# myisamchk

## NAME



           myisamchk - MyISAM table-maintenance utility
    


## SYNOPSIS



    
           **myisamchk [**_options_**]**_tbl_name_ **...**
    


## DESCRIPTION



           The **myisamchk** utility gets information about your database tables
           or checks, repairs, or optimizes them.  **myisamchk** works with
           MyISAM tables (tables that have .MYD and .MYI files for storing
           data and indexes).
    
           The use of **myisamchk** with partitioned tables is not supported.
    
               **Caution**
    
               It is best to make a backup of a table before performing a
               table repair operation; under some circumstances the operation
               might cause data loss. Possible causes include but are not
               limited to file system errors.
    
           Invoke **myisamchk** like this:
    
               shell> **myisamchk [**_options_**]**_tbl_name_ **...**
    
           The _options_ specify what you want **myisamchk** to do. They are
           described in the following sections. You can also get a list of
           options by invoking **myisamchk --help**.
    
           With no options, **myisamchk** simply checks your table as the default
           operation. To get more information or to tell **myisamchk** to take
           corrective action, specify options as described in the following
           discussion.
    
           _tbl_name_ is the database table you want to check or repair. If you
           run **myisamchk** somewhere other than in the database directory, you
           must specify the path to the database directory, because **myisamchk**
           has no idea where the database is located. In fact, **myisamchk** does
           not actually care whether the files you are working on are located
           in a database directory. You can copy the files that correspond to
           a database table into some other location and perform recovery
           operations on them there.
    
           You can name several tables on the **myisamchk** command line if you
           wish. You can also specify a table by naming its index file (the
           file with the .MYI suffix). This allows you to specify all tables
           in a directory by using the pattern *.MYI. For example, if you are
           in a database directory, you can check all the MyISAM tables in
           that directory like this:
    
               shell> **myisamchk *.MYI**
    
           If you are not in the database directory, you can check all the
           tables there by specifying the path to the directory:
    
               shell> **myisamchk** _/path/to/database_dir/_***.MYI**
    
           You can even check all tables in all databases by specifying a
           wildcard with the path to the MariaDB data directory:
    
               shell> **myisamchk** _/path/to/datadir/*/*_ **.MYI**
    
           The recommended way to quickly check all MyISAM tables is:
    
               shell> **myisamchk --silent --fast** _/path/to/datadir/*/*_ **.MYI**
    
           If you want to check all MyISAM tables and repair any that are
           corrupted, you can use the following command:
    
               shell> **myisamchk --silent --force --fast --update-state \**
                         **--key_buffer_size=64M --sort_buffer_size=64M \**
                         **--read_buffer_size=1M --write_buffer_size=1M \**
                         _/path/to/datadir/*/*_ **.MYI**
    
           This command assumes that you have more than 64MB free. For more
           information about memory allocation with **myisamchk** , see the
           section called “MYISAMCHK MEMORY USAGE”.
    
               **Important**
    
               _You must ensure that no other program is using the tables_
               _while you are running_ **myisamchk**. The most effective means of
               doing so is to shut down the MariaDB server while running
               **myisamchk** , or to lock all tables that **myisamchk** is being used
               on.
    
               Otherwise, when you run **myisamchk** , it may display the
               following error message:
    
                   warning: clients are using or haven't closed the table properly
    
               This means that you are trying to check a table that has been
               updated by another program (such as the **mariadbd** server) that
               hasn't yet closed the file or that has died without closing
               the file properly, which can sometimes lead to the corruption
               of one or more MyISAM tables.
    
               If **mariadbd** is running, you must force it to flush any table
               modifications that are still buffered in memory by using FLUSH
               TABLES. You should then ensure that no one is using the tables
               while you are running **myisamchk**
    
               However, the easiest way to avoid this problem is to use CHECK
               TABLE instead of **myisamchk** to check tables.
    
           **myisamchk** supports the following options, which can be specified
           on the command line or in the [myisamchk] option file group.
    


## MYISAMCHK GENERAL OPTIONS



           The options described in this section can be used for any type of
           table maintenance operation performed by **myisamchk**. The sections
           following this one describe options that pertain only to specific
           operations, such as table checking or repairing.
    
           •   **--help** , **-?**
    
               Display a help message and exit. Options are grouped by type
               of operation.
    
           •   **--HELP** , **-H**
    
               Display a help message and exit. Options are presented in a
               single list.
    
