class="link" href="sys-sys-config.html" title="30.4.2.1 The sys_config Table">
<code class="literal">
sys_config
</code>
</a>
table, or
the provided default value (which may be
<code class="literal">
NULL
</code>
) if the option does not exist in the
table.
</p>
<p>
If
<a class="link" href="sys-sys-get-config.html" title="30.4.5.19 The sys_get_config() Function">
<code class="literal">
sys_get_config()
</code>
</a>
returns the
default value and that value is
<code class="literal">
NULL
</code>
, it is
expected that the caller is able to handle
<code class="literal">
NULL
</code>
for the given configuration option.
</p>
<p>
By convention, routines that call
<a class="link" href="sys-sys-get-config.html" title="30.4.5.19 The sys_get_config() Function">
<code class="literal">
sys_get_config()
</code>
</a>
first check
whether the corresponding user-defined variable exists and is
non-
<code class="literal">
NULL
</code>
. If so, the routine uses the
variable value without reading the
<a class="link" href="sys-sys-config.html" title="30.4.2.1 The sys_config Table">
<code class="literal">
sys_config
</code>
</a>
table. If the
variable does not exist or is
<code class="literal">
NULL
</code>
, the
routine reads the option value from the table and sets the
user-defined variable to that value. For more information
about the relationship between configuration options and their
corresponding user-defined variables, see
<a class="xref" href="sys-sys-config.html" title="30.4.2.1 The sys_config Table">
Section 30.4.2.1, “The sys_config Table”
</a>
.
</p>
<p>
If you want to check whether the configuration option has
already been set and, if not, use the return value of
<code class="literal">
sys_get_config()
</code>
, you can use
<code class="literal">
IFNULL(...)
</code>
(see example later). However,
this should not be done inside a loop (for example, for each
row in a result set) because for repeated calls where the
assignment is needed only in the first iteration, using
<code class="literal">
IFNULL(...)
</code>
is expected to be significantly
slower than using an
<code class="literal">
IF (...) THEN ... END
IF;
</code>
block (see example later).
</p>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h5 class="title">
<a name="sys-sys-get-config-parameters">
</a>
Parameters
</h5>
</div>
</div>
</div>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<code class="literal">
in_variable_name VARCHAR(128)
</code>
: The
name of the configuration option for which to return the
value.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
in_default_value VARCHAR(128)
</code>
: The
default value to return if the configuration option is
not found in the
<code class="literal">
sys_config
</code>
table.
</p>
</li>
</ul>
</div>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h5 class="title">
<a name="sys-sys-get-config-return-value">
</a>
Return Value
</h5>
</div>
</div>
</div>
<p>
A
<code class="literal">
VARCHAR(128)
</code>
value.
</p>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h5 class="title">
<a name="sys-sys-get-config-example">
</a>
Example
</h5>
</div>
</div>
</div>
<p>
Get a configuration value from the
<a class="link" href="sys-sys-config.html" title="30.4.2.1 The sys_config Table">
<code class="literal">
sys_config
</code>
</a>
table, falling back
to 128 as the default if the option is not present in the
table:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa21440983"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> sys<span class="token punctuation">.</span>sys_get_config<span class="token punctuation">(</span><span class="token string">'statement_truncate_len'</span><span class="token punctuation">,</span> <span class="token number">128</span><span class="token punctuation">)</span> <span class="token keyword">AS</span> <span class="token keyword">Value</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> Value <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> 64 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span></code></pre>
</div>
<p>
One-liner example: Check whether the option is already set;
if not, assign the
<code class="literal">
IFNULL(...)
</code>
result
(using the value from the
<a class="link" href="sys-sys-config.html" title="30.4.2.1 The sys_config Table">
<code class="literal">
sys_config
</code>
</a>
table):
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa27692445"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SET</span> <span class="token variable">@sys.statement_truncate_len</span> <span class="token operator">=</span>
<span class="token function">IFNULL</span><span class="token punctuation">(</span><span class="token variable">@sys.statement_truncate_len</span><span class="token punctuation">,</span>
sys<span class="token punctuation">.</span>sys_get_config<span class="token punctuation">(</span><span class="token string">'statement_truncate_len'</span><span class="token punctuation">,</span> <span class="token number">64</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
<code class="literal">
IF (...) THEN ... END IF;
</code>
block example:
Check whether the option is already set; if not, assign the
value from the
<a class="link" href="sys-sys-config.html" title="30.4.2.1 The sys_config Table">
<code class="literal">
sys_config
</code>
</a>
table:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa44803775"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token function">IF</span> <span class="token punctuation">(</span><span class="token variable">@sys.statement_truncate_len</span> <span class="token operator">IS</span> <span class="token boolean">NULL</span><span class="token punctuation">)</span> <span class="token keyword">THEN</span>
<span class="token keyword">SET</span> <span class="token variable">@sys.statement_truncate_len</span> <span class="token operator">=</span> sys<span class="token punctuation">.</span>sys_get_config<span class="token punctuation">(</span><span class="token string">'statement_truncate_len'</span><span class="token punctuation">,</span> <span class="token number">64</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">END</span> <span class="token keyword">IF</span><span class="token punctuation">;</span></code></pre>
</div>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/replication-rules-table-options.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="replication-rules-table-options">
</a>
19.2.5.2 Evaluation of Table-Level Replication Options
</h4>
</div>
</div>
</div>
<p>
The replica checks for and evaluates table options only if
either of the following two conditions is true:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
No matching database options were found.
</p>
</li>
<li class="listitem">
<p>
One or more database options were found, and were evaluated
to arrive at an
<span class="quote">
“
<span class="quote">
execute
</span>
”
</span>
condition according
to the rules described in the previous section (see
<a class="xref" href="replication-rules-db-options.html" title="19.2.5.1 Evaluation of Database-Level Replication and Binary Logging Options">
Section 19.2.5.1, “Evaluation of Database-Level Replication and Binary Logging Options”
</a>
).
</p>
</li>
</ul>
</div>
<p>
First, as a preliminary condition, the replica checks whether
statement-based replication is enabled. If so, and the statement
occurs within a stored function, the replica executes the
statement and exits. If row-based replication is enabled, the
replica does not know whether a statement occurred within a
stored function on the source, so this condition does not apply.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
For statement-based replication, replication events represent
statements (all changes making up a given event are associated
with a single SQL statement); for row-based replication, each
event represents a change in a single table row (thus a single
statement such as
<code class="literal">
UPDATE mytable SET mycol =
1
</code>
may yield many row-based events). When viewed in
terms of events, the process of checking table options is the
same for both row-based and statement-based replication.
</p>
</div>
<p>
Having reached this point, if there are no table options, the
replica simply executes all events. If there are any
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-do-table">
<code class="option">
--replicate-do-table
</code>
</a>
or
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-wild-do-table">
<code class="option">
--replicate-wild-do-table
</code>
</a>
options, the event must match one of these if it is to be
executed; otherwise, it is ignored. If there are any
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-ignore-table">
<code class="option">
--replicate-ignore-table
</code>
</a>
or
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-wild-ignore-table">
<code class="option">
--replicate-wild-ignore-table
</code>
</a>
options, all events are executed except those that match any of
these options.
</p>
<div class="important" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Important
</div>
<p>
Table-level replication filters are only applied to tables
that are explicitly mentioned and operated on in the query.
They do not apply to tables that are implicitly updated by the
query. For example, a
<a class="link" href="grant.html" title="15.7.1.6 GRANT Statement">
<code class="literal">
GRANT
</code>
</a>
statement, which updates the
<code class="literal">
mysql.user
</code>
system table but does not mention that table, is not affected
by a filter that specifies
<code class="literal">
mysql.%
</code>
as the
wildcard pattern.
</p>
</div>
<p>
The following steps describe this evaluation in more detail. The
starting point is the end of the evaluation of the
database-level options, as described in
<a class="xref" href="replication-rules-db-options.html" title="19.2.5.1 Evaluation of Database-Level Replication and Binary Logging Options">
Section 19.2.5.1, “Evaluation of Database-Level Replication and Binary Logging Options”
</a>
.
</p>
<div class="orderedlist">
<ol class="orderedlist" type="1">
<li class="listitem">
<p>
Are there any table replication options?
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<b>
Yes.
</b>
Continue to step 2.
</p>
</li>
<li class="listitem">
<p>
<b>
No.
</b>
Execute the update and exit.
</p>
</li>
</ul>
</div>
</li>
<li class="listitem">
<p>
Which logging format is used?
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<b>
STATEMENT.
</b>
Carry out the remaining steps for each statement that
performs an update.
</p>
</li>
<li class="listitem">
<p>
<b>
ROW.
</b>
Carry out the remaining steps for each update of a
table row.
</p>
</li>
</ul>
</div>
</li>
<li class="listitem">
<p>
Are there any
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-do-table">
<code class="option">
--replicate-do-table
</code>
</a>
options?
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<b>
Yes.
</b>
Does the table match any of them?
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<p>
<b>
Yes.
</b>
Execute the update and exit.
</p>
</li>
<li class="listitem">
<p>
<b>
No.
</b>
Continue to step 4.
</p>
</li>
</ul>
</div>
</li>
<li class="listitem">
<p>
<b>
No.
</b>
Continue to step 4.
</p>
</li>
</ul>
</div>
</li>
<li class="listitem">
<p>
Are there any
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-ignore-table">
<code class="option">
--replicate-ignore-table
</code>
</a>
options?
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<b>
Yes.
</b>
Does the table match any of them?
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<p>
<b>
Yes.
</b>
Ignore the update and exit.
</p>
</li>
<li class="listitem">
<p>
<b>
No.
</b>
Continue to step 5.
</p>
</li>
</ul>
</div>
</li>
<li class="listitem">
<p>
<b>
No.
</b>
Continue to step 5.
</p>
</li>
</ul>
</div>
</li>
<li class="listitem">
<p>
Are there any
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-wild-do-table">
<code class="option">
--replicate-wild-do-table
</code>
</a>
options?
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<b>
Yes.
</b>
Does the table match any of them?
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<p>
<b>
Yes.
</b>
Execute the update and exit.
</p>
</li>
<li class="listitem">
<p>
<b>
No.
</b>
Continue to step 6.
</p>
</li>
</ul>
</div>
</li>
<li class="listitem">
<p>
<b>
No.
</b>
Continue to step 6.
</p>
</li>
</ul>
</div>
</li>
<li class="listitem">
<p>
Are there any
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-wild-ignore-table">
<code class="option">
--replicate-wild-ignore-table
</code>
</a>
options?
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<b>
Yes.
</b>
Does the table match any of them?
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<p>
<b>
Yes.
</b>
Ignore the update and exit.
</p>
</li>
<li class="listitem">
<p>
<b>
No.
</b>
Continue to step 7.
</p>
</li>
</ul>
</div>
</li>
<li class="listitem">
<p>
<b>
No.
</b>
Continue to step 7.
</p>
</li>
</ul>
</div>
</li>
<li class="listitem">
<p>
Is there another table to be tested?
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<b>
Yes.
</b>
Go back to step 3.
</p>
</li>
<li class="listitem">
<p>
<b>
No.
</b>
Continue to step 8.
</p>
</li>
</ul>
</div>
</li>
<li class="listitem">
<p>
Are there any
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-do-table">
<code class="option">
--replicate-do-table
</code>
</a>
or
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-wild-do-table">
<code class="option">
--replicate-wild-do-table
</code>
</a>
options?
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<b>
Yes.
</b>
Ignore the update and exit.
</p>
</li>
<li class="listitem">
<p>
<b>
No.
</b>
Execute the update and exit.
</p>
</li>
</ul>
</div>
</li>
</ol>
</div>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
Statement-based replication stops if a single SQL statement
operates on both a table that is included by a
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-do-table">
<code class="option">
--replicate-do-table
</code>
</a>
or
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-wild-do-table">
<code class="option">
--replicate-wild-do-table
</code>
</a>
option, and another table that is ignored by a
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-ignore-table">
<code class="option">
--replicate-ignore-table
</code>
</a>
or
<a class="link" href="replication-options-replica.html#option_mysqld_replicate-wild-ignore-table">
<code class="option">
--replicate-wild-ignore-table
</code>
</a>
option. The replica must either execute or ignore the complete
statement (which forms a replication event), and it cannot
logically do this. This also applies to row-based replication
for DDL statements, because DDL statements are always logged
as statements, without regard to the logging format in effect.
The only type of statement that can update both an included
and an ignored table and still be replicated successfully is a
DML statement that has been logged with
<a class="link" href="replication-options-binary-log.html#sysvar_binlog_format">
<code class="literal">
binlog_format=ROW
</code>
</a>
.
</p>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/delete-optimization.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="delete-optimization">
</a>
10.2.5.3 Optimizing DELETE Statements
</h4>
</div>
</div>
</div>
<a class="indexterm" name="idm46045227621216">
</a>
<p>
The time required to delete individual rows in a
<code class="literal">
MyISAM
</code>
table is exactly proportional to the
number of indexes. To delete rows more quickly, you can
increase the size of the key cache by increasing the
<a class="link" href="server-system-variables.html#sysvar_key_buffer_size">
<code class="literal">
key_buffer_size
</code>
</a>
system
variable. See
<a class="xref" href="server-configuration.html" title="7.1.1 Configuring the Server">
Section 7.1.1, “Configuring the Server”
</a>
.
</p>
<p>
To delete all rows from a
<code class="literal">
MyISAM
</code>
table,
<code class="literal">
TRUNCATE TABLE
<em class="replaceable">
<code>
tbl_name
</code>
</em>
</code>
is faster than
<code class="literal">
DELETE FROM
<em class="replaceable">
<code>
tbl_name
</code>
</em>
</code>
. Truncate
operations are not transaction-safe; an error occurs when
attempting one in the course of an active transaction or
active table lock. See
<a class="xref" href="truncate-table.html" title="15.1.37 TRUNCATE TABLE Statement">
Section 15.1.37, “TRUNCATE TABLE Statement”
</a>
.
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/calculating-days.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="calculating-days">
</a>
5.6.8 Calculating Visits Per Day
</h3>
</div>
</div>
</div>
<a class="indexterm" name="idm46045324604464">
</a>
<a class="indexterm" name="idm46045324603424">
</a>
<a class="indexterm" name="idm46045324602352">
</a>
<a class="indexterm" name="idm46045324601264">
</a>
<p>
The following example shows how you can use the bit group
functions to calculate the number of days per month a user has
visited a Web page.
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa19074488"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> t1 <span class="token punctuation">(</span><span class="token datatype">year</span> <span class="token datatype">YEAR</span><span class="token punctuation">,</span> <span class="token keyword">month</span> <span class="token datatype">INT</span> <span class="token keyword">UNSIGNED</span><span class="token punctuation">,</span>
<span class="token keyword">day</span> <span class="token datatype">INT</span> <span class="token keyword">UNSIGNED</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">INSERT</span> <span class="token keyword">INTO</span> t1 <span class="token keyword">VALUES</span><span class="token punctuation">(</span><span class="token number">2000</span><span class="token punctuation">,</span><span class="token number">1</span><span class="token punctuation">,</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">,</span><span class="token punctuation">(</span><span class="token number">2000</span><span class="token punctuation">,</span><span class="token number">1</span><span class="token punctuation">,</span><span class="token number">20</span><span class="token punctuation">)</span><span class="token punctuation">,</span><span class="token punctuation">(</span><span class="token number">2000</span><span class="token punctuation">,</span><span class="token number">1</span><span class="token punctuation">,</span><span class="token number">30</span><span class="token punctuation">)</span><span class="token punctuation">,</span><span class="token punctuation">(</span><span class="token number">2000</span><span class="token punctuation">,</span><span class="token number">2</span><span class="token punctuation">,</span><span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
<span class="token punctuation">(</span><span class="token number">2000</span><span class="token punctuation">,</span><span class="token number">2</span><span class="token punctuation">,</span><span class="token number">23</span><span class="token punctuation">)</span><span class="token punctuation">,</span><span class="token punctuation">(</span><span class="token number">2000</span><span class="token punctuation">,</span><span class="token number">2</span><span class="token punctuation">,</span><span class="token number">23</span><span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
The example table contains year-month-day values representing
visits by users to the page. To determine how many different
days in each month these visits occur, use this query:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa12472084"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">SELECT</span> <span class="token datatype">year</span><span class="token punctuation">,</span><span class="token keyword">month</span><span class="token punctuation">,</span><span class="token function">BIT_COUNT</span><span class="token punctuation">(</span><span class="token function">BIT_OR</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token operator"><<</span><span class="token keyword">day</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token keyword">AS</span> days <span class="token keyword">FROM</span> t1
<span class="token keyword">GROUP</span> <span class="token keyword">BY</span> <span class="token datatype">year</span><span class="token punctuation">,</span><span class="token keyword">month</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
Which returns:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-none"><div class="docs-select-all right" id="sa3768721"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-none">+------+-------+------+
| year | month | days |
+------+-------+------+
| 2000 | 1 | 3 |
| 2000 | 2 | 2 |
+------+-------+------+</code></pre>
</div>
<p>
The query calculates how many different days appear in the table
for each year/month combination, with automatic removal of
duplicate entries.