           •   **--debug=**_debug_options_ , **-#**_debug_options_
    
               Write a debugging log. A typical _debug_options_ string is
               'd:t:o,_file_name_ '. The default is
               'd:t:o,/tmp/myisamchk.trace'.
    
           •   **--silent** , **-s**
    
               Silent mode. Write output only when errors occur. You can use
               **-s** twice (**-ss**) to make **myisamchk** very silent.
    
           •   **--verbose** , **-v**
    
               Verbose mode. Print more information about what the program
               does. This can be used with **-d** and **-e**. Use **-v** multiple times
               (**-vv** , **-vvv**) for even more output.
    
           •   **--version** , **-V**
    
               Display version information and exit.
    
           •   **--wait** , **-w**
    
               Instead of terminating with an error if the table is locked,
               wait until the table is unlocked before continuing. If you are
               running **mariadbd** with external locking disabled, the table can
               be locked only by another **myisamchk** command.
    
           •   **--print-defaults**
    
               Print the program argument list and exit.
    
           •   **--no-defaults**
    
               Don't read default options from any option file.
    
           •   **--defaults-file=#**
    
               Only read default options from the given file.
    
           •   **--defaults-extra-file=#**
    
               Read this file after the global files are read.
    
           You can also set the following variables by using **--**_var_name_**=**_value_
           syntax:
           ┌──────────────────────┬───────────────────┐
           │ **Variable** │ **Default Value** │
           ├──────────────────────┼───────────────────┤
           │ decode_bits          │ 9                 │
           ├──────────────────────┼───────────────────┤
           │ ft_max_word_len      │ version-dependent │
           ├──────────────────────┼───────────────────┤
           │ ft_min_word_len      │ 4                 │
           ├──────────────────────┼───────────────────┤
           │ ft_stopword_file     │ built-in list     │
           ├──────────────────────┼───────────────────┤
           │ key_buffer_size      │ 523264            │
           ├──────────────────────┼───────────────────┤
           │ key_cache_block_size │ 1024              │
           ├──────────────────────┼───────────────────┤
           │ myisam_block_size    │ 1024              │
           ├──────────────────────┼───────────────────┤
           │ read_buffer_size     │ 262136            │
           ├──────────────────────┼───────────────────┤
           │ sort_buffer_size     │ 2097144           │
           ├──────────────────────┼───────────────────┤
           │ sort_key_blocks      │ 16                │
           ├──────────────────────┼───────────────────┤
           │ stats_method         │ nulls_unequal     │
           ├──────────────────────┼───────────────────┤
           │ write_buffer_size    │ 262136            │
           └──────────────────────┴───────────────────┘
    
           The possible **myisamchk** variables and their default values can be
           examined with **myisamchk --help** :
    
           sort_buffer_size is used when the keys are repaired by sorting
           keys, which is the normal case when you use **--recover**.
    
           key_buffer_size is used when you are checking the table with
           **--extend-check** or when the keys are repaired by inserting keys row
           by row into the table (like when doing normal inserts). Repairing
           through the key buffer is used in the following cases:
    
           •   You use **--safe-recover**.
    
           •   The temporary files needed to sort the keys would be more than
               twice as big as when creating the key file directly. This is
               often the case when you have large key values for CHAR,
               VARCHAR, or TEXT columns, because the sort operation needs to
               store the complete key values as it proceeds. If you have lots
               of temporary space and you can force **myisamchk** to repair by
               sorting, you can use the **--sort-recover** option.
    
           Repairing through the key buffer takes much less disk space than
           using sorting, but is also much slower.
    
           If you want a faster repair, set the key_buffer_size and
           sort_buffer_size variables to about 25% of your available memory.
           You can set both variables to large values, because only one of
           them is used at a time.
    
           myisam_block_size is the size used for index blocks.
    
           stats_method influences how NULL values are treated for index
           statistics collection when the **--analyze** option is given. It acts
           like the myisam_stats_method system variable. For more
           information, see the description of myisam_stats_method in
           Section 5.1.4, “Server System Variables”, and Section 7.4.7,
           “MyISAM Index Statistics Collection”.
    
           ft_min_word_len and ft_max_word_len indicate the minimum and
           maximum word length for FULLTEXT indexes.  ft_stopword_file names
           the stopword file. These need to be set under the following
           circumstances.
    
           If you use **myisamchk** to perform an operation that modifies table
           indexes (such as repair or analyze), the FULLTEXT indexes are
           rebuilt using the default full-text parameter values for minimum
           and maximum word length and the stopword file unless you specify
           otherwise. This can result in queries failing.
    
           The problem occurs because these parameters are known only by the
           server. They are not stored in MyISAM index files. To avoid the
           problem if you have modified the minimum or maximum word length or
           the stopword file in the server, specify the same ft_min_word_len,
           ft_max_word_len, and ft_stopword_file values to **myisamchk** that you
           use for **mariadbd**. For example, if you have set the minimum word
           length to 3, you can repair a table with **myisamchk** like this:
    
               shell> **myisamchk --recover --ft_min_word_len=3** _tbl_name_**.MYI**
    
           To ensure that **myisamchk** and the server use the same values for
           full-text parameters, you can place each one in both the
           [mariadbd] and [myisamchk] sections of an option file:
    
               [mariadbd]
               ft_min_word_len=3
               [myisamchk]
               ft_min_word_len=3
    
           An alternative to using **myisamchk** is to use the REPAIR TABLE,
           ANALYZE TABLE, OPTIMIZE TABLE, or ALTER TABLE. These statements
           are performed by the server, which knows the proper full-text
           parameter values to use.
    


## MYISAMCHK CHECK OPTIONS



           **myisamchk** supports the following options for table checking
           operations:
    
           •   **--check** , **-c**
    
               Check the table for errors. This is the default operation if
               you specify no option that selects an operation type
               explicitly.
    
           •   **--check-only-changed** , **-C**
    
               Check only tables that have changed since the last check.
    
           •   **--extend-check** , **-e**
    
               Check the table very thoroughly. This is quite slow if the
               table has many indexes. This option should only be used in
               extreme cases. Normally, **myisamchk** or **myisamchk --medium-check**
               should be able to determine whether there are any errors in
               the table.
    
               If you are using **--extend-check** and have plenty of memory,
               setting the key_buffer_size variable to a large value helps
               the repair operation run faster.
    
               For a description of the output format, see the section called
               “MYISAMCHK TABLE INFORMATION”.
    
           •   **--fast** , **-F**
    
               Check only tables that haven't been closed properly.
    
           •   **--force** , **-f**
    
               Do a repair operation automatically if **myisamchk** finds any
               errors in the table. The repair type is the same as that
               specified with the **--recover** or **-r** option. States will be
               updated as with **--update-state**.
    
           •   **--information** , **-i**
    
               Print informational statistics about the table that is
               checked.
    
           •   **--medium-check** , **-m**
    
               Do a check that is faster than an **--extend-check** operation.
               This finds only 99.99% of all errors, which should be good
               enough in most cases.
    
           •   **--read-only** , **-T**
    
               Do not mark the table as checked. This is useful if you use
               **myisamchk** to check a table that is in use by some other
               application that does not use locking, such as **mariadbd** when
               run with external locking disabled.
    
           •   **--update-state** , **-U**
    
               Store information in the .MYI file to indicate when the table
               was checked and whether the table crashed. This should be used
               to get full benefit of the **--check-only-changed** option, but
               you shouldn't use this option if the **mariadbd** server is using
               the table and you are running it with external locking
               disabled.
    


## MYISAMCHK REPAIR OPTIONS



           **myisamchk** supports the following options for table repair
           operations (operations performed when an option such as **--recover**
           or **--safe-recover** is given):
    
           •   **--backup** , **-B**
    
               Make a backup of the .MYD file as _file_name_ -_time_.BAK
    
           •   **--character-sets-dir=**_path_
    
               The directory where character sets are installed.
    
           •   **--correct-checksum**
    
               Correct the checksum information for the table.
    
           •   **--create-missing-keys**
    
               Create missing keys. This assumes that the data file is
               correct and that the number of rows stored in the index file
               is correct. Enables **--quick**.
    
           •   **--data-file-length=**_len_ , **-D** _len_
    
               The maximum length of the data file (when re-creating data
               file when it is “full”).
    
           •   **--extend-check** , **-e**
    
               Do a repair that tries to recover every possible row from the
               data file. Normally, this also finds a lot of garbage rows. Do
               not use this option unless you are desperate.
    
               For a description of the output format, see the section called
               “MYISAMCHK TABLE INFORMATION”.
    