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/clone-plugin-monitoring.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="clone-plugin-monitoring">
</a>
7.6.7.10 Monitoring Cloning Operations
</h4>
</div>
</div>
</div>
<a class="indexterm" name="idm46045255312400">
</a>
<a class="indexterm" name="idm46045255310944">
</a>
<p>
This section describes options for monitoring cloning
operations.
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<a class="xref" href="clone-plugin-monitoring.html#clone-plugin-monitoring-performance-schema-clone-tables" title="Monitoring Cloning Operations using Performance Schema Clone Tables">
Monitoring Cloning Operations using Performance Schema Clone Tables
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="clone-plugin-monitoring.html#clone-plugin-monitoring-stage-events" title="Monitoring Cloning Operations Using Performance Schema Stage Events">
Monitoring Cloning Operations Using Performance Schema Stage Events
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="clone-plugin-monitoring.html#clone-plugin-performance-schema-instruments" title="Monitoring Cloning Operations Using Performance Schema Clone Instrumentation">
Monitoring Cloning Operations Using Performance Schema Clone
Instrumentation
</a>
</p>
</li>
<li class="listitem">
<p>
<a class="xref" href="clone-plugin-monitoring.html#clone-plugin-com-clone" title="The Com_clone Status Variable">
The Com_clone Status Variable
</a>
</p>
</li>
</ul>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h5 class="title">
<a name="clone-plugin-monitoring-performance-schema-clone-tables">
</a>
Monitoring Cloning Operations using Performance Schema Clone Tables
</h5>
</div>
</div>
</div>
<a class="indexterm" name="idm46045255303600">
</a>
<a class="indexterm" name="idm46045255302144">
</a>
<a class="indexterm" name="idm46045255300656">
</a>
<a class="indexterm" name="idm46045255299584">
</a>
<p>
A cloning operation may take some time to complete, depending
on the amount of data and other factors related to data
transfer. You can monitor the status and progress of a cloning
operation on the recipient MySQL server instance using the
<a class="link" href="performance-schema-clone-status-table.html" title="29.12.19.1 The clone_status Table">
<code class="literal">
clone_status
</code>
</a>
and
<a class="link" href="performance-schema-clone-progress-table.html" title="29.12.19.2 The clone_progress Table">
<code class="literal">
clone_progress
</code>
</a>
Performance Schema
tables.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
The
<a class="link" href="performance-schema-clone-status-table.html" title="29.12.19.1 The clone_status Table">
<code class="literal">
clone_status
</code>
</a>
and
<a class="link" href="performance-schema-clone-progress-table.html" title="29.12.19.2 The clone_progress Table">
<code class="literal">
clone_progress
</code>
</a>
Performance
Schema tables can be used to monitor a cloning operation on
the recipient MySQL server instance only. To monitor a
cloning operation on the donor MySQL server instance, use
the clone stage events, as described in
<a class="xref" href="clone-plugin-monitoring.html#clone-plugin-monitoring-stage-events" title="Monitoring Cloning Operations Using Performance Schema Stage Events">
Monitoring Cloning Operations Using Performance Schema Stage Events
</a>
.
</p>
</div>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
The
<a class="link" href="performance-schema-clone-status-table.html" title="29.12.19.1 The clone_status Table">
<code class="literal">
clone_status
</code>
</a>
table
provides the state of the current or last executed cloning
operation. A clone operation has four possible states:
<code class="literal">
Not Started
</code>
,
<code class="literal">
In
Progress
</code>
,
<code class="literal">
Completed
</code>
, and
<code class="literal">
Failed
</code>
.
</p>
</li>
<li class="listitem">
<p>
The
<a class="link" href="performance-schema-clone-progress-table.html" title="29.12.19.2 The clone_progress Table">
<code class="literal">
clone_progress
</code>
</a>
table
provides progress information for the current or last
executed clone operation, by stage. The stages of a
cloning operation include
<code class="literal">
DROP DATA
</code>
,
<code class="literal">
FILE COPY
</code>
,
<code class="literal">
PAGE_COPY
</code>
,
<code class="literal">
REDO_COPY
</code>
,
<code class="literal">
FILE_SYNC
</code>
,
<code class="literal">
RESTART
</code>
,
and
<code class="literal">
RECOVERY
</code>
.
</p>
</li>
</ul>
</div>
<p>
The
<a class="link" href="privileges-provided.html#priv_select">
<code class="literal">
SELECT
</code>
</a>
and
<a class="link" href="privileges-provided.html#priv_execute">
<code class="literal">
EXECUTE
</code>
</a>
privileges on the
Performance Schema is required to access the Performance
Schema clone tables.
</p>
<p>
To check the state of a cloning operation:
</p>
<div class="orderedlist">
<ol class="orderedlist" type="1">
<li class="listitem">
<p>
Connect to the recipient MySQL server instance.
</p>
</li>
<li class="listitem">
<p>
Query the
<a class="link" href="performance-schema-clone-status-table.html" title="29.12.19.1 The clone_status Table">
<code class="literal">
clone_status
</code>
</a>
table:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa92897283"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> STATE <span class="token keyword">FROM</span> performance_schema<span class="token punctuation">.</span>clone_status<span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> STATE <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> Completed <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span></code></pre>
</div>
</li>
</ol>
</div>
<p>
Should a failure occur during a cloning operation, you can
query the
<a class="link" href="performance-schema-clone-status-table.html" title="29.12.19.1 The clone_status Table">
<code class="literal">
clone_status
</code>
</a>
table for
error information:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa76272339"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> STATE<span class="token punctuation">,</span> ERROR_NO<span class="token punctuation">,</span> ERROR_MESSAGE <span class="token keyword">FROM</span> performance_schema<span class="token punctuation">.</span>clone_status<span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> STATE <span class="token punctuation">|</span> ERROR_NO <span class="token punctuation">|</span> ERROR_MESSAGE <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> Failed <span class="token punctuation">|</span> xxx <span class="token punctuation">|</span> "xxxxxxxxxxx" <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span></code></pre>
</div>
<p>
To review the details of each stage of a cloning operation:
</p>
<div class="orderedlist">
<ol class="orderedlist" type="1">
<li class="listitem">
<p>
Connect to the recipient MySQL server instance.
</p>
</li>
<li class="listitem">
<p>
Query the
<a class="link" href="performance-schema-clone-progress-table.html" title="29.12.19.2 The clone_progress Table">
<code class="literal">
clone_progress
</code>
</a>
table. For example, the following query provides state and
end time data for each stage of the cloning operation:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa89118896"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> STAGE<span class="token punctuation">,</span> STATE<span class="token punctuation">,</span> END_TIME <span class="token keyword">FROM</span> performance_schema<span class="token punctuation">.</span>clone_progress<span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> stage <span class="token punctuation">|</span> state <span class="token punctuation">|</span> end_time <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> DROP DATA <span class="token punctuation">|</span> Completed <span class="token punctuation">|</span> 2019<span class="token punctuation">-</span>01<span class="token punctuation">-</span>27 22:45:43.141261 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> FILE COPY <span class="token punctuation">|</span> Completed <span class="token punctuation">|</span> 2019<span class="token punctuation">-</span>01<span class="token punctuation">-</span>27 22:45:44.457572 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> PAGE COPY <span class="token punctuation">|</span> Completed <span class="token punctuation">|</span> 2019<span class="token punctuation">-</span>01<span class="token punctuation">-</span>27 22:45:44.577330 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> REDO COPY <span class="token punctuation">|</span> Completed <span class="token punctuation">|</span> 2019<span class="token punctuation">-</span>01<span class="token punctuation">-</span>27 22:45:44.679570 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> FILE SYNC <span class="token punctuation">|</span> Completed <span class="token punctuation">|</span> 2019<span class="token punctuation">-</span>01<span class="token punctuation">-</span>27 22:45:44.918547 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> RESTART <span class="token punctuation">|</span> Completed <span class="token punctuation">|</span> 2019<span class="token punctuation">-</span>01<span class="token punctuation">-</span>27 22:45:48.583565 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> RECOVERY <span class="token punctuation">|</span> Completed <span class="token punctuation">|</span> 2019<span class="token punctuation">-</span>01<span class="token punctuation">-</span>27 22:45:49.626595 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span></code></pre>
</div>
<p>
For other clone status and progress data points that you
can monitor, refer to
<a class="xref" href="performance-schema-clone-tables.html" title="29.12.19 Performance Schema Clone Tables">
Section 29.12.19, “Performance Schema Clone Tables”
</a>
.
</p>
</li>
</ol>
</div>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h5 class="title">
<a name="clone-plugin-monitoring-stage-events">
</a>
Monitoring Cloning Operations Using Performance Schema Stage Events
</h5>
</div>
</div>
</div>
<a class="indexterm" name="idm46045255256000">
</a>
<p>
A cloning operation may take some time to complete, depending
on the amount of data and other factors related to data
transfer. There are three stage events for monitoring the
progress of a cloning operation. Each stage event reports
<code class="literal">
<code class="literal">
WORK_COMPLETED
</code>
</code>
and
<code class="literal">
<code class="literal">
WORK_ESTIMATED
</code>
</code>
values.
Reported values are revised as the operation progresses.
</p>
<p>
This method of monitoring a cloning operation can be used on
the donor or recipient MySQL server instance.
</p>
<p>
In order of occurrence, cloning operation stage events
include:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<code class="literal">
stage/innodb/clone (file copy)
</code>
:
Indicates progress of the file copy phase of the cloning
operation.
<code class="literal">
<code class="literal">
WORK_ESTIMATED
</code>
</code>
and
<code class="literal">
<code class="literal">
WORK_COMPLETED
</code>
</code>
units
are file chunks. The number of files to be transferred is
known at the start of the file copy phase, and the number
of chunks is estimated based on the number of files.
<code class="literal">
WORK_ESTIMATED
</code>
is set to the number of
estimated file chunks.
<code class="literal">
WORK_COMPLETED
</code>
is updated after each chunk is sent.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
stage/innodb/clone (page copy)
</code>
:
Indicates progress of the page copy phase of cloning
operation.
<code class="literal">
WORK_ESTIMATED
</code>
and
<code class="literal">
WORK_COMPLETED
</code>
units are pages. Once
the file copy phase is completed, the number of pages to
be transferred is known, and
<code class="literal">
WORK_ESTIMATED
</code>
is set to this value.
<code class="literal">
WORK_COMPLETED
</code>
is updated after each
page is sent.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
stage/innodb/clone (redo copy)
</code>
:
Indicates progress of the redo copy phase of cloning
operation.
<code class="literal">
WORK_ESTIMATED
</code>
and
<code class="literal">
WORK_COMPLETED
</code>
units are redo chunks.
Once the page copy phase is completed, the number of redo
chunks to be transferred is known, and
<code class="literal">
WORK_ESTIMATED
</code>
is set to this value.
<code class="literal">
WORK_COMPLETED
</code>
is updated after each
chunk is sent.
</p>
</li>
</ul>
</div>
<p>
The following example demonstrates how to enable
<code class="literal">
stage/innodb/clone%
</code>
event instruments and
related consumer tables to monitor a cloning operation. For
information about Performance Schema stage event instruments
and related consumers, see
<a class="xref" href="performance-schema-stage-tables.html" title="29.12.5 Performance Schema Stage Event Tables">
Section 29.12.5, “Performance Schema Stage Event Tables”
</a>
.
</p>
<div class="orderedlist">
<ol class="orderedlist" type="1">
<li class="listitem">
<p>
Enable the
<code class="literal">
stage/innodb/clone%
</code>
instruments:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa66612239"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">UPDATE</span> performance_schema<span class="token punctuation">.</span>setup_instruments <span class="token keyword">SET</span> ENABLED <span class="token operator">=</span> <span class="token string">'YES'</span>
<span class="token keyword">WHERE</span> <span class="token keyword">NAME</span> <span class="token operator">LIKE</span> <span class="token string">'stage/innodb/clone%'</span><span class="token punctuation">;</span></code></pre>
</div>
</li>
<li class="listitem">
<p>
Enable the stage event consumer tables, which include
<a class="link" href="performance-schema-events-stages-current-table.html" title="29.12.5.1 The events_stages_current Table">
<code class="literal">
events_stages_current
</code>
</a>
,
<a class="link" href="performance-schema-events-stages-history-table.html" title="29.12.5.2 The events_stages_history Table">
<code class="literal">
events_stages_history
</code>
</a>
, and
<a class="link" href="performance-schema-events-stages-history-long-table.html" title="29.12.5.3 The events_stages_history_long Table">
<code class="literal">
events_stages_history_long
</code>
</a>
.
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa79998953"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">UPDATE</span> performance_schema<span class="token punctuation">.</span>setup_consumers <span class="token keyword">SET</span> ENABLED <span class="token operator">=</span> <span class="token string">'YES'</span>
<span class="token keyword">WHERE</span> <span class="token keyword">NAME</span> <span class="token operator">LIKE</span> <span class="token string">'%stages%'</span><span class="token punctuation">;</span></code></pre>
</div>
</li>
<li class="listitem">
<p>
Run a cloning operation. In this example, a local data
directory is cloned to a directory named
<code class="literal">
cloned_dir
</code>
.
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa57524014"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">CLONE</span> <span class="token keyword">LOCAL</span> <span class="token keyword">DATA</span> <span class="token keyword">DIRECTORY</span> <span class="token operator">=</span> <span class="token string">'/path/to/cloned_dir'</span><span class="token punctuation">;</span></code></pre>
</div>
</li>
<li class="listitem">
<p>
Check the progress of the cloning operation by querying
the Performance Schema
<a class="link" href="performance-schema-events-stages-current-table.html" title="29.12.5.1 The events_stages_current Table">
<code class="literal">
events_stages_current
</code>
</a>
table.
The stage event shown differs depending on the cloning
phase that is in progress. The
<code class="literal">
WORK_COMPLETED
</code>
column shows the work
completed. The
<code class="literal">
WORK_ESTIMATED
</code>
column
shows the work required in total.
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa50232779"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> EVENT_NAME<span class="token punctuation">,</span> WORK_COMPLETED<span class="token punctuation">,</span> WORK_ESTIMATED <span class="token keyword">FROM</span> performance_schema<span class="token punctuation">.</span>events_stages_current
<span class="token keyword">WHERE</span> EVENT_NAME <span class="token operator">LIKE</span> <span class="token string">'stage/innodb/clone%'</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> EVENT_NAME <span class="token punctuation">|</span> WORK_COMPLETED <span class="token punctuation">|</span> WORK_ESTIMATED <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> stage/innodb/clone (redo copy) <span class="token punctuation">|</span> 1 <span class="token punctuation">|</span> 1 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span></code></pre>
</div>
<p>
The
<a class="link" href="performance-schema-events-stages-current-table.html" title="29.12.5.1 The events_stages_current Table">
<code class="literal">
events_stages_current
</code>
</a>
table returns an empty set if the cloning operation has
finished. In this case, you can check the
<a class="link" href="performance-schema-events-stages-history-table.html" title="29.12.5.2 The events_stages_history Table">
<code class="literal">
events_stages_history
</code>
</a>
table
to view event data for the completed operation. For
example:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa3634943"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> EVENT_NAME<span class="token punctuation">,</span> WORK_COMPLETED<span class="token punctuation">,</span> WORK_ESTIMATED <span class="token keyword">FROM</span> events_stages_history
<span class="token keyword">WHERE</span> EVENT_NAME <span class="token operator">LIKE</span> <span class="token string">'stage/innodb/clone%'</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> EVENT_NAME <span class="token punctuation">|</span> WORK_COMPLETED <span class="token punctuation">|</span> WORK_ESTIMATED <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> stage/innodb/clone (file copy) <span class="token punctuation">|</span> 301 <span class="token punctuation">|</span> 301 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> stage/innodb/clone (page copy) <span class="token punctuation">|</span> 0 <span class="token punctuation">|</span> 0 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> stage/innodb/clone (redo copy) <span class="token punctuation">|</span> 1 <span class="token punctuation">|</span> 1 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span></code></pre>
</div>
</li>
</ol>
</div>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h5 class="title">
<a name="clone-plugin-performance-schema-instruments">
</a>
Monitoring Cloning Operations Using Performance Schema Clone
Instrumentation
</h5>
</div>
</div>
</div>
<a class="indexterm" name="idm46045255204320">
</a>
<p>
<a class="link" href="performance-schema.html" title="Chapter 29 MySQL Performance Schema">
Performance Schema
</a>
provides instrumentation for advanced performance monitoring
of clone operations. To view the available clone
instrumentation, and issue the following query:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa81823997"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">SELECT</span> <span class="token keyword">NAME</span><span class="token punctuation">,</span>ENABLED <span class="token keyword">FROM</span> performance_schema<span class="token punctuation">.</span>setup_instruments
<span class="token keyword">WHERE</span> <span class="token keyword">NAME</span> <span class="token operator">LIKE</span> <span class="token string">'%clone%'</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> NAME <span class="token punctuation">|</span> ENABLED <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> wait/synch/mutex/innodb/clone_snapshot_mutex <span class="token punctuation">|</span> NO <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> wait/synch/mutex/innodb/clone_sys_mutex <span class="token punctuation">|</span> NO <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> wait/synch/mutex/innodb/clone_task_mutex <span class="token punctuation">|</span> NO <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> wait/synch/mutex/group_rpl/LOCK_clone_donor_list <span class="token punctuation">|</span> NO <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> wait/synch/mutex/group_rpl/LOCK_clone_handler_run <span class="token punctuation">|</span> NO <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> wait/synch/mutex/group_rpl/LOCK_clone_query <span class="token punctuation">|</span> NO <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> wait/synch/mutex/group_rpl/LOCK_clone_read_mode <span class="token punctuation">|</span> NO <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> wait/synch/cond/group_rpl/COND_clone_handler_run <span class="token punctuation">|</span> NO <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> wait/io/file/innodb/innodb_clone_file <span class="token punctuation">|</span> YES <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> stage/innodb/clone (file copy) <span class="token punctuation">|</span> YES <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> stage/innodb/clone (redo copy) <span class="token punctuation">|</span> YES <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> stage/innodb/clone (page copy) <span class="token punctuation">|</span> YES <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> statement/abstract/clone <span class="token punctuation">|</span> YES <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> statement/clone/local <span class="token punctuation">|</span> YES <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> statement/clone/client <span class="token punctuation">|</span> YES <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> statement/clone/server <span class="token punctuation">|</span> YES <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> memory/innodb/clone <span class="token punctuation">|</span> YES <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">|</span> memory/clone/data <span class="token punctuation">|</span> YES <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span></code></pre>
</div>
<h6>
<a name="idm46045255197632">
</a>
Wait Instruments
</h6>
<p>
Performance schema wait instruments track events that take
time. Clone wait event instruments include:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<code class="literal">
wait/synch/mutex/innodb/clone_snapshot_mutex
</code>
:
Tracks wait events for the clone snapshot mutex, which
synchronizes access to the dynamic snapshot object (on the
donor and recipient) between multiple clone threads.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
wait/synch/mutex/innodb/clone_sys_mutex
</code>
:
Tracks wait events for the clone sys mutex. There is one
clone system object in a MySQL server instance. This mutex
synchronizes access to the clone system object on the
donor and recipient. It is acquired by clone threads and
other foreground and background threads.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
wait/synch/mutex/innodb/clone_task_mutex
</code>
:
Tracks wait events for the clone task mutex, used for
clone task management. The
<code class="literal">
clone_task_mutex
</code>
is acquired by clone
threads.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
wait/io/file/innodb/innodb_clone_file
</code>
:
Tracks all I/O wait operations for files that clone
operates on.
</p>
</li>
</ul>
</div>
<p>
For information about monitoring
<code class="literal">
InnoDB
</code>
mutex waits, see
<a class="xref" href="monitor-innodb-mutex-waits-performance-schema.html" title="17.16.2 Monitoring InnoDB Mutex Waits Using Performance Schema">
Section 17.16.2, “Monitoring InnoDB Mutex Waits Using Performance Schema”
</a>
.
For information about monitoring wait events in general, see
<a class="xref" href="performance-schema-wait-tables.html" title="29.12.4 Performance Schema Wait Event Tables">
Section 29.12.4, “Performance Schema Wait Event Tables”
</a>
.
</p>
<h6>
<a name="idm46045255185440">
</a>
Stage Instruments
</h6>
<p>
Performance Schema stage events track steps that occur during
the statement-execution process. Clone stage event instruments
include:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<code class="literal">
stage/innodb/clone (file copy)
</code>
:
Indicates progress of the file copy phase of the cloning
operation.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
stage/innodb/clone (redo copy)
</code>
:
Indicates progress of the redo copy phase of cloning
operation.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
stage/innodb/clone (page copy)
</code>
:
Indicates progress of the page copy phase of cloning
operation.
</p>
</li>
</ul>
</div>
<p>
For information about monitoring cloning operations using
stage events, see
<a class="xref" href="clone-plugin-monitoring.html#clone-plugin-monitoring-stage-events" title="Monitoring Cloning Operations Using Performance Schema Stage Events">
Monitoring Cloning Operations Using Performance Schema Stage Events
</a>
. For
general information about monitoring stage events, see
<a class="xref" href="performance-schema-stage-tables.html" title="29.12.5 Performance Schema Stage Event Tables">
Section 29.12.5, “Performance Schema Stage Event Tables”
</a>
.
</p>
<h6>
<a name="idm46045255177008">
</a>
Statement Instruments
</h6>
<p>
Performance Schema statement events track statement execution.
When a clone operation is initiated, the different statement
types tracked by clone statement instruments may be executed
in parallel. You can observe these statement events in the
Performance Schema statement event tables. The number of
statements that execute depends on the
<a class="link" href="clone-plugin-options-variables.html#sysvar_clone_max_concurrency">
<code class="literal">
clone_max_concurrency
</code>
</a>
and
<a class="link" href="clone-plugin-options-variables.html#sysvar_clone_autotune_concurrency">
<code class="literal">
clone_autotune_concurrency
</code>
</a>
settings.
</p>
<p>
Clone statement event instruments include:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<code class="literal">
statement/abstract/clone
</code>
: Tracks
statement events for any clone operation before it is
classified as a local, client, or server operation type.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
statement/clone/local
</code>
: Tracks clone
statement events for local clone operations; generated
when executing a
<a class="link" href="clone.html" title="15.7.5 CLONE Statement">
<code class="literal">
CLONE
LOCAL
</code>
</a>
statement.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
statement/clone/client
</code>
: Tracks remote
cloning statement events that occur on the recipient MySQL
server instance; generated when executing a
<a class="link" href="clone.html" title="15.7.5 CLONE Statement">
<code class="literal">
CLONE
INSTANCE
</code>
</a>
statement on the recipient.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
statement/clone/server
</code>
: Tracks remote
cloning statement events that occur on the donor MySQL
server instance; generated when executing a
<a class="link" href="clone.html" title="15.7.5 CLONE Statement">
<code class="literal">
CLONE
INSTANCE
</code>
</a>
statement on the recipient.
</p>
</li>
</ul>
</div>
<p>
For information about monitoring Performance Schema statement
events, see
<a class="xref" href="performance-schema-statement-tables.html" title="29.12.6 Performance Schema Statement Event Tables">
Section 29.12.6, “Performance Schema Statement Event Tables”
</a>
.
</p>
<h6>
<a name="idm46045255160368">
</a>
Memory Instruments
</h6>
<p>
Performance Schema memory instruments track memory usage.
Clone memory usage instruments include:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<code class="literal">
memory/innodb/clone
</code>
: Tracks memory
allocated by
<code class="literal">
InnoDB
</code>
for the dynamic
snapshot.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
memory/clone/data
</code>
: Tracks memory
allocated by the clone plugin during a clone operation.
</p>
</li>
</ul>
</div>
<p>
For information about monitoring memory usage using
Performance Schema, see
<a class="xref" href="performance-schema-memory-summary-tables.html" title="29.12.20.10 Memory Summary Tables">
Section 29.12.20.10, “Memory Summary Tables”
</a>
.
</p>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h5 class="title">
<a name="clone-plugin-com-clone">
</a>
The Com_clone Status Variable
</h5>
</div>
</div>
</div>
<a class="indexterm" name="idm46045255152448">
</a>
<p>
The
<code class="literal">
<a class="link" href="server-status-variables.html#statvar_Com_xxx">
Com_clone
</a>
</code>
status variable provides a count of
<a class="link" href="clone.html" title="15.7.5 CLONE Statement">
<code class="literal">
CLONE
</code>
</a>
statement executions.
</p>
<p>
For more information, refer to the discussion about
<code class="literal">
<a class="link" href="server-status-variables.html#statvar_Com_xxx">
Com_xxx
</a>
</code>
statement counter variables in
<a class="xref" href="server-status-variables.html" title="7.1.10 Server Status Variables">
Section 7.1.10, “Server Status Variables”
</a>
.
</p>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/sys-innodb-buffer-stats-by-schema.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="sys-innodb-buffer-stats-by-schema">
</a>
30.4.3.7 The innodb_buffer_stats_by_schema and x$innodb_buffer_stats_by_schema
Views
</h4>
</div>
</div>
</div>
<a class="indexterm" name="idm46045063195600">
</a>
<a class="indexterm" name="idm46045063194144">
</a>
<a class="indexterm" name="idm46045063192640">
</a>
<a class="indexterm" name="idm46045063191136">
</a>
<p>
These views summarize the information in the
<code class="literal">
INFORMATION_SCHEMA
</code>
<a class="link" href="information-schema-innodb-buffer-page-table.html" title="28.4.2 The INFORMATION_SCHEMA INNODB_BUFFER_PAGE Table">
<code class="literal">
INNODB_BUFFER_PAGE
</code>
</a>
table, grouped
by schema. By default, rows are sorted by descending buffer
size.
</p>
<div class="warning" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Warning
</div>
<p>
Querying views that access the
<a class="link" href="information-schema-innodb-buffer-page-table.html" title="28.4.2 The INFORMATION_SCHEMA INNODB_BUFFER_PAGE Table">
<code class="literal">
INNODB_BUFFER_PAGE
</code>
</a>
table can
affect performance. Do not query these views on a production
system unless you are aware of the performance impact and
have determined it to be acceptable. To avoid impacting
performance on a production system, reproduce the issue you
want to investigate and query buffer pool statistics on a
test instance.
</p>
</div>
<p>
The
<a class="link" href="sys-innodb-buffer-stats-by-schema.html" title="30.4.3.7 The innodb_buffer_stats_by_schema and x$innodb_buffer_stats_by_schema Views">
<code class="literal">
innodb_buffer_stats_by_schema
</code>
</a>
and
<a class="link" href="sys-innodb-buffer-stats-by-schema.html" title="30.4.3.7 The innodb_buffer_stats_by_schema and x$innodb_buffer_stats_by_schema Views">
<code class="literal">
x$innodb_buffer_stats_by_schema
</code>
</a>
views have these columns:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<code class="literal">
object_schema
</code>
</p>
<p>
The schema name for the object, or
<code class="literal">
InnoDB
System
</code>
if the table belongs to the
<code class="literal">
InnoDB
</code>
storage engine.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
allocated
</code>
</p>
<p>
The total number of bytes allocated for the schema.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
data
</code>
</p>
<p>
The total number of data bytes allocated for the schema.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
pages
</code>
</p>
<p>
The total number of pages allocated for the schema.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
pages_hashed
</code>
</p>
<p>
The total number of hashed pages allocated for the schema.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
pages_old
</code>
</p>
<p>
The total number of old pages allocated for the schema.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
rows_cached
</code>
</p>
<p>
The total number of cached rows for the schema.
</p>
</li>
</ul>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/selinux-context-mysqld-tcp-port.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="selinux-context-mysqld-tcp-port">
</a>
8.7.5.1 Setting the TCP Port Context for mysqld
</h4>
</div>
</div>
</div>
<a class="indexterm" name="idm46045231553456">
</a>
<p>
The default TCP port for
<a class="link" href="mysqld.html" title="6.3.1 mysqld — The MySQL Server">
<span class="command">
<strong>
mysqld
</strong>
</span>
</a>
is
<code class="literal">
3306
</code>
; and the SELinux context type used is
<code class="literal">
mysqld_port_t
</code>
.
</p>
<p>
If you configure
<a class="link" href="mysqld.html" title="6.3.1 mysqld — The MySQL Server">
<span class="command">
<strong>
mysqld
</strong>
</span>
</a>
to use a different
TCP
<a class="link" href="server-system-variables.html#sysvar_port">
<code class="literal">
port
</code>
</a>
, you may need to set
the context for the new port. For example to define the SELinux
context for a non-default port such as port 3307:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-terminal"><div class="docs-select-all right" id="sa9684063"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-terminal">semanage port <span class="token property">-a</span> <span class="token property">-t</span> mysqld_port_t <span class="token property">-p</span> tcp 3307</code></pre>
</div>
<p>
To confirm that the port is added:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-terminal"><div class="docs-select-all right" id="sa76196335"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-terminal"><span class="token prompt">$> </span><span class="token command">semanage</span> port <span class="token property">-l</span> | grep mysqld
mysqld_port_t tcp 3307<span class="token punctuation">,</span> 1186<span class="token punctuation">,</span> 3306<span class="token punctuation">,</span> 63132-63164</code></pre>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/mysql-cluster-limitations-syntax.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="mysql-cluster-limitations-syntax">
</a>
25.2.7.1 Noncompliance with SQL Syntax in NDB Cluster
</h4>
</div>
</div>
</div>
<a class="indexterm" name="idm46045123658896">
</a>
<p>
Some SQL statements relating to certain MySQL features produce
errors when used with
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDB
</code>
</a>
tables,
as described in the following list:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<b>
Temporary tables.
</b>
Temporary tables are not supported. Trying either to
create a temporary table that uses the
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDB
</code>
</a>
storage engine or to
alter an existing temporary table to use
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDB
</code>
</a>
fails with the error
<span class="errortext">
Table storage engine 'ndbcluster' does not
support the create option 'TEMPORARY'
</span>
.
</p>
</li>
<li class="listitem">
<p>
<b>
Indexes and keys in NDB tables.
</b>
Keys and indexes on NDB Cluster tables are subject to the
following limitations:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<p>
<b>
Column width.
</b>
Attempting to create an index on an
<code class="literal">
NDB
</code>
table column whose width is
greater than 3072 bytes is rejected with
<a class="ulink" href="/doc/mysql-errors/8.4/en/server-error-reference.html#error_er_too_long_key" target="_top">
<code class="literal">
ER_TOO_LONG_KEY
</code>
</a>
:
<span class="errortext">
Specified key was too long; max key length
is 3072 bytes
</span>
.
</p>
<p>
Attempting to create an index on an
<code class="literal">
NDB
</code>
table column whose width is
greater than 3056 bytes succeeds with a warning. In such
cases, statistical information is not generated, which
means a nonoptimal execution plan may be selected. For
this reason, you should consider making the index length
shorter than 3056 bytes if possible.
</p>
</li>
<li class="listitem">
<p>
<b>
TEXT and BLOB columns.
</b>
You cannot create indexes on
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDB
</code>
</a>
table columns that
use any of the
<a class="link" href="blob.html" title="13.3.4 The BLOB and TEXT Types">
<code class="literal">
TEXT
</code>
</a>
or
<a class="link" href="blob.html" title="13.3.4 The BLOB and TEXT Types">
<code class="literal">
BLOB
</code>
</a>
data types.
</p>
</li>
<li class="listitem">
<p>
<b>
FULLTEXT indexes.
</b>
The
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDB
</code>
</a>
storage engine
does not support
<code class="literal">
FULLTEXT
</code>
indexes,
which are possible for
<a class="link" href="myisam-storage-engine.html" title="18.2 The MyISAM Storage Engine">
<code class="literal">
MyISAM
</code>
</a>
and
<a class="link" href="innodb-storage-engine.html" title="Chapter 17 The InnoDB Storage Engine">
<code class="literal">
InnoDB
</code>
</a>
tables only.
</p>
<p>
However, you can create indexes on
<a class="link" href="char.html" title="13.3.2 The CHAR and VARCHAR Types">
<code class="literal">
VARCHAR
</code>
</a>
columns of
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDB
</code>
</a>
tables.
</p>
</li>
<li class="listitem">
<p>
<b>
USING HASH keys and NULL.
</b>
Using nullable columns in unique keys and primary keys
means that queries using these columns are handled as
full table scans. To work around this issue, make the
column
<code class="literal">
NOT NULL
</code>
, or re-create the
index without the
<code class="literal">
USING HASH
</code>
option.
</p>
</li>
<li class="listitem">
<p>
<b>
Prefixes.
</b>
There are no prefix indexes; only entire columns can
be indexed. (The size of an
<code class="literal">
NDB
</code>
column index is always the same as the width of the
column in bytes, up to and including 3072 bytes, as
described earlier in this section. Also see
<a class="xref" href="mysql-cluster-limitations-unsupported.html" title="25.2.7.6 Unsupported or Missing Features in NDB Cluster">
Section 25.2.7.6, “Unsupported or Missing Features in NDB Cluster”
</a>
,
for additional information.)
</p>
</li>
<li class="listitem">
<p>
<b>
BIT columns.