           •   **--force** , **-f**
    
               Overwrite old intermediate files (files with names like
               _tbl_name_.TMD) instead of aborting. Add another **--force** to
               avoid 'myisam_sort_buffer_size is too small' errors. In this
               case we will attempt to do the repair with the given
               **myisam_sort_buffer_size** and dynamically allocate as many
               management buffers as needed.
    
           •   **--keys-used=**_val_ , **-k** _val_
    
               For **myisamchk** , the option value is a bit-value that indicates
               which indexes to update. Each binary bit of the option value
               corresponds to a table index, where the first index is bit 0.
               An option value of 0 disables updates to all indexes, which
               can be used to get faster inserts. Deactivated indexes can be
               reactivated by using **myisamchk -r**.
    
           •   **--max-record-length=**_len_
    
               Skip rows larger than the given length if **myisamchk** cannot
               allocate memory to hold them.
    
           •   **--parallel-recover** , **-p**
    
               Use the same technique as **-r** and **-n** , but create all the keys
               in parallel, using different threads.  _This is beta-quality_
               _code. Use at your own risk!_
    
           •   **--quick** , **-q**
    
               Achieve a faster repair by modifying only the index file, not
               the data file. You can specify this option twice to force
               **myisamchk** to modify the original data file in case of
               duplicate keys. NOTE: Tables where the data file is corrupted
               can't be fixed with this option.
    
           •   **--recover** , **-r**
    
               Do a repair that can fix almost any problem except unique keys
               that are not unique (which is an extremely unlikely error with
               MyISAM tables). If you want to recover a table, this is the
               option to try first. You should try **--safe-recover** only if
               **myisamchk** reports that the table cannot be recovered using
               **--recover**. (In the unlikely case that **--recover** fails, the
               data file remains intact.)
    
               If you have lots of memory, you should increase the value of
               sort_buffer_size.
    
           •   **--safe-recover** , **-o**
    
               Do a repair using an old recovery method that reads through
               all rows in order and updates all index trees based on the
               rows found. This is an order of magnitude slower than
               **--recover** , but can handle a couple of very unlikely cases that
               **--recover** cannot. This recovery method also uses much less
               disk space than **--recover**. Normally, you should repair first
               using **--recover** , and then with **--safe-recover** only if
               **--recover** fails.
    
               If you have lots of memory, you should increase the value of
               key_buffer_size.
    
           •   **--set-collation=**_name_
    
               Specify the collation to use for sorting table indexes. The
               character set name is implied by the first part of the
               collation name.
    
           •   **--sort-recover** , **-n**
    
               Force **myisamchk** to use sorting to resolve the keys even if the
               temporary files would be very large.
    
           •   **--tmpdir=**_path_ , **-t** _path_
    
               The path of the directory to be used for storing temporary
               files. If this is not set, **myisamchk** uses the value of the
               TMPDIR environment variable.  tmpdir can be set to a list of
               directory paths that are used successively in round-robin
               fashion for creating temporary files. The separator character
               between directory names is the colon (“:”) on Unix and the
               semicolon (“;”) on Windows, NetWare, and OS/2.
    
           •   **--unpack** , **-u**
    
               Unpack a table that was packed with **myisampack**.
    


## OTHER MYISAMCHK OPTIONS



           **myisamchk** supports the following options for actions other than
           table checks and repairs:
    
           •   **--analyze** , **-a**
    
               Analyze the distribution of key values. 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. To obtain information about the key distribution,
               use a **myisamchk --description --verbose** _tbl_name_ command or
               the SHOW INDEX FROM _tbl_name_ statement.
    
           •   **--block-search=**_offset_ , **-b** _offset_
    
               Find the record that a block at the given offset belongs to.
    
           •   **--description** , **-d**
    
               Print some descriptive information about the table. Specifying
               the **--verbose** option once or twice produces additional
               information. See the section called “MYISAMCHK TABLE
               INFORMATION”.
    
           •   **--set-auto-increment[=**_value_**]** , **-A[**_value_**]**
    
               Force AUTO_INCREMENT numbering for new records to start at the
               given value (or higher, if there are existing records with
               AUTO_INCREMENT values this large). If _value_ is not specified,
               AUTO_INCREMENT numbers for new records begin with the largest
               value currently in the table, plus one.
    
           •   **--sort-index** , **-S**
    
               Sort the index tree blocks in high-low order. This optimizes
               seeks and makes table scans that use indexes faster.
    
           •   **--sort-records=**_N_ , **-R** _N_
    
               Sort records according to a particular index. This makes your
               data much more localized and may speed up range-based SELECT
               and ORDER BY operations that use this index. (The first time
               you use this option to sort a table, it may be very slow.) To
               determine a table's index numbers, use SHOW INDEX, which
               displays a table's indexes in the same order that **myisamchk**
               sees them. Indexes are numbered beginning with 1.
    
               If keys are not packed (PACK_KEYS=0), they have the same
               length, so when **myisamchk** sorts and moves records, it just
               overwrites record offsets in the index. If keys are packed
               (PACK_KEYS=1), **myisamchk** must unpack key blocks first, then
               re-create indexes and pack the key blocks again. (In this
               case, re-creating indexes is faster than updating offsets for
               each index.)
    
           •   **--stats-method=name**
    
               Specifies how index statistics collection code should treat
               NULLs. Possible values of name are "nulls_unequal" (default),
               "nulls_equal" (emulate MySQL 4 behavior), and "nulls_ignored".
    


## MYISAMCHK TABLE INFORMATION



           To obtain a description of a MyISAM table or statistics about it,
           use the commands shown here. The output from these commands is
           explained later in this section.
    
           •   **myisamchk -d** _tbl_name_
    
               Runs **myisamchk** in “describe mode” to produce a description of
               your table. If you start the MariaDB server with external
               locking disabled, **myisamchk** may report an error for a table
               that is updated while it runs. However, because **myisamchk** does
               not change the table in describe mode, there is no risk of
               destroying data.
    
           •   **myisamchk -dv** _tbl_name_
    
               Adding **-v** runs **myisamchk** in verbose mode so that it produces
               more information about the table. Adding **-v** a second time
               produces even more information.
    
           •   **myisamchk -eis** _tbl_name_
    
               Shows only the most important information from a table. This
               operation is slow because it must read the entire table.
    
           •   **myisamchk -eiv** _tbl_name_
    
               This is like **-eis** , but tells you what is being done.
    
           The _tbl_name_ argument can be either the name of a MyISAM table or
           the name of its index file, as described in myisamchk(1). Multiple
           _tbl_name_ arguments can be given.
    
           Suppose that a table named person has the following structure.
           (The MAX_ROWS table option is included so that in the example
           output from **myisamchk** shown later, some values are smaller and fit
           the output format more easily.)
    
               CREATE TABLE person
               (
                 id         INT NOT NULL AUTO_INCREMENT,
                 last_name  VARCHAR(20) NOT NULL,
                 first_name VARCHAR(20) NOT NULL,
                 birth      DATE,
                 death      DATE,
                 PRIMARY KEY (id),
                 INDEX (last_name, first_name),
                 INDEX (birth)
               ) MAX_ROWS = 1000000;
    
           Suppose also that the table has these data and index file sizes:
    
               -rw-rw----  1 mysql  mysql  9347072 Aug 19 11:47 person.MYD
               -rw-rw----  1 mysql  mysql  6066176 Aug 19 11:47 person.MYI
    
           Example of **myisamchk -dvv** output:
    
               MyISAM file:         person
               Record format:       Packed
               Character set:       latin1_swedish_ci (8)
               File-version:        1
               Creation time:       2009-08-19 16:47:41
               Recover time:        2009-08-19 16:47:56
               Status:              checked,analyzed,optimized keys
               Auto increment key:              1  Last value:                306688
               Data records:               306688  Deleted blocks:                 0
               Datafile parts:             306688  Deleted data:                   0
               Datafile pointer (bytes):        4  Keyfile pointer (bytes):        3
               Datafile length:           9347072  Keyfile length:           6066176
               Max datafile length:    4294967294  Max keyfile length:   17179868159
               Recordlength:                   54
               table description:
               Key Start Len Index   Type                 Rec/key         Root  Blocksize
               1   2     4   unique  long                       1        99328       1024
               2   6     20  multip. varchar prefix           512      3563520       1024
                   27    20          varchar                  512
               3   48    3   multip. uint24 NULL           306688      6065152       1024
               Field Start Length Nullpos Nullbit Type
               1     1     1
               2     2     4                      no zeros
               3     6     21                     varchar
               4     27    21                     varchar
               5     48    3      1       1       no zeros
               6     51    3      1       2       no zeros
    
           Explanations for the types of information **myisamchk** produces are
           given here.  “Keyfile” refers to the index file.  “Record” and
           “row” are synonymous, as are “field” and “column.”
    