</b>
A
<a class="link" href="bit-type.html" title="13.1.5 Bit-Value Type - BIT">
<code class="literal">
BIT
</code>
</a>
column cannot be
a primary key, unique key, or index, nor can it be
part of a composite primary key, unique key, or index.
</p>
</li>
<li class="listitem">
<p>
<b>
AUTO_INCREMENT columns.
</b>
Like other MySQL storage engines, the
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDB
</code>
</a>
storage engine can
handle a maximum of one
<code class="literal">
AUTO_INCREMENT
</code>
column per table,
and this column must be indexed. However, in the case
of an NDB table with no explicit primary key, an
<code class="literal">
AUTO_INCREMENT
</code>
column is
automatically defined and used as a
<span class="quote">
“
<span class="quote">
hidden
</span>
”
</span>
primary key. For this reason,
you cannot create an
<code class="literal">
NDB
</code>
table
having an
<code class="literal">
AUTO_INCREMENT
</code>
column and
no explicit primary key.
</p>
<p>
The following
<a class="link" href="create-table.html" title="15.1.20 CREATE TABLE Statement">
<code class="literal">
CREATE
TABLE
</code>
</a>
statements do not work, as shown here:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa29204760"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token comment" spellcheck="true"># No index on AUTO_INCREMENT column; table has no primary key</span>
<span class="token comment" spellcheck="true"># Raises ER_WRONG_AUTO_KEY</span>
<span class="token prompt">mysql></span> <span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> n <span class="token punctuation">(</span>
<span class="token prompt"> -></span> a <span class="token datatype">INT</span><span class="token punctuation">,</span>
<span class="token prompt"> -></span> b <span class="token datatype">INT</span> <span class="token keyword">AUTO_INCREMENT</span>
<span class="token prompt"> -></span> <span class="token punctuation">)</span>
<span class="token prompt"> -></span> <span class="token keyword">ENGINE</span><span class="token operator">=</span><span class="token keyword">NDB</span><span class="token punctuation">;</span>
<span class="token output">ERROR 1075 (42000)<span class="token punctuation">:</span> Incorrect table definition; there can be only one auto
column and it must be defined as a key
# Index on AUTO_INCREMENT column; table has no primary key
# Raises NDB error 4335</span>
<span class="token prompt">mysql></span> <span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> n <span class="token punctuation">(</span>
<span class="token prompt"> -></span> a <span class="token datatype">INT</span><span class="token punctuation">,</span>
<span class="token prompt"> -></span> b <span class="token datatype">INT</span> <span class="token keyword">AUTO_INCREMENT</span><span class="token punctuation">,</span>
<span class="token prompt"> -></span> <span class="token keyword">KEY</span> k <span class="token punctuation">(</span>b<span class="token punctuation">)</span>
<span class="token prompt"> -></span> <span class="token punctuation">)</span>
<span class="token prompt"> -></span> <span class="token keyword">ENGINE</span><span class="token operator">=</span><span class="token keyword">NDB</span><span class="token punctuation">;</span>
<span class="token output">ERROR 1296 (HY000)<span class="token punctuation">:</span> Got error 4335 'Only one autoincrement column allowed per
table. Having a table without primary key uses an autoincr' from NDBCLUSTER</span></code></pre>
</div>
<p>
The following statement creates a table with a primary
key, an
<code class="literal">
AUTO_INCREMENT
</code>
column, and an
index on this column, and succeeds:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa8894644"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token comment" spellcheck="true"># Index on AUTO_INCREMENT column; table has a primary key</span>
<span class="token prompt">mysql></span> <span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> n <span class="token punctuation">(</span>
<span class="token prompt"> -></span> a <span class="token datatype">INT</span> <span class="token keyword">PRIMARY</span> <span class="token keyword">KEY</span><span class="token punctuation">,</span>
<span class="token prompt"> -></span> b <span class="token datatype">INT</span> <span class="token keyword">AUTO_INCREMENT</span><span class="token punctuation">,</span>
<span class="token prompt"> -></span> <span class="token keyword">KEY</span> k <span class="token punctuation">(</span>b<span class="token punctuation">)</span>
<span class="token prompt"> -></span> <span class="token punctuation">)</span>
<span class="token prompt"> -></span> <span class="token keyword">ENGINE</span><span class="token operator">=</span><span class="token keyword">NDB</span><span class="token punctuation">;</span>
<span class="token output">Query OK, 0 rows affected (0.38 sec)</span></code></pre>
</div>
</li>
</ul>
</div>
</li>
<li class="listitem">
<p>
<b>
Restrictions on foreign keys.
</b>
Support for foreign key constraints in NDB
8.4 is comparable to that provided by
<a class="link" href="innodb-storage-engine.html" title="Chapter 17 The InnoDB Storage Engine">
<code class="literal">
InnoDB
</code>
</a>
, subject to the
following restrictions:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<p>
Every column referenced as a foreign key requires an
explicit unique key, if it is not the table's
primary key.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
ON UPDATE CASCADE
</code>
is not supported
when the reference is to the parent table's primary
key.
</p>
<p>
This is because an update of a primary key is
implemented as a delete of the old row (containing the
old primary key) plus an insert of the new row (with a
new primary key). This is not visible to the
<code class="literal">
NDB
</code>
kernel, which views these two
rows as being the same, and thus has no way of knowing
that this update should be cascaded.
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
ON DELETE CASCADE
</code>
is also not
supported where the child table contains one or more
columns of any of the
<a class="link" href="blob.html" title="13.3.4 The BLOB and TEXT Types">
<code class="literal">
TEXT
</code>
</a>
or
<a class="link" href="blob.html" title="13.3.4 The BLOB and TEXT Types">
<code class="literal">
BLOB
</code>
</a>
types. (Bug #89511,
Bug #27484882)
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
SET DEFAULT
</code>
is not supported. (Also
not supported by
<a class="link" href="innodb-storage-engine.html" title="Chapter 17 The InnoDB Storage Engine">
<code class="literal">
InnoDB
</code>
</a>
.)
</p>
</li>
<li class="listitem">
<p>
The
<code class="literal">
NO ACTION
</code>
keyword is accepted but
treated as
<code class="literal">
RESTRICT
</code>
.
<code class="literal">
NO
ACTION
</code>
, which is a standard SQL keyword, is
the default in MySQL 8.4. (Also the same as
with
<code class="literal">
InnoDB
</code>
.)
</p>
</li>
<li class="listitem">
<p>
In earlier versions of NDB Cluster, when creating a
table with foreign key referencing an index in another
table, it sometimes appeared possible to create the
foreign key even if the order of the columns in the
indexes did not match, due to the fact that an
appropriate error was not always returned internally. A
partial fix for this issue improved the error used
internally to work in most cases; however, it remains
possible for this situation to occur in the event that
the parent index is a unique index. (Bug #18094360)
</p>
</li>
</ul>
</div>
<p>
For more information, see
<a class="xref" href="create-table-foreign-keys.html" title="15.1.20.5 FOREIGN KEY Constraints">
Section 15.1.20.5, “FOREIGN KEY Constraints”
</a>
, and
<a class="xref" href="constraint-foreign-key.html" title="1.7.3.2 FOREIGN KEY Constraints">
Section 1.7.3.2, “FOREIGN KEY Constraints”
</a>
.
</p>
</li>
<li class="listitem">
<p>
<b>
NDB Cluster and geometry data types.
</b>
<a class="indexterm" name="idm46045123575968">
</a>
Geometry data types (
<code class="literal">
WKT
</code>
and
<code class="literal">
WKB
</code>
) are supported for
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDB
</code>
</a>
tables. However, spatial
indexes are not supported.
</p>
</li>
<li class="listitem">
<p>
<b>
Character sets and binary log files.
</b>
Currently, the
<code class="literal">
ndb_apply_status
</code>
and
<code class="literal">
ndb_binlog_index
</code>
tables are created
using the
<code class="literal">
latin1
</code>
(ASCII) character set.
Because names of binary logs are recorded in this table,
binary log files named using non-Latin characters are not
referenced correctly in these tables. This is a known
issue, which we are working to fix. (Bug #50226)
</p>
<p>
To work around this problem, use only Latin-1 characters
when naming binary log files or setting any the
<a class="link" href="server-system-variables.html#sysvar_basedir">
<code class="option">
--basedir
</code>
</a>
,
<a class="link" href="replication-options-binary-log.html#option_mysqld_log-bin">
<code class="option">
--log-bin
</code>
</a>
, or
<a class="link" href="replication-options-binary-log.html#option_mysqld_log-bin-index">
<code class="option">
--log-bin-index
</code>
</a>
options.
</p>
</li>
<li class="listitem">
<p>
<b>
Creating NDB tables with user-defined partitioning.
</b>
<a class="indexterm" name="idm46045123562208">
</a>
<a class="indexterm" name="idm46045123560720">
</a>
<a class="indexterm" name="idm46045123559232">
</a>
Support for user-defined partitioning in NDB Cluster is
restricted to [
<code class="literal">
LINEAR
</code>
]
<code class="literal">
KEY
</code>
partitioning. Using any other
partitioning type with
<code class="literal">
ENGINE=NDB
</code>
or
<code class="literal">
ENGINE=NDBCLUSTER
</code>
in a
<a class="link" href="create-table.html" title="15.1.20 CREATE TABLE Statement">
<code class="literal">
CREATE TABLE
</code>
</a>
statement
results in an error.
</p>
<p>
It is possible to override this restriction, but doing so is
not supported for use in production settings. For details,
see
<a class="xref" href="partitioning-limitations-storage-engines.html#partitioning-limitations-ndb" title="User-defined partitioning and the NDB storage engine (NDB Cluster)">
User-defined partitioning and the NDB storage engine (NDB Cluster)
</a>
.
</p>
<p>
<b>
Default partitioning scheme.
</b>
All NDB Cluster tables are by default partitioned by
<code class="literal">
KEY
</code>
using the table's primary key
as the partitioning key. If no primary key is explicitly
set for the table, the
<span class="quote">
“
<span class="quote">
hidden
</span>
”
</span>
primary key
automatically created by the
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDB
</code>
</a>
storage engine is used
instead. For additional discussion of these and related
issues, see
<a class="xref" href="partitioning-key.html" title="26.2.5 KEY Partitioning">
Section 26.2.5, “KEY Partitioning”
</a>
.
</p>
<p>
<a class="link" href="create-table.html" title="15.1.20 CREATE TABLE Statement">
<code class="literal">
CREATE TABLE
</code>
</a>
and
<a class="link" href="alter-table.html" title="15.1.9 ALTER TABLE Statement">
<code class="literal">
ALTER TABLE
</code>
</a>
statements that
would cause a user-partitioned
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDBCLUSTER
</code>
</a>
table not to meet
either or both of the following two requirements are not
permitted, and fail with an error:
</p>
<div class="orderedlist">
<ol class="orderedlist" type="1">
<li class="listitem">
<p>
The table must have an explicit primary key.
</p>
</li>
<li class="listitem">
<p>
All columns listed in the table's partitioning
expression must be part of the primary key.
</p>
</li>
</ol>
</div>
<p>
<b>
Exception.
</b>
If a user-partitioned
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDBCLUSTER
</code>
</a>
table is created
using an empty column-list (that is, using
<code class="literal">
PARTITION BY [LINEAR] KEY()
</code>
), then no
explicit primary key is required.
</p>
<p>
<b>
Maximum number of partitions for NDBCLUSTER tables.
</b>
The maximum number of partitions that can defined for a
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDBCLUSTER
</code>
</a>
table when
employing user-defined partitioning is 8 per node group.
(See
<a class="xref" href="mysql-cluster-nodes-groups.html" title="25.2.2 NDB Cluster Nodes, Node Groups, Fragment Replicas, and Partitions">
Section 25.2.2, “NDB Cluster Nodes, Node Groups, Fragment Replicas, and Partitions”
</a>
, for
more information about NDB Cluster node groups.
</p>
<p>
<b>
DROP PARTITION not supported.
</b>
It is not possible to drop partitions from
<a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
<code class="literal">
NDB
</code>
</a>
tables using
<code class="literal">
ALTER TABLE ... DROP PARTITION
</code>
. The
other partitioning extensions to
<a class="link" href="alter-table.html" title="15.1.9 ALTER TABLE Statement">
<code class="literal">
ALTER
TABLE
</code>
</a>
—
<code class="literal">
ADD PARTITION
</code>
,
<code class="literal">
REORGANIZE PARTITION
</code>
, and
<code class="literal">
COALESCE PARTITION
</code>
—are supported
for NDB tables, but use copying and so are not optimized.
See
<a class="xref" href="partitioning-management-range-list.html" title="26.3.1 Management of RANGE and LIST Partitions">
Section 26.3.1, “Management of RANGE and LIST Partitions”
</a>
and
<a class="xref" href="alter-table.html" title="15.1.9 ALTER TABLE Statement">
Section 15.1.9, “ALTER TABLE Statement”
</a>
.
</p>
<p>
<b>
Partition selection.
</b>
Partition selection is not supported for
<code class="literal">
NDB
</code>
tables. See
<a class="xref" href="partitioning-selection.html" title="26.5 Partition Selection">
Section 26.5, “Partition Selection”
</a>
, for more
information.
</p>
</li>
<li class="listitem">
<p>
<b>
JSON data type.
</b>
The MySQL
<a class="link" href="json.html" title="13.5 The JSON Data Type">
<code class="literal">
JSON
</code>
</a>
data type is
supported for
<code class="literal">
NDB
</code>
tables in the
<a class="link" href="mysqld.html" title="6.3.1 mysqld — The MySQL Server">
<span class="command">
<strong>
mysqld
</strong>
</span>
</a>
supplied with NDB
8.4.
</p>
<a class="indexterm" name="idm46045123517856">
</a>
<p>
An
<code class="literal">
NDB
</code>
table can have a maximum of 3
<code class="literal">
JSON
</code>
columns.
</p>
<p>
The NDB API has no special provision for working with
<code class="literal">
JSON
</code>
data, which it views simply as
<code class="literal">
BLOB
</code>
data. Handling data as
<code class="literal">
JSON
</code>
must be performed by the
application.
</p>
</li>
</ul>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/temporary-table-problems.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="temporary-table-problems">
</a>
B.3.6.2 TEMPORARY Table Problems
</h4>
</div>
</div>
</div>
<a class="indexterm" name="idm46045053357808">
</a>
<p>
Temporary tables created with
<a class="link" href="create-table.html" title="15.1.20 CREATE TABLE Statement">
<code class="literal">
CREATE TEMPORARY
TABLE
</code>
</a>
have the following limitations:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<code class="literal">
TEMPORARY
</code>
tables are supported only by
the
<code class="literal">
InnoDB
</code>
,
<code class="literal">
MEMORY
</code>
,
<code class="literal">
MyISAM
</code>
, and
<code class="literal">
MERGE
</code>
storage engines.
</p>
</li>
<li class="listitem">
<p>
Temporary tables are not supported for NDB Cluster.
</p>
</li>
<li class="listitem">
<p>
The
<a class="link" href="show-tables.html" title="15.7.7.39 SHOW TABLES Statement">
<code class="literal">
SHOW TABLES
</code>
</a>
statement
does not list
<code class="literal">
TEMPORARY
</code>
tables.
</p>
</li>
<li class="listitem">
<p>
To rename
<code class="literal">
TEMPORARY
</code>
tables,
<code class="literal">
RENAME TABLE
</code>
does not work. Use
<a class="link" href="alter-table.html" title="15.1.9 ALTER TABLE Statement">
<code class="literal">
ALTER TABLE
</code>
</a>
instead:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa10208070"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">ALTER</span> <span class="token keyword">TABLE</span> old_name <span class="token keyword">RENAME</span> new_name<span class="token punctuation">;</span></code></pre>
</div>
</li>
<li class="listitem">
<p>
You cannot refer to a
<code class="literal">
TEMPORARY
</code>
table
more than once in the same query. For example, the
following does not work:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa84574502"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> temp_table <span class="token keyword">JOIN</span> temp_table <span class="token keyword">AS</span> t2<span class="token punctuation">;</span></code></pre>
</div>
<a class="indexterm" name="idm46045053339376">
</a>
<a class="indexterm" name="idm46045053337888">
</a>
<p>
The statement produces this error:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-none"><div class="docs-select-all right" id="sa26280767"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-none">ERROR 1137: Can't reopen table: 'temp_table'</code></pre>
</div>
<p>
You can work around this issue if your query permits use
of a common table expression (CTE) rather than a
<code class="literal">
TEMPORARY
</code>
table. For example, this
fails with the
<span class="errortext">
Can't reopen table
</span>
error:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa56639970"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TEMPORARY</span> <span class="token keyword">TABLE</span> t <span class="token keyword">SELECT</span> <span class="token number">1</span> <span class="token keyword">AS</span> col_a<span class="token punctuation">,</span> <span class="token number">2</span> <span class="token keyword">AS</span> col_b<span class="token punctuation">;</span>
<span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> t <span class="token keyword">AS</span> t1 <span class="token keyword">JOIN</span> t <span class="token keyword">AS</span> t2<span class="token punctuation">;</span></code></pre>
</div>
<p>
To avoid the error, use a
<a class="link" href="with.html" title="15.2.20 WITH (Common Table Expressions)">
<code class="literal">
WITH
</code>
</a>
clause that defines a
CTE, rather than the
<code class="literal">
TEMPORARY
</code>
table:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa58507375"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">WITH</span> cte <span class="token keyword">AS</span> <span class="token punctuation">(</span><span class="token keyword">SELECT</span> <span class="token number">1</span> <span class="token keyword">AS</span> col_a<span class="token punctuation">,</span> <span class="token number">2</span> <span class="token keyword">AS</span> col_b<span class="token punctuation">)</span>
<span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> cte <span class="token keyword">AS</span> t1 <span class="token keyword">JOIN</span> cte <span class="token keyword">AS</span> t2<span class="token punctuation">;</span></code></pre>
</div>
</li>
<li class="listitem">
<p>
The
<span class="errortext">
Can't reopen table
</span>
error also
occurs if you refer to a temporary table multiple times in
a stored function under different aliases, even if the
references occur in different statements within the
function. It may occur for temporary tables created
outside stored functions and referred to across multiple
calling and callee functions.
</p>
</li>
<li class="listitem">
<p>
If a
<code class="literal">
TEMPORARY
</code>
is created with the same
name as an existing non-
<code class="literal">
TEMPORARY
</code>
table, the non-
<code class="literal">
TEMPORARY
</code>
table is
hidden until the
<code class="literal">
TEMPORARY
</code>
table is
dropped, even if the tables use different storage engines.
</p>
</li>
<li class="listitem">
<p>
There are known issues in using temporary tables with
replication. See
<a class="xref" href="replication-features-temptables.html" title="19.5.1.31 Replication and Temporary Tables">
Section 19.5.1.31, “Replication and Temporary Tables”
</a>
, for
more information.
</p>
</li>
</ul>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/document-store.html | <div id="docs-body">
<div class="chapter">
<div class="titlepage">
<div>
<div>
<h1 class="title">
<a name="document-store">
</a>
Chapter 22 Using MySQL as a Document Store
</h1>
</div>
</div>
</div>
<div class="toc">
<p>
<b>
Table of Contents
</b>
</p>
<dl class="toc">
<dt>
<span class="section">
<a href="document-store-interfaces.html">
22.1 Interfaces to a MySQL Document Store
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="document-store-concepts.html">
22.2 Document Store Concepts
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="mysql-shell-tutorial-javascript.html">
22.3 JavaScript Quick-Start Guide: MySQL Shell for Document Store
</a>
</span>
</dt>
<dd>
<dl>
<dt>
<span class="section">
<a href="mysql-shell-tutorial-javascript-shell.html">
22.3.1 MySQL Shell
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="mysql-shell-tutorial-javascript-download.html">
22.3.2 Download and Import world_x Database
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="mysql-shell-tutorial-javascript-documents-collections.html">
22.3.3 Documents and Collections
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="mysql-shell-tutorial-javascript-relational-tables.html">
22.3.4 Relational Tables
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="mysql-shell-tutorial-javascript-documents-in-tables.html">
22.3.5 Documents in Tables
</a>
</span>
</dt>
</dl>
</dd>
<dt>
<span class="section">
<a href="mysql-shell-tutorial-python.html">
22.4 Python Quick-Start Guide: MySQL Shell for Document Store
</a>
</span>
</dt>
<dd>
<dl>
<dt>
<span class="section">
<a href="mysql-shell-tutorial-python-shell.html">
22.4.1 MySQL Shell
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="mysql-shell-tutorial-python-download.html">
22.4.2 Download and Import world_x Database
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="mysql-shell-tutorial-python-documents-collections.html">
22.4.3 Documents and Collections
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="mysql-shell-tutorial-python-relational-tables.html">
22.4.4 Relational Tables
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="mysql-shell-tutorial-python-documents-in-tables.html">
22.4.5 Documents in Tables
</a>
</span>
</dt>
</dl>
</dd>
<dt>
<span class="section">
<a href="x-plugin.html">
22.5 X Plugin
</a>
</span>
</dt>
<dd>
<dl>
<dt>
<span class="section">
<a href="x-plugin-checking-installation.html">
22.5.1 Checking X Plugin Installation
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="x-plugin-disabling.html">
22.5.2 Disabling X Plugin
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="x-plugin-encrypted-connections.html">
22.5.3 Using Encrypted Connections with X Plugin
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="x-plugin-sha2-cache-plugin.html">
22.5.4 Using X Plugin with the Caching SHA-2 Authentication Plugin
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="x-plugin-connection-compression.html">
22.5.5 Connection Compression with X Plugin
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="x-plugin-options-variables.html">
22.5.6 X Plugin Options and Variables
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="x-plugin-system-monitoring.html">
22.5.7 Monitoring X Plugin
</a>
</span>
</dt>
</dl>
</dd>
</dl>
</div>
<a class="indexterm" name="idm46045128173776">
</a>
<a class="indexterm" name="idm46045128172736">
</a>
<a class="indexterm" name="idm46045128171248">
</a>
<p>
This chapter introduces an alternative way of working with MySQL as
a document store, sometimes referred to as
<span class="quote">
“
<span class="quote">
using
NoSQL
</span>
”
</span>
. If your intention is to use MySQL in a traditional
(SQL) way, this chapter is probably not relevant to you.
</p>
<p>
Traditionally, relational databases such as MySQL have usually
required a schema to be defined before documents can be stored. The
features described in this section enable you to use MySQL as a
document store, which is a schema-less, and therefore
schema-flexible, storage system for documents. For example, when you
create documents describing products, you do not need to know and
define all possible attributes of any products before storing and
operating with the documents. This differs from working with a
relational database and storing products in a table, when all
columns of the table must be known and defined before adding any
products to the database. The features described in this chapter
enable you to choose how you configure MySQL, using only the
document store model, or combining the flexibility of the document
store model with the power of the relational model.
</p>
<p>
To use MySQL as a document store, you use the following server
features:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
X Plugin enables MySQL Server to communicate with clients using
X Protocol, which is a prerequisite for using MySQL as a
document store. X Plugin is enabled by default in MySQL Server
as of MySQL 8.4. For instructions to verify X
Plugin installation and to configure and monitor X Plugin, see
<a class="xref" href="x-plugin.html" title="22.5 X Plugin">
Section 22.5, “X Plugin”
</a>
.
</p>
</li>
<li class="listitem">
<p>
X Protocol supports both CRUD and SQL operations,
authentication via SASL, allows streaming (pipelining) of
commands and is extensible on the protocol and the message
layer. Clients compatible with X Protocol include MySQL Shell
and MySQL 8.4 Connectors.
</p>
</li>
<li class="listitem">
<p>
Clients that communicate with a MySQL Server using X Protocol
can use X DevAPI to develop applications. X DevAPI offers a
modern programming interface with a simple yet powerful design
which provides support for established industry standard
concepts. This chapter explains how to get started using either
the JavaScript or Python implementation of X DevAPI in
MySQL Shell as a client. See
<a class="ulink" href="/doc/x-devapi-userguide/en/" target="_top">
X DevAPI User Guide
</a>
for in-depth tutorials on
using X DevAPI.
</p>
</li>
</ul>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/mysql-cluster-replication-abbreviations.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="mysql-cluster-replication-abbreviations">
</a>
25.7.1 NDB Cluster Replication: Abbreviations and Symbols
</h3>
</div>
</div>
</div>
<a class="indexterm" name="idm46045086809936">
</a>
<p>
Throughout this section, we use the following abbreviations or
symbols for referring to the source and replica clusters, and to
processes and commands run on the clusters or cluster nodes:
</p>
<div class="table">
<a name="idm46045086807840">
</a>
<p class="title">
<b>
Table 25.41 Abbreviations used throughout this section referring to source
and replica clusters, and to processes and
commands run on cluster nodes
</b>
</p>
<div class="table-contents">
<table>
<colgroup>
<col style="width: 25%"/>
<col style="width: 75%"/>
</colgroup>
<thead>
<tr>
<th>
Symbol or Abbreviation
</th>
<th>
Description (Refers to...)
</th>
</tr>
</thead>
<tbody>
<tr>
<td>
<em class="replaceable">
<code>
S
</code>
</em>
</td>
<td>
The cluster serving as the (primary) replication source
</td>
</tr>
<tr>
<td>
<em class="replaceable">
<code>
R
</code>
</em>
</td>
<td>
The cluster acting as the (primary) replica
</td>
</tr>
<tr>
<td>
<code class="literal">
shell
<em class="replaceable">
<code>
S
</code>
</em>
>
</code>
</td>
<td>
Shell command to be issued on the source cluster
</td>
</tr>
<tr>
<td>
<code class="literal">
mysql
<em class="replaceable">
<code>
S
</code>
</em>
>
</code>
</td>
<td>
MySQL client command issued on a single MySQL server running as an SQL
node on the source cluster
</td>
</tr>
<tr>
<td>
<code class="literal">
mysql
<em class="replaceable">
<code>
S*
</code>
</em>
>
</code>
</td>
<td>
MySQL client command to be issued on all SQL nodes participating in the
replication source cluster
</td>
</tr>
<tr>
<td>
<code class="literal">
shell
<em class="replaceable">
<code>
R
</code>
</em>
>
</code>
</td>
<td>
Shell command to be issued on the replica cluster
</td>
</tr>
<tr>
<td>
<code class="literal">
mysql
<em class="replaceable">
<code>
R
</code>
</em>
>
</code>
</td>
<td>
MySQL client command issued on a single MySQL server running as an SQL
node on the replica cluster
</td>
</tr>
<tr>
<td>
<code class="literal">
mysql
<em class="replaceable">
<code>
R*
</code>
</em>
>
</code>
</td>
<td>
MySQL client command to be issued on all SQL nodes participating in the
replica cluster
</td>
</tr>
<tr>
<td>
<em class="replaceable">
<code>
C
</code>
</em>
</td>
<td>
Primary replication channel
</td>
</tr>
<tr>
<td>
<em class="replaceable">
<code>
C'
</code>
</em>
</td>
<td>
Secondary replication channel
</td>
</tr>
<tr>
<td>
<em class="replaceable">
<code>
S'
</code>
</em>
</td>
<td>
Secondary replication source
</td>
</tr>
<tr>
<td>
<em class="replaceable">
<code>
R'
</code>
</em>
</td>
<td>
Secondary replica
</td>
</tr>
</tbody>
</table>
</div>
<div class="table-contents">
<table cellpadding="0" cellspacing="0" style="position: fixed; top: 0px; display: none; left: 401px; width: 739px;">
<thead>
<tr>
<th style="width: 184.5px;">
Symbol or Abbreviation
</th>
<th style="width: 553.5px;">
Description (Refers to...)
</th>
</tr>
</thead>
</table>
</div>
</div>
<br class="table-break"/>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/date-and-time-types.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h2 class="title">
<a name="date-and-time-types">
</a>
13.2 Date and Time Data Types
</h2>
</div>
</div>
</div>
<div class="toc">
<dl class="toc">
<dt>
<span class="section">
<a href="date-and-time-type-syntax.html">
13.2.1 Date and Time Data Type Syntax
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="datetime.html">
13.2.2 The DATE, DATETIME, and TIMESTAMP Types
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="time.html">
13.2.3 The TIME Type
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="year.html">
13.2.4 The YEAR Type
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="timestamp-initialization.html">
13.2.5 Automatic Initialization and Updating for TIMESTAMP and DATETIME
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="fractional-seconds.html">
13.2.6 Fractional Seconds in Time Values
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="mysql-calendar.html">
13.2.7 What Calendar Is Used By MySQL?
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="date-and-time-type-conversion.html">
13.2.8 Conversion Between Date and Time Types
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="two-digit-years.html">
13.2.9 2-Digit Years in Dates
</a>
</span>
</dt>
</dl>
</div>
<a class="indexterm" name="idm46045213881536">
</a>
<a class="indexterm" name="idm46045213880080">
</a>
<a class="indexterm" name="idm46045213878592">
</a>
<p>
The date and time data types for representing temporal values are
<a class="link" href="datetime.html" title="13.2.2 The DATE, DATETIME, and TIMESTAMP Types">
<code class="literal">
DATE
</code>
</a>
,
<a class="link" href="time.html" title="13.2.3 The TIME Type">
<code class="literal">
TIME
</code>
</a>
,
<a class="link" href="datetime.html" title="13.2.2 The DATE, DATETIME, and TIMESTAMP Types">
<code class="literal">
DATETIME
</code>
</a>
,
<a class="link" href="datetime.html" title="13.2.2 The DATE, DATETIME, and TIMESTAMP Types">
<code class="literal">
TIMESTAMP
</code>
</a>
, and
<a class="link" href="year.html" title="13.2.4 The YEAR Type">
<code class="literal">
YEAR
</code>
</a>
. Each temporal type has a
range of valid values, as well as a
<span class="quote">
“
<span class="quote">
zero
</span>
”
</span>
value that
may be used when you specify an invalid value that MySQL cannot
represent. The
<a class="link" href="datetime.html" title="13.2.2 The DATE, DATETIME, and TIMESTAMP Types">
<code class="literal">
TIMESTAMP
</code>
</a>
and
<a class="link" href="datetime.html" title="13.2.2 The DATE, DATETIME, and TIMESTAMP Types">
<code class="literal">
DATETIME
</code>
</a>
types have special
automatic updating behavior, described in
<a class="xref" href="timestamp-initialization.html" title="13.2.5 Automatic Initialization and Updating for TIMESTAMP and DATETIME">
Section 13.2.5, “Automatic Initialization and Updating for TIMESTAMP and DATETIME”
</a>
.
</p>
<p>
For information about storage requirements of the temporal data
types, see
<a class="xref" href="storage-requirements.html" title="13.7 Data Type Storage Requirements">
Section 13.7, “Data Type Storage Requirements”
</a>
.
</p>
<p>
For descriptions of functions that operate on temporal values, see
<a class="xref" href="date-and-time-functions.html" title="14.7 Date and Time Functions">
Section 14.7, “Date and Time Functions”
</a>
.
</p>
<p>
Keep in mind these general considerations when working with date
and time types:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
MySQL retrieves values for a given date or time type in a
standard output format, but it attempts to interpret a variety
of formats for input values that you supply (for example, when
you specify a value to be assigned to or compared to a date or
time type). For a description of the permitted formats for
date and time types, see
<a class="xref" href="date-and-time-literals.html" title="11.1.3 Date and Time Literals">
Section 11.1.3, “Date and Time Literals”
</a>
. It is expected that
you supply valid values. Unpredictable results may occur if
you use values in other formats.
</p>
</li>
<li class="listitem">
<p>
Although MySQL tries to interpret values in several formats,
date parts must always be given in year-month-day order (for
example,
<code class="literal">
'98-09-04'
</code>
), rather than in the
month-day-year or day-month-year orders commonly used
elsewhere (for example,
<code class="literal">
'09-04-98'
</code>
,
<code class="literal">
'04-09-98'
</code>
). To convert strings in other
orders to year-month-day order, the
<a class="link" href="date-and-time-functions.html#function_str-to-date">
<code class="literal">
STR_TO_DATE()
</code>
</a>
function may be
useful.
</p>
</li>
<li class="listitem">
<p>
Dates containing 2-digit year values are ambiguous because the
century is unknown. MySQL interprets 2-digit year values using
these rules:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<p>
Year values in the range
<code class="literal">
70-99
</code>
become
<code class="literal">
1970-1999
</code>
.
</p>
</li>
<li class="listitem">
<p>
Year values in the range
<code class="literal">
00-69
</code>
become
<code class="literal">
2000-2069
</code>
.
</p>
</li>
</ul>
</div>
<p>
See also
<a class="xref" href="two-digit-years.html" title="13.2.9 2-Digit Years in Dates">
Section 13.2.9, “2-Digit Years in Dates”
</a>
.
</p>
</li>
<li class="listitem">
<p>
Conversion of values from one temporal type to another occurs
according to the rules in
<a class="xref" href="date-and-time-type-conversion.html" title="13.2.8 Conversion Between Date and Time Types">
Section 13.2.8, “Conversion Between Date and Time Types”
</a>
.
</p>
</li>
<li class="listitem">
<p>
MySQL automatically converts a date or time value to a number
if the value is used in numeric context and vice versa.
</p>
</li>
<li class="listitem">
<p>
By default, when MySQL encounters a value for a date or time
type that is out of range or otherwise invalid for the type,
it converts the value to the
<span class="quote">
“
<span class="quote">
zero
</span>
”
</span>
value for
that type. The exception is that out-of-range
<a class="link" href="time.html" title="13.2.3 The TIME Type">
<code class="literal">
TIME
</code>
</a>
values are clipped to the
appropriate endpoint of the
<a class="link" href="time.html" title="13.2.3 The TIME Type">
<code class="literal">
TIME
</code>
</a>
range.
</p>
</li>
<li class="listitem">
<p>
By setting the SQL mode to the appropriate value, you can
specify more exactly what kind of dates you want MySQL to
support. (See
<a class="xref" href="sql-mode.html" title="7.1.11 Server SQL Modes">
Section 7.1.11, “Server SQL Modes”
</a>
.) You can get MySQL
to accept certain dates, such as
<code class="literal">
'2009-11-31'
</code>
, by enabling the
<a class="link" href="sql-mode.html#sqlmode_allow_invalid_dates">
<code class="literal">
ALLOW_INVALID_DATES
</code>
</a>
SQL
mode. This is useful when you want to store a
<span class="quote">
“
<span class="quote">
possibly
wrong
</span>
”
</span>
value which the user has specified (for example,
in a web form) in the database for future processing. Under
this mode, MySQL verifies only that the month is in the range
from 1 to 12 and that the day is in the range from 1 to 31.
</p>
</li>
<li class="listitem">
<p>
MySQL permits you to store dates where the day or month and
day are zero in a
<a class="link" href="datetime.html" title="13.2.2 The DATE, DATETIME, and TIMESTAMP Types">
<code class="literal">
DATE
</code>
</a>
or
<a class="link" href="datetime.html" title="13.2.2 The DATE, DATETIME, and TIMESTAMP Types">
<code class="literal">
DATETIME
</code>
</a>
column. This is useful
for applications that need to store birthdates for which you
may not know the exact date. In this case, you simply store
the date as
<code class="literal">
'2009-00-00'
</code>
or
<code class="literal">
'2009-01-00'
</code>
. However, with dates such as
these, you should not expect to get correct results for
functions such as
<a class="link" href="date-and-time-functions.html#function_date-sub">
<code class="literal">
DATE_SUB()
</code>
</a>
or
<a class="link" href="date-and-time-functions.html#function_date-add">
<code class="literal">
DATE_ADD()
</code>
</a>
that require
complete dates. To disallow zero month or day parts in dates,
enable the
<a class="link" href="sql-mode.html#sqlmode_no_zero_in_date">
<code class="literal">
NO_ZERO_IN_DATE
</code>
</a>
mode.
</p>
</li>
<li class="listitem">
<p>
MySQL permits you to store a
<span class="quote">
“
<span class="quote">
zero
</span>
”
</span>
value of
<code class="literal">
'0000-00-00'
</code>
as a
<span class="quote">
“
<span class="quote">
dummy
date.
</span>
”
</span>
In some cases, this is more convenient than
using
<code class="literal">
NULL
</code>
values, and uses less data and
index space. To disallow
<code class="literal">
'0000-00-00'
</code>
,
enable the
<a class="link" href="sql-mode.html#sqlmode_no_zero_date">
<code class="literal">
NO_ZERO_DATE
</code>
</a>
mode.
</p>
</li>
<li class="listitem">
<p>
<span class="quote">
“
<span class="quote">
Zero
</span>
”
</span>
date or time values used through
Connector/ODBC are converted automatically to
<code class="literal">
NULL
</code>
because ODBC cannot handle such
values.
</p>
</li>
</ul>
</div>
<p>
The following table shows the format of the
<span class="quote">
“
<span class="quote">
zero
</span>
”
</span>
value for each type. The
<span class="quote">
“
<span class="quote">
zero
</span>
”
</span>
values are special,
but you can store or refer to them explicitly using the values
shown in the table. You can also do this using the values
<code class="literal">
'0'
</code>
or
<code class="literal">
0
</code>
, which are easier
to write. For temporal types that include a date part
(
<a class="link" href="datetime.html" title="13.2.2 The DATE, DATETIME, and TIMESTAMP Types">
<code class="literal">
DATE
</code>
</a>
,
<a class="link" href="datetime.html" title="13.2.2 The DATE, DATETIME, and TIMESTAMP Types">
<code class="literal">
DATETIME
</code>
</a>
, and
<a class="link" href="datetime.html" title="13.2.2 The DATE, DATETIME, and TIMESTAMP Types">
<code class="literal">
TIMESTAMP
</code>
</a>
), use of these values may
produce warning or errors. The precise behavior depends on which,
if any, of the strict and
<a class="link" href="sql-mode.html#sqlmode_no_zero_date">
<code class="literal">
NO_ZERO_DATE
</code>
</a>
SQL modes are
enabled; see
<a class="xref" href="sql-mode.html" title="7.1.11 Server SQL Modes">
Section 7.1.11, “Server SQL Modes”
</a>
.
</p>
<div class="informaltable">
<table summary="Format of the zero value for temporal data types.">
<colgroup>
<col style="width: 30%"/>
<col style="width: 40%"/>
</colgroup>
<thead>
<tr>
<th>
Data Type
</th>
<th>
<span class="quote">
“
<span class="quote">
Zero
</span>
”
</span>
Value
</th>
</tr>
</thead>
<tbody>
<tr>
<td>
<a class="link" href="datetime.html" title="13.2.2 The DATE, DATETIME, and TIMESTAMP Types">
<code class="literal">
DATE
</code>
</a>
</td>
<td>
<code class="literal">
'0000-00-00'
</code>
</td>
</tr>
<tr>
<td>
<a class="link" href="time.html" title="13.2.3 The TIME Type">
<code class="literal">
TIME
</code>
</a>
</td>
<td>
<code class="literal">
'00:00:00'
</code>
</td>
</tr>
<tr>
<td>
<a class="link" href="datetime.html" title="13.2.2 The DATE, DATETIME, and TIMESTAMP Types">
<code class="literal">
DATETIME
</code>
</a>
</td>
<td>
<code class="literal">
'0000-00-00 00:00:00'
</code>
</td>
</tr>
<tr>
<td>
<a class="link" href="datetime.html" title="13.2.2 The DATE, DATETIME, and TIMESTAMP Types">
<code class="literal">
TIMESTAMP
</code>
</a>
</td>
<td>
<code class="literal">
'0000-00-00 00:00:00'
</code>
</td>
</tr>
<tr>
<td>
<a class="link" href="year.html" title="13.2.4 The YEAR Type">
<code class="literal">
YEAR
</code>
</a>
</td>
<td>
<code class="literal">
0000
</code>
</td>
</tr>
</tbody>
</table>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/group-replication-distributed-recovery-securing.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="group-replication-distributed-recovery-securing">
</a>
20.6.3 Securing Distributed Recovery Connections
</h3>
</div>
</div>
</div>
<div class="toc">
<dl class="toc">
<dt>
<span class="section">
<a href="group-replication-secure-user.html">
20.6.3.1 Secure User Credentials for Distributed Recovery
</a>
</span>
</dt>
<dt>
<span class="section">
<a href="group-replication-configuring-ssl-for-recovery.html">
20.6.3.2 Secure Socket Layer (SSL) Connections for Distributed Recovery
</a>
</span>
</dt>
</dl>
</div>
<div class="important" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Important
</div>
<p>
When using the MySQL communication stack
(
<a class="link" href="group-replication-system-variables.html#sysvar_group_replication_communication_stack">
<code class="literal">
group_replication_communication_stack=MYSQL
</code>
</a>
)
AND secure connections between members
(
<a class="link" href="group-replication-system-variables.html#sysvar_group_replication_ssl_mode">
<code class="literal">
group_replication_ssl_mode
</code>
</a>
is
not set to
<code class="literal">
DISABLED
</code>
), the security settings
discussed in this section are applied not just to distributed
recovery connections, but to group communications between
members in general.
</p>
</div>
<p>
When a member joins the group, distributed recovery is carried out
using a combination of a remote cloning operation, if available
and appropriate, and an asynchronous replication connection. For a
full description of distributed recovery, see
<a class="xref" href="group-replication-distributed-recovery.html" title="20.5.4 Distributed Recovery">
Section 20.5.4, “Distributed Recovery”
</a>
.
</p>
<p>
Group members offer their standard SQL client connection to
joining members for distributed recovery, as specified by MySQL
Server's
<a class="link" href="server-system-variables.html#sysvar_hostname">
<code class="literal">
hostname
</code>
</a>
and
<a class="link" href="server-system-variables.html#sysvar_port">
<code class="literal">
port
</code>
</a>
system variables, and may
(also) advertise an alternative list of distributed recovery
endpoints as dedicated client connections for joining members. For
more details, see
<a class="xref" href="group-replication-distributed-recovery-connections.html" title="20.5.4.1 Connections for Distributed Recovery">
Section 20.5.4.1, “Connections for Distributed Recovery”
</a>
.
Notice that such connections offered to a joining member for
distributed recovery is
<span class="emphasis">
<em>
not
</em>
</span>
the same
connections that are used by Group Replication for communication
between online members when the XCom communication stack is used
for group communications
(
<a class="link" href="group-replication-system-variables.html#sysvar_group_replication_communication_stack">
<code class="literal">
group_replication_communication_stack=XCOM
</code>
</a>
).
</p>
<p>
To secure distributed recovery connections in the group, ensure
that user credentials for the replication user are properly
secured, and use SSL for distributed recovery connections if
possible.
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/mysql-cluster-ndbinfo-cpudata-1sec.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="mysql-cluster-ndbinfo-cpudata-1sec">
</a>
25.6.17.15 The ndbinfo cpudata_1sec Table
</h4>
</div>
</div>
</div>
<a class="indexterm" name="idm46045090037136">
</a>
<p>
The
<code class="literal">
cpudata_1sec
</code>
table provides data about
CPU usage per second over the last 20 seconds.
</p>
<p>
The
<code class="literal">
cpustat
</code>
table contains the following
columns:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<code class="literal">
node_id
</code>
</p>
<p>
Node ID
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
measurement_id
</code>
</p>
<p>
Measurement sequence ID; later measurements have lower IDs
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
cpu_no
</code>
</p>
<p>
CPU ID
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
cpu_online
</code>
</p>
<p>
1 if the CPU is currently online, otherwise 0
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
cpu_userspace_time
</code>
</p>
<p>
CPU time spent in userspace
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
cpu_idle_time
</code>
</p>
<p>
CPU time spent idle
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
cpu_system_time
</code>
</p>
<p>
CPU time spent in system time
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
cpu_interrupt_time
</code>
</p>
<p>
CPU time spent handling interrupts (hardware and software)
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
cpu_exec_vm_time
</code>
</p>
<p>
CPU time spent in virtual machine execution
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
elapsed_time
</code>
</p>
<p>
Time in microseconds used for this measurement
</p>
</li>
</ul>
</div>
<h5>
<a name="idm46045090013760">
</a>
Notes
</h5>
<p>
The
<code class="literal">
cpudata_1sec
</code>
table is available only on
Linux and Solaris operating systems.
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/myisam-optimization.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="myisam-optimization">
</a>
9.6.4 MyISAM Table Optimization
</h3>
</div>
</div>
</div>
<a class="indexterm" name="idm46045230482032">
</a>
<a class="indexterm" name="idm46045230480576">
</a>
<p>
To coalesce fragmented rows and eliminate wasted space that
results from deleting or updating rows, run
<a class="link" href="myisamchk.html" title="6.6.4 myisamchk — MyISAM Table-Maintenance Utility">
<span class="command">
<strong>
myisamchk
</strong>
</span>
</a>
in recovery mode:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-terminal"><div class="docs-select-all right" id="sa74323940"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-terminal"><span class="token prompt">$> </span><span class="token command">myisamchk</span> <span class="token property">-r</span> <em class="replaceable">tbl_name</em></code></pre>
</div>
<p>
You can optimize a table in the same way by using the
<a class="link" href="optimize-table.html" title="15.7.3.4 OPTIMIZE TABLE Statement">
<code class="literal">
OPTIMIZE TABLE
</code>
</a>
SQL statement.
<a class="link" href="optimize-table.html" title="15.7.3.4 OPTIMIZE TABLE Statement">
<code class="literal">
OPTIMIZE TABLE
</code>
</a>
does a table
repair and a key analysis, and also sorts the index tree so that
key lookups are faster. There is also no possibility of unwanted
interaction between a utility and the server, because the server
does all the work when you use
<a class="link" href="optimize-table.html" title="15.7.3.4 OPTIMIZE TABLE Statement">
<code class="literal">
OPTIMIZE
TABLE
</code>
</a>
. See
<a class="xref" href="optimize-table.html" title="15.7.3.4 OPTIMIZE TABLE Statement">
Section 15.7.3.4, “OPTIMIZE TABLE Statement”
</a>
.
</p>
<p>
<a class="link" href="myisamchk.html" title="6.6.4 myisamchk — MyISAM Table-Maintenance Utility">
<span class="command">
<strong>
myisamchk
</strong>
</span>
</a>
has a number of other options that
you can use to improve the performance of a table:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<a class="link" href="myisamchk-other-options.html#option_myisamchk_analyze">
<code class="option">
--analyze
</code>
</a>
or
<code class="option">
-a
</code>
: Perform key distribution analysis. This
improves join performance by enabling the join optimizer to
better choose the order in which to join the tables and
which indexes it should use.
</p>
</li>
<li class="listitem">
<p>
<a class="link" href="myisamchk-other-options.html#option_myisamchk_sort-index">
<code class="option">
--sort-index
</code>
</a>
or
<code class="option">
-S
</code>
: Sort the index blocks. This optimizes
seeks and makes table scans that use indexes faster.
</p>
</li>
<li class="listitem">
<p>
<a class="link" href="myisamchk-other-options.html#option_myisamchk_sort-records">
<code class="option">
--sort-records=
<em class="replaceable">
<code>
index_num
</code>
</em>
</code>
</a>
or
<code class="option">
-R
<em class="replaceable">
<code>
index_num
</code>
</em>
</code>
:
Sort data rows according to a given index. This makes your
data much more localized and may speed up range-based
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT
</code>
</a>
and
<code class="literal">
ORDER
BY
</code>
operations that use this index.
</p>
</li>
</ul>
</div>
<p>
For a full description of all available options, see
<a class="xref" href="myisamchk.html" title="6.6.4 myisamchk — MyISAM Table-Maintenance Utility">
Section 6.6.4, “myisamchk — MyISAM Table-Maintenance Utility”
</a>
.
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/create-role.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="create-role">
</a>
15.7.1.2 CREATE ROLE Statement
</h4>
</div>
</div>
</div>
<a class="indexterm" name="idm46045174601760">
</a>
<a class="indexterm" name="idm46045174600688">
</a>
<a class="indexterm" name="idm46045174599200">
</a>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa14920297"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">ROLE</span> <span class="token punctuation">[</span><span class="token keyword">IF</span> <span class="token operator">NOT</span> <span class="token keyword">EXISTS</span><span class="token punctuation">]</span> <span class="token keyword"><em class="replaceable">role</em></span> <span class="token punctuation">[</span><span class="token punctuation">,</span> <span class="token keyword"><em class="replaceable">role</em></span> <span class="token punctuation">]</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span></code></pre>
</div>
<p>
<a class="link" href="create-role.html" title="15.7.1.2 CREATE ROLE Statement">
<code class="literal">
CREATE ROLE
</code>
</a>
creates one or more
roles, which are named collections of privileges. To use this
statement, you must have the global
<a class="link" href="privileges-provided.html#priv_create-role">
<code class="literal">
CREATE
ROLE
</code>
</a>
or
<a class="link" href="privileges-provided.html#priv_create-user">
<code class="literal">
CREATE USER
</code>
</a>
privilege. When the
<a class="link" href="server-system-variables.html#sysvar_read_only">
<code class="literal">
read_only
</code>
</a>
system variable is enabled,
<a class="link" href="create-role.html" title="15.7.1.2 CREATE ROLE Statement">
<code class="literal">
CREATE
ROLE
</code>
</a>
additionally requires the
<a class="link" href="privileges-provided.html#priv_connection-admin">
<code class="literal">
CONNECTION_ADMIN
</code>
</a>
privilege (or
the deprecated
<a class="link" href="privileges-provided.html#priv_super">
<code class="literal">
SUPER
</code>
</a>
privilege).
</p>
<p>
A role when created is locked, has no password, and is assigned
the default authentication plugin. (These role attributes can be
changed later with the
<a class="link" href="alter-user.html" title="15.7.1.1 ALTER USER Statement">
<code class="literal">
ALTER USER
</code>
</a>
statement, by users who have the global
<a class="link" href="privileges-provided.html#priv_create-user">
<code class="literal">
CREATE USER
</code>
</a>
privilege.)
</p>
<p>
<a class="link" href="create-role.html" title="15.7.1.2 CREATE ROLE Statement">
<code class="literal">
CREATE ROLE
</code>
</a>
either succeeds for
all named roles or rolls back and has no effect if any error
occurs. By default, an error occurs if you try to create a role
that already exists. If the
<code class="literal">
IF NOT EXISTS
</code>
clause is given, the statement produces a warning for each named
role that already exists, rather than an error.
</p>
<p>
The statement is written to the binary log if it succeeds, but
not if it fails; in that case, rollback occurs and no changes
are made. A statement written to the binary log includes all
named roles. If the
<code class="literal">
IF NOT EXISTS
</code>
clause is
given, this includes even roles that already exist and were not
created.
</p>
<p>
Each role name uses the format described in
<a class="xref" href="role-names.html" title="8.2.5 Specifying Role Names">
Section 8.2.5, “Specifying Role Names”
</a>
. For example:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa66257591"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">ROLE</span> <span class="token string">'admin'</span><span class="token punctuation">,</span> <span class="token string">'developer'</span><span class="token punctuation">;</span>
<span class="token keyword">CREATE</span> <span class="token keyword">ROLE</span> <span class="token string">'webapp'</span>@<span class="token string">'localhost'</span><span class="token punctuation">;</span></code></pre>
</div>
<p>
The host name part of the role name, if omitted, defaults to
<code class="literal">
'%'
</code>
.
</p>
<p>
For role usage examples, see
<a class="xref" href="roles.html" title="8.2.10 Using Roles">
Section 8.2.10, “Using Roles”
</a>
.
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/charset-table.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="charset-table">
</a>
12.3.4 Table Character Set and Collation
</h3>
</div>
</div>
</div>
<p>
Every table has a table character set and a table collation. The
<a class="link" href="create-table.html" title="15.1.20 CREATE TABLE Statement">
<code class="literal">
CREATE TABLE
</code>
</a>
and
<a class="link" href="alter-table.html" title="15.1.9 ALTER TABLE Statement">
<code class="literal">
ALTER TABLE
</code>
</a>
statements have
optional clauses for specifying the table character set and
collation:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa79487689"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> <em class="replaceable">tbl_name</em> <span class="token punctuation">(</span><em class="replaceable">column_list</em><span class="token punctuation">)</span>
<span class="token punctuation">[</span><span class="token punctuation">[</span><span class="token keyword">DEFAULT</span><span class="token punctuation">]</span> <span class="token keyword">CHARACTER</span> <span class="token keyword">SET</span> <em class="replaceable">charset_name</em><span class="token punctuation">]</span>
<span class="token punctuation">[</span><span class="token keyword">COLLATE</span> <em class="replaceable">collation_name</em><span class="token punctuation">]</span><span class="token punctuation">]</span>
<span class="token keyword">ALTER</span> <span class="token keyword">TABLE</span> <em class="replaceable">tbl_name</em>
<span class="token punctuation">[</span><span class="token punctuation">[</span><span class="token keyword">DEFAULT</span><span class="token punctuation">]</span> <span class="token keyword">CHARACTER</span> <span class="token keyword">SET</span> <em class="replaceable">charset_name</em><span class="token punctuation">]</span>
<span class="token punctuation">[</span><span class="token keyword">COLLATE</span> <em class="replaceable">collation_name</em><span class="token punctuation">]</span></code></pre>
</div>
<p>
Example:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa14420203"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> t1 <span class="token punctuation">(</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span> <span class="token punctuation">)</span>
<span class="token keyword">CHARACTER</span> <span class="token keyword">SET</span> latin1 <span class="token keyword">COLLATE</span> latin1_danish_ci<span class="token punctuation">;</span></code></pre>
</div>
<p>
MySQL chooses the table character set and collation in the
following manner:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
If both
<code class="literal">
CHARACTER SET
<em class="replaceable">
<code>
charset_name
</code>
</em>
</code>
and
<code class="literal">
COLLATE
<em class="replaceable">
<code>
collation_name
</code>
</em>
</code>
are
specified, character set
<em class="replaceable">
<code>
charset_name
</code>
</em>
and collation
<em class="replaceable">
<code>
collation_name
</code>
</em>
are used.
</p>
</li>
<li class="listitem">
<p>
If
<code class="literal">
CHARACTER SET
<em class="replaceable">
<code>
charset_name
</code>
</em>
</code>
is
specified without
<code class="literal">
COLLATE
</code>
, character set
<em class="replaceable">
<code>
charset_name
</code>
</em>
and its default
collation are used. To see the default collation for each
character set, use the
<a class="link" href="show-character-set.html" title="15.7.7.4 SHOW CHARACTER SET Statement">
<code class="literal">
SHOW CHARACTER
SET
</code>
</a>
statement or query the
<code class="literal">
INFORMATION_SCHEMA
</code>
<a class="link" href="information-schema-character-sets-table.html" title="28.3.4 The INFORMATION_SCHEMA CHARACTER_SETS Table">
<code class="literal">
CHARACTER_SETS
</code>
</a>
table.
</p>
</li>
<li class="listitem">
<p>
If
<code class="literal">
COLLATE
<em class="replaceable">
<code>
collation_name
</code>
</em>
</code>
is
specified without
<code class="literal">
CHARACTER SET
</code>
, the
character set associated with
<em class="replaceable">
<code>
collation_name
</code>
</em>
and collation
<em class="replaceable">
<code>
collation_name
</code>
</em>
are used.
</p>
</li>
<li class="listitem">
<p>
Otherwise (neither
<code class="literal">
CHARACTER SET
</code>
nor
<code class="literal">
COLLATE
</code>
is specified), the database
character set and collation are used.
</p>
</li>
</ul>
</div>
<p>
The table character set and collation are used as default values
for column definitions if the column character set and collation
are not specified in individual column definitions. The table
character set and collation are MySQL extensions; there are no
such things in standard SQL.
</p>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/sys-ps-setup-enable-thread.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="sys-ps-setup-enable-thread">
</a>
30.4.4.11 The ps_setup_enable_thread() Procedure
</h4>
</div>
</div>
</div>
<a class="indexterm" name="idm46045061446496">
</a>
<a class="indexterm" name="idm46045061444992">
</a>
<p>
Given a connection ID, enables Performance Schema
instrumentation for the thread. Produces a result set
indicating how many threads were enabled. Already enabled
threads do not count.
</p>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h5 class="title">
<a name="sys-ps-setup-enable-thread-parameters">
</a>
Parameters
</h5>
</div>
</div>
</div>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<code class="literal">
in_connection_id BIGINT
</code>
: The
connection ID. This is a value of the type given in the
<code class="literal">
PROCESSLIST_ID
</code>
column of the
Performance Schema
<a class="link" href="performance-schema-threads-table.html" title="29.12.22.8 The threads Table">
<code class="literal">
threads
</code>
</a>
table or the
<code class="literal">
Id
</code>
column of
<a class="link" href="show-processlist.html" title="15.7.7.31 SHOW PROCESSLIST Statement">
<code class="literal">
SHOW PROCESSLIST
</code>
</a>
output.
</p>
</li>
</ul>
</div>
</div>
<div class="simplesect">
<div class="titlepage">
<div>
<div class="simple">
<h5 class="title">
<a name="sys-ps-setup-enable-thread-example">
</a>
Example
</h5>
</div>
</div>
</div>
<p>
Enable a specific connection by its connection ID:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa53419056"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">CALL</span> sys<span class="token punctuation">.</span>ps_setup_enable_thread<span class="token punctuation">(</span><span class="token number">225</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> summary <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> Enabled 1 thread <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span></code></pre>
</div>
<p>
Enable the current connection:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa26993596"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">CALL</span> sys<span class="token punctuation">.</span>ps_setup_enable_thread<span class="token punctuation">(</span><span class="token function">CONNECTION_ID</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> summary <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> Enabled 1 thread <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span></code></pre>
</div>
</div>
</div>
<br/>
</div>
|
https://dev.mysql.com/doc/refman/8.4/en/subquery-optimization-with-exists.html | <div id="docs-body">
<div class="section">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="subquery-optimization-with-exists">
</a>
10.2.2.3 Optimizing Subqueries with the EXISTS Strategy
</h4>
</div>
</div>
</div>
<a class="indexterm" name="idm46045228149232">
</a>
<a class="indexterm" name="idm46045228147744">
</a>
<p>
Certain optimizations are applicable to comparisons that use
the
<code class="literal">
IN
</code>
(or
<code class="literal">
=ANY
</code>
)
operator to test subquery results. This section discusses
these optimizations, particularly with regard to the
challenges that
<code class="literal">
NULL
</code>
values present. The
last part of the discussion suggests how you can help the
optimizer.
</p>
<p>
Consider the following subquery comparison:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa88106484"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><em class="replaceable">outer_expr</em> <span class="token keyword">IN</span> <span class="token punctuation">(</span><span class="token keyword">SELECT</span> <em class="replaceable">inner_expr</em> <span class="token keyword">FROM</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span> <span class="token keyword">WHERE</span> <em class="replaceable">subquery_where</em><span class="token punctuation">)</span></code></pre>
</div>
<p>
MySQL evaluates queries
<span class="quote">
“
<span class="quote">
from outside to inside.
</span>
”
</span>
That is, it first obtains the value of the outer expression
<em class="replaceable">
<code>
outer_expr
</code>
</em>
, and then runs the
subquery and captures the rows that it produces.
</p>
<p>
A very useful optimization is to
<span class="quote">
“
<span class="quote">
inform
</span>
”
</span>
the
subquery that the only rows of interest are those where the
inner expression
<em class="replaceable">
<code>
inner_expr
</code>
</em>
is
equal to
<em class="replaceable">
<code>
outer_expr
</code>
</em>
. This is done
by pushing down an appropriate equality into the
subquery's
<code class="literal">
WHERE
</code>
clause to make it
more restrictive. The converted comparison looks like this:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa56355942"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">EXISTS</span> <span class="token punctuation">(</span><span class="token keyword">SELECT</span> <span class="token number">1</span> <span class="token keyword">FROM</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span> <span class="token keyword">WHERE</span> <em class="replaceable">subquery_where</em> <span class="token operator">AND</span> <em class="replaceable">outer_expr</em><span class="token operator">=</span><em class="replaceable">inner_expr</em><span class="token punctuation">)</span></code></pre>
</div>
<p>
After the conversion, MySQL can use the pushed-down equality
to limit the number of rows it must examine to evaluate the
subquery.
</p>
<p>
More generally, a comparison of
<em class="replaceable">
<code>
N
</code>
</em>
values to a subquery that returns
<em class="replaceable">
<code>
N
</code>
</em>
-value rows is subject to the same
conversion. If
<em class="replaceable">
<code>
oe_i
</code>
</em>
and
<em class="replaceable">
<code>
ie_i
</code>
</em>
represent corresponding outer
and inner expression values, this subquery comparison:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa87773366"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token punctuation">(</span><em class="replaceable">oe_1</em><span class="token punctuation">,</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">,</span> <em class="replaceable">oe_N</em><span class="token punctuation">)</span> <span class="token keyword">IN</span>
<span class="token punctuation">(</span><span class="token keyword">SELECT</span> <em class="replaceable">ie_1</em><span class="token punctuation">,</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">,</span> <em class="replaceable">ie_N</em> <span class="token keyword">FROM</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span> <span class="token keyword">WHERE</span> <em class="replaceable">subquery_where</em><span class="token punctuation">)</span></code></pre>
</div>
<p>
Becomes:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa12457591"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">EXISTS</span> <span class="token punctuation">(</span><span class="token keyword">SELECT</span> <span class="token number">1</span> <span class="token keyword">FROM</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span> <span class="token keyword">WHERE</span> <em class="replaceable">subquery_where</em>
<span class="token operator">AND</span> <em class="replaceable">oe_1</em> <span class="token operator">=</span> <em class="replaceable">ie_1</em>
<span class="token operator">AND</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token operator">AND</span> <em class="replaceable">oe_N</em> <span class="token operator">=</span> <em class="replaceable">ie_N</em><span class="token punctuation">)</span></code></pre>
</div>
<p>
For simplicity, the following discussion assumes a single pair
of outer and inner expression values.
</p>
<p>
The
<span class="quote">
“
<span class="quote">
pushdown
</span>
”
</span>
strategy just described works if
either of these conditions is true:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<em class="replaceable">
<code>
outer_expr
</code>
</em>
and
<em class="replaceable">
<code>
inner_expr
</code>
</em>
cannot be
<code class="literal">
NULL
</code>
.
</p>
</li>
<li class="listitem">
<p>
You need not distinguish
<code class="literal">
NULL
</code>
from
<code class="literal">
FALSE
</code>
subquery results. If the subquery
is a part of an
<a class="link" href="logical-operators.html#operator_or">
<code class="literal">
OR
</code>
</a>
or
<a class="link" href="logical-operators.html#operator_and">
<code class="literal">
AND
</code>
</a>
expression in the
<code class="literal">
WHERE
</code>
clause, MySQL assumes that you do
not care. Another instance where the optimizer notices
that
<code class="literal">
NULL
</code>
and
<code class="literal">
FALSE
</code>
subquery results need not be distinguished is this
construct:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa85538461"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span> <span class="token keyword">WHERE</span> <em class="replaceable">outer_expr</em> <span class="token keyword">IN</span> <span class="token punctuation">(</span><em class="replaceable">subquery</em><span class="token punctuation">)</span></code></pre>
</div>
<p>
In this case, the
<code class="literal">
WHERE
</code>
clause rejects
the row whether
<code class="literal">
IN
(
<em class="replaceable">
<code>
subquery
</code>
</em>
)
</code>
returns
<code class="literal">
NULL
</code>
or
<code class="literal">
FALSE
</code>
.
</p>
</li>
</ul>
</div>
<p>
Suppose that
<em class="replaceable">
<code>
outer_expr
</code>
</em>
is known to
be a non-
<code class="literal">
NULL
</code>
value but the subquery does
not produce a row such that
<em class="replaceable">
<code>
outer_expr
</code>
</em>
=
<em class="replaceable">
<code>
inner_expr
</code>
</em>
. Then
<code class="literal">
<em class="replaceable">
<code>
outer_expr
</code>
</em>
IN (SELECT
...)
</code>
evaluates as follows:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<code class="literal">
NULL
</code>
, if the
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT
</code>
</a>
produces any row
where
<em class="replaceable">
<code>
inner_expr
</code>
</em>
is
<code class="literal">
NULL
</code>
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
FALSE
</code>
, if the
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT
</code>
</a>
produces only
non-
<code class="literal">
NULL
</code>
values or produces nothing
</p>
</li>
</ul>
</div>
<p>
In this situation, the approach of looking for rows with
<code class="literal">
<em class="replaceable">
<code>
outer_expr
</code>
</em>
=
<em class="replaceable">
<code>
inner_expr
</code>
</em>
</code>
is no longer
valid. It is necessary to look for such rows, but if none are
found, also look for rows where
<em class="replaceable">
<code>
inner_expr
</code>
</em>
is
<code class="literal">
NULL
</code>
. Roughly speaking, the subquery can be
converted to something like this:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa63572651"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">EXISTS</span> <span class="token punctuation">(</span><span class="token keyword">SELECT</span> <span class="token number">1</span> <span class="token keyword">FROM</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span> <span class="token keyword">WHERE</span> <em class="replaceable">subquery_where</em> <span class="token operator">AND</span>
<span class="token punctuation">(</span><em class="replaceable">outer_expr</em><span class="token operator">=</span><em class="replaceable">inner_expr</em> <span class="token operator">OR</span> <em class="replaceable">inner_expr</em> <span class="token operator">IS</span> <span class="token boolean">NULL</span><span class="token punctuation">)</span><span class="token punctuation">)</span></code></pre>
</div>
<p>
The need to evaluate the extra
<a class="link" href="comparison-operators.html#operator_is-null">
<code class="literal">
IS
NULL
</code>
</a>
condition is why MySQL has the
<a class="link" href="explain-output.html#jointype_ref_or_null">
<code class="literal">
ref_or_null
</code>
</a>
access method:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa7376903"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">EXPLAIN</span>
<span class="token keyword">SELECT</span> <em class="replaceable">outer_expr</em> <span class="token keyword">IN</span> <span class="token punctuation">(</span><span class="token keyword">SELECT</span> t2<span class="token punctuation">.</span>maybe_null_key
<span class="token keyword">FROM</span> t2<span class="token punctuation">,</span> t3 <span class="token keyword">WHERE</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">)</span>
<span class="token keyword">FROM</span> t1<span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span> 1. row <span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span>
id<span class="token punctuation">:</span> 1
select_type<span class="token punctuation">:</span> PRIMARY
table<span class="token punctuation">:</span> t1
...
<span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span> 2. row <span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span>
id<span class="token punctuation">:</span> 2
select_type<span class="token punctuation">:</span> DEPENDENT SUBQUERY
table<span class="token punctuation">:</span> t2
type<span class="token punctuation">:</span> ref_or_null
possible_keys<span class="token punctuation">:</span> maybe_null_key
key<span class="token punctuation">:</span> maybe_null_key
key_len<span class="token punctuation">:</span> 5
ref<span class="token punctuation">:</span> func
rows<span class="token punctuation">:</span> 2
Extra<span class="token punctuation">:</span> Using where; Using index
...</span></code></pre>
</div>
<p>
The
<a class="link" href="explain-output.html#jointype_unique_subquery">
<code class="literal">
unique_subquery
</code>
</a>
and
<a class="link" href="explain-output.html#jointype_index_subquery">
<code class="literal">
index_subquery
</code>
</a>
subquery-specific access methods also have
<span class="quote">
“
<span class="quote">
or
<code class="literal">
NULL
</code>
</span>
”
</span>
variants.
</p>
<p>
The additional
<code class="literal">
OR ... IS NULL
</code>
condition
makes query execution slightly more complicated (and some
optimizations within the subquery become inapplicable), but
generally this is tolerable.
</p>
<p>
The situation is much worse when
<em class="replaceable">
<code>
outer_expr
</code>
</em>
can be
<code class="literal">
NULL
</code>
. According to the SQL interpretation
of
<code class="literal">
NULL
</code>
as
<span class="quote">
“
<span class="quote">
unknown value,
</span>
”
</span>
<code class="literal">
NULL IN (SELECT
<em class="replaceable">
<code>
inner_expr
</code>
</em>
...)
</code>
should evaluate to:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<code class="literal">
NULL
</code>
, if the
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT
</code>
</a>
produces any rows
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
FALSE
</code>
, if the
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT
</code>
</a>
produces no rows
</p>
</li>
</ul>
</div>
<p>
For proper evaluation, it is necessary to be able to check
whether the
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT
</code>
</a>
has produced
any rows at all, so
<code class="literal">
<em class="replaceable">
<code>
outer_expr
</code>
</em>
=
<em class="replaceable">
<code>
inner_expr
</code>
</em>
</code>
cannot be
pushed down into the subquery. This is a problem because many
real world subqueries become very slow unless the equality can
be pushed down.
</p>
<p>
Essentially, there must be different ways to execute the
subquery depending on the value of
<em class="replaceable">
<code>
outer_expr
</code>
</em>
.
</p>
<p>
The optimizer chooses SQL compliance over speed, so it
accounts for the possibility that
<em class="replaceable">
<code>
outer_expr
</code>
</em>
might be
<code class="literal">
NULL
</code>
:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
If
<em class="replaceable">
<code>
outer_expr
</code>
</em>
is
<code class="literal">
NULL
</code>
, to evaluate the following
expression, it is necessary to execute the
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT
</code>
</a>
to determine whether
it produces any rows:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa55297223"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token boolean">NULL</span> <span class="token keyword">IN</span> <span class="token punctuation">(</span><span class="token keyword">SELECT</span> <em class="replaceable">inner_expr</em> <span class="token keyword">FROM</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span> <span class="token keyword">WHERE</span> <em class="replaceable">subquery_where</em><span class="token punctuation">)</span></code></pre>
</div>
<p>
It is necessary to execute the original
<a class="link" href="select.html" title="15.2.13 SELECT Statement">
<code class="literal">
SELECT
</code>
</a>
here, without any
pushed-down equalities of the kind mentioned previously.
</p>
</li>
<li class="listitem">
<p>
On the other hand, when
<em class="replaceable">
<code>
outer_expr
</code>
</em>
is not
<code class="literal">
NULL
</code>
, it is absolutely essential that
this comparison:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa3898127"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><em class="replaceable">outer_expr</em> <span class="token keyword">IN</span> <span class="token punctuation">(</span><span class="token keyword">SELECT</span> <em class="replaceable">inner_expr</em> <span class="token keyword">FROM</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span> <span class="token keyword">WHERE</span> <em class="replaceable">subquery_where</em><span class="token punctuation">)</span></code></pre>
</div>
<p>
Be converted to this expression that uses a pushed-down
condition:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa2473766"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">EXISTS</span> <span class="token punctuation">(</span><span class="token keyword">SELECT</span> <span class="token number">1</span> <span class="token keyword">FROM</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span> <span class="token keyword">WHERE</span> <em class="replaceable">subquery_where</em> <span class="token operator">AND</span> <em class="replaceable">outer_expr</em><span class="token operator">=</span><em class="replaceable">inner_expr</em><span class="token punctuation">)</span></code></pre>
</div>
<p>
Without this conversion, subqueries are slow.
</p>
</li>
</ul>
</div>
<p>
To solve the dilemma of whether or not to push down conditions
into the subquery, the conditions are wrapped within
<span class="quote">
“
<span class="quote">
trigger
</span>
”
</span>
functions. Thus, an expression of the
following form:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa47183186"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><em class="replaceable">outer_expr</em> <span class="token keyword">IN</span> <span class="token punctuation">(</span><span class="token keyword">SELECT</span> <em class="replaceable">inner_expr</em> <span class="token keyword">FROM</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span> <span class="token keyword">WHERE</span> <em class="replaceable">subquery_where</em><span class="token punctuation">)</span></code></pre>
</div>
<p>
Is converted into:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa28131917"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">EXISTS</span> <span class="token punctuation">(</span><span class="token keyword">SELECT</span> <span class="token number">1</span> <span class="token keyword">FROM</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span> <span class="token keyword">WHERE</span> <em class="replaceable">subquery_where</em>
<span class="token operator">AND</span> trigcond<span class="token punctuation">(</span><em class="replaceable">outer_expr</em><span class="token operator">=</span><em class="replaceable">inner_expr</em><span class="token punctuation">)</span><span class="token punctuation">)</span></code></pre>
</div>
<p>
More generally, if the subquery comparison is based on several
pairs of outer and inner expressions, the conversion takes
this comparison:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa77956927"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token punctuation">(</span><em class="replaceable">oe_1</em><span class="token punctuation">,</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">,</span> <em class="replaceable">oe_N</em><span class="token punctuation">)</span> <span class="token keyword">IN</span> <span class="token punctuation">(</span><span class="token keyword">SELECT</span> <em class="replaceable">ie_1</em><span class="token punctuation">,</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">,</span> <em class="replaceable">ie_N</em> <span class="token keyword">FROM</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span> <span class="token keyword">WHERE</span> <em class="replaceable">subquery_where</em><span class="token punctuation">)</span></code></pre>
</div>
<p>
And converts it to this expression:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa83919864"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token keyword">EXISTS</span> <span class="token punctuation">(</span><span class="token keyword">SELECT</span> <span class="token number">1</span> <span class="token keyword">FROM</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span> <span class="token keyword">WHERE</span> <em class="replaceable">subquery_where</em>
<span class="token operator">AND</span> trigcond<span class="token punctuation">(</span><em class="replaceable">oe_1</em><span class="token operator">=</span><em class="replaceable">ie_1</em><span class="token punctuation">)</span>
<span class="token operator">AND</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token operator">AND</span> trigcond<span class="token punctuation">(</span><em class="replaceable">oe_N</em><span class="token operator">=</span><em class="replaceable">ie_N</em><span class="token punctuation">)</span>
<span class="token punctuation">)</span></code></pre>
</div>
<p>
Each
<code class="literal">
trigcond(
<em class="replaceable">
<code>
X
</code>
</em>
)
</code>
is a special function that evaluates to the following values:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
<em class="replaceable">
<code>
X
</code>
</em>
when the
<span class="quote">
“
<span class="quote">
linked
</span>
”
</span>
outer expression
<em class="replaceable">
<code>
oe_i
</code>
</em>
is not
<code class="literal">
NULL
</code>
</p>
</li>
<li class="listitem">
<p>
<code class="literal">
TRUE
</code>
when the
<span class="quote">
“
<span class="quote">
linked
</span>
”
</span>
outer expression
<em class="replaceable">
<code>
oe_i
</code>
</em>
is
<code class="literal">
NULL
</code>
</p>
</li>
</ul>
</div>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<div class="admon-title">
Note
</div>
<p>
Trigger functions are
<span class="emphasis">
<em>
not
</em>
</span>
triggers of
the kind that you create with
<a class="link" href="create-trigger.html" title="15.1.22 CREATE TRIGGER Statement">
<code class="literal">
CREATE
TRIGGER
</code>
</a>
.
</p>
</div>
<p>
Equalities that are wrapped within
<code class="literal">
trigcond()
</code>
functions are not first class
predicates for the query optimizer. Most optimizations cannot
deal with predicates that may be turned on and off at query
execution time, so they assume any
<code class="literal">
trigcond(
<em class="replaceable">
<code>
X
</code>
</em>
)
</code>
to
be an unknown function and ignore it. Triggered equalities can
be used by those optimizations:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
Reference optimizations:
<code class="literal">
trigcond(
<em class="replaceable">
<code>
X
</code>
</em>
=
<em class="replaceable">
<code>
Y
</code>
</em>
[OR
<em class="replaceable">
<code>
Y
</code>
</em>
IS NULL])
</code>
can
be used to construct
<a class="link" href="explain-output.html#jointype_ref">
<code class="literal">
ref
</code>
</a>
,
<a class="link" href="explain-output.html#jointype_eq_ref">
<code class="literal">
eq_ref
</code>
</a>
, or
<a class="link" href="explain-output.html#jointype_ref_or_null">
<code class="literal">
ref_or_null
</code>
</a>
table
accesses.
</p>
</li>
<li class="listitem">
<p>
Index lookup-based subquery execution engines:
<code class="literal">
trigcond(
<em class="replaceable">
<code>
X
</code>
</em>
=
<em class="replaceable">
<code>
Y
</code>
</em>
)
</code>
can be used to construct
<a class="link" href="explain-output.html#jointype_unique_subquery">
<code class="literal">
unique_subquery
</code>
</a>
or
<a class="link" href="explain-output.html#jointype_index_subquery">
<code class="literal">
index_subquery
</code>
</a>
accesses.
</p>
</li>
<li class="listitem">
<p>
Table-condition generator: If the subquery is a join of
several tables, the triggered condition is checked as soon
as possible.
</p>
</li>
</ul>
</div>
<p>
When the optimizer uses a triggered condition to create some
kind of index lookup-based access (as for the first two items
of the preceding list), it must have a fallback strategy for
the case when the condition is turned off. This fallback
strategy is always the same: Do a full table scan. In
<a class="link" href="explain.html" title="15.8.2 EXPLAIN Statement">
<code class="literal">
EXPLAIN
</code>
</a>
output, the fallback
shows up as
<code class="literal">
Full scan on NULL key
</code>
in the
<code class="literal">
Extra
</code>
column:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa88009572"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql></span> <span class="token keyword">EXPLAIN</span> <span class="token keyword">SELECT</span> t1<span class="token punctuation">.</span>col1<span class="token punctuation">,</span>
t1<span class="token punctuation">.</span>col1 <span class="token keyword">IN</span> <span class="token punctuation">(</span><span class="token keyword">SELECT</span> t2<span class="token punctuation">.</span>key1 <span class="token keyword">FROM</span> t2 <span class="token keyword">WHERE</span> t2<span class="token punctuation">.</span>col2<span class="token operator">=</span>t1<span class="token punctuation">.</span>col2<span class="token punctuation">)</span> <span class="token keyword">FROM</span> t1\G
<span class="token output"><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span> 1. row <span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span>
id<span class="token punctuation">:</span> 1
select_type<span class="token punctuation">:</span> PRIMARY
table<span class="token punctuation">:</span> t1
...
<span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span> 2. row <span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span><span class="token punctuation">*</span>
id<span class="token punctuation">:</span> 2
select_type<span class="token punctuation">:</span> DEPENDENT SUBQUERY
table<span class="token punctuation">:</span> t2
type<span class="token punctuation">:</span> index_subquery
possible_keys<span class="token punctuation">:</span> key1
key<span class="token punctuation">:</span> key1
key_len<span class="token punctuation">:</span> 5
ref<span class="token punctuation">:</span> func
rows<span class="token punctuation">:</span> 2
Extra<span class="token punctuation">:</span> Using where; Full scan on NULL key</span></code></pre>
</div>
<p>
If you run
<a class="link" href="explain.html" title="15.8.2 EXPLAIN Statement">
<code class="literal">
EXPLAIN
</code>
</a>
followed by
<a class="link" href="show-warnings.html" title="15.7.7.42 SHOW WARNINGS Statement">
<code class="literal">
SHOW WARNINGS
</code>
</a>
, you can see the
triggered condition:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-none"><div class="docs-select-all right" id="sa96538851"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-none">*************************** 1. row ***************************
Level: Note
Code: 1003
Message: select `test`.`t1`.`col1` AS `col1`,
<in_optimizer>(`test`.`t1`.`col1`,
<exists>(<index_lookup>(<cache>(`test`.`t1`.`col1`) in t2
on key1 checking NULL
where (`test`.`t2`.`col2` = `test`.`t1`.`col2`) having
trigcond(<is_not_null_test>(`test`.`t2`.`key1`))))) AS
`t1.col1 IN (select t2.key1 from t2 where t2.col2=t1.col2)`
from `test`.`t1`</code></pre>
</div>
<p>
The use of triggered conditions has some performance
implications. A
<code class="literal">
NULL IN (SELECT ...)
</code>
expression now may cause a full table scan (which is slow)
when it previously did not. This is the price paid for correct
results (the goal of the trigger-condition strategy is to
improve compliance, not speed).
</p>
<p>
For multiple-table subqueries, execution of
<code class="literal">
NULL IN
(SELECT ...)
</code>
is particularly slow because the join
optimizer does not optimize for the case where the outer
expression is
<code class="literal">
NULL
</code>
. It assumes that
subquery evaluations with
<code class="literal">
NULL
</code>
on the left
side are very rare, even if there are statistics that indicate
otherwise. On the other hand, if the outer expression might be
<code class="literal">
NULL
</code>
but never actually is, there is no
performance penalty.
</p>
<p>
To help the query optimizer better execute your queries, use
these suggestions:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
Declare a column as
<code class="literal">
NOT NULL
</code>
if it
really is. This also helps other aspects of the optimizer
by simplifying condition testing for the column.
</p>
</li>
<li class="listitem">
<p>
If you need not distinguish a
<code class="literal">
NULL
</code>
from
<code class="literal">
FALSE
</code>
subquery result, you can easily
avoid the slow execution path. Replace a comparison that
looks like this:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa42411226"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><em class="replaceable">outer_expr</em> <span class="token punctuation">[</span><span class="token operator">NOT</span><span class="token punctuation">]</span> <span class="token keyword">IN</span> <span class="token punctuation">(</span><span class="token keyword">SELECT</span> <em class="replaceable">inner_expr</em> <span class="token keyword">FROM</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">)</span></code></pre>
</div>
<p>
with this expression:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting one-line language-sql"><div class="docs-select-all right" id="sa56553508"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token punctuation">(</span><em class="replaceable">outer_expr</em> <span class="token operator">IS</span> <span class="token operator">NOT</span> <span class="token boolean">NULL</span><span class="token punctuation">)</span> <span class="token operator">AND</span> <span class="token punctuation">(</span><em class="replaceable">outer_expr</em> <span class="token punctuation">[</span><span class="token operator">NOT</span><span class="token punctuation">]</span> <span class="token keyword">IN</span> <span class="token punctuation">(</span><span class="token keyword">SELECT</span> <em class="replaceable">inner_expr</em> <span class="token keyword">FROM</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">)</span><span class="token punctuation">)</span></code></pre>
</div>
<p>
Then
<code class="literal">
NULL IN (SELECT ...)
</code>
is never
evaluated because MySQL stops evaluating
<a class="link" href="logical-operators.html#operator_and">
<code class="literal">
AND
</code>
</a>
parts as soon as the
expression result is clear.
</p>
<p>
Another possible rewrite:
</p>
<div class="copytoclipboard-wrapper">
<pre class="programlisting language-sql"><div class="docs-select-all right" id="sa18761371"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token punctuation">[</span><span class="token operator">NOT</span><span class="token punctuation">]</span> <span class="token keyword">EXISTS</span> <span class="token punctuation">(</span><span class="token keyword">SELECT</span> <em class="replaceable">inner_expr</em> <span class="token keyword">FROM</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token keyword">WHERE</span> <em class="replaceable">inner_expr</em><span class="token operator">=</span><em class="replaceable">outer_expr</em><span class="token punctuation">)</span></code></pre>
</div>
</li>
</ul>
</div>
<p>
The
<a class="link" href="switchable-optimizations.html#optflag_subquery-materialization-cost-based">
<code class="literal">
subquery_materialization_cost_based
</code>
</a>
flag of the
<a class="link" href="server-system-variables.html#sysvar_optimizer_switch">
<code class="literal">
optimizer_switch
</code>
</a>
system variable enables control over the choice between
subquery materialization and
<code class="literal">
IN
</code>
-to-
<code class="literal">
EXISTS
</code>
subquery
transformation. See
<a class="xref" href="switchable-optimizations.html" title="10.9.2 Switchable Optimizations">
Section 10.9.2, “Switchable Optimizations”
</a>
.
</p>
</div>
<br/>
</div>
|
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