           The initial part of the table description contains these values:
    
           •   MyISAM file
    
               Name of the MyISAM (index) file.
    
           •   Record format
    
               The format used to store table rows. The preceding examples
               use Fixed length. Other possible values are Compressed and
               Packed. (Packed corresponds to what SHOW TABLE STATUS reports
               as Dynamic.)
    
           •   Chararacter set
    
               The table default character set.
    
           •   File-version
    
               Version of MyISAM format. Currently always 1.
    
           •   Creation time
    
               When the data file was created.
    
           •   Recover time
    
               When the index/data file was last reconstructed.
    
           •   Status
    
               Table status flags. Possible values are crashed, open,
               changed, analyzed, optimized keys, and sorted index pages.
    
           •   Auto increment key, Last value
    
               The key number associated the table's AUTO_INCREMENT column,
               and the most recently generated value for this column. These
               fields do not appear if there is no such column.
    
           •   Data records
    
               The number of rows in the table.
    
           •   Deleted blocks
    
               How many deleted blocks still have reserved space. You can
               optimize your table to minimize this space. See Section 6.6.4,
               “MyISAM Table Optimization”.
    
           •   Datafile parts
    
               For dynamic-row format, this indicates how many data blocks
               there are. For an optimized table without fragmented rows,
               this is the same as Data records.
    
           •   Deleted data
    
               How many bytes of unreclaimed deleted data there are. You can
               optimize your table to minimize this space. See Section 6.6.4,
               “MyISAM Table Optimization”.
    
           •   Datafile pointer
    
               The size of the data file pointer, in bytes. It is usually 2,
               3, 4, or 5 bytes. Most tables manage with 2 bytes, but this
               cannot be controlled from MariaDB yet. For fixed tables, this
               is a row address. For dynamic tables, this is a byte address.
    
           •   Keyfile pointer
    
               The size of the index file pointer, in bytes. It is usually 1,
               2, or 3 bytes. Most tables manage with 2 bytes, but this is
               calculated automatically by MariaDB. It is always a block
               address.
    
           •   Max datafile length
    
               How long the table data file can become, in bytes.
    
           •   Max keyfile length
    
               How long the table index file can become, in bytes.
    
           •   Recordlength
    
               How much space each row takes, in bytes.
    
           The table description part of the output includes a list of all
           keys in the table. For each key, **myisamchk** displays some low-level
           information:
    
           •   Key
    
               This key's number. This value is shown only for the first
               column of the key. If this value is missing, the line
               corresponds to the second or later column of a multiple-column
               key. For the table shown in the example, there are two table
               description lines for the second index. This indicates that it
               is a multiple-part index with two parts.
    
           •   Start
    
               Where in the row this portion of the index starts.
    
           •   Len
    
               How long this portion of the index is. For packed numbers,
               this should always be the full length of the column. For
               strings, it may be shorter than the full length of the indexed
               column, because you can index a prefix of a string column. The
               total length of a multiple-part key is the sum of the Len
               values for all key parts.
    
           •   Index
    
               Whether a key value can exist multiple times in the index.
               Possible values are unique or multip.  (multiple).
    
           •   Type
    
               What data type this portion of the index has. This is a MyISAM
               data type with the possible values packed, stripped, or empty.
    
           •   Root
    
               Address of the root index block.
    
           •   Blocksize
    
               The size of each index block. By default this is 1024, but the
               value may be changed at compile time when MariaDB is built
               from source.
    
           •   Rec/key
    
               This is a statistical value used by the optimizer. It tells
               how many rows there are per value for this index. A unique
               index always has a value of 1. This may be updated after a
               table is loaded (or greatly changed) with **myisamchk -a**. If
               this is not updated at all, a default value of 30 is given.
    
           The last part of the output provides information about each
           column:
    
           •   Field
    
               The column number.
    
           •   Start
    
               The byte position of the column within table rows.
    
           •   Length
    
               The length of the column in bytes.
    
           •   Nullpos, Nullbit
    
               For columns that can be NULL, MyISAM stores NULL values as a
               flag in a byte. Depending on how many nullable columns there
               are, there can be one or more bytes used for this purpose. The
               Nullpos and Nullbit values, if nonempty, indicate which byte
               and bit contains that flag indicating whether the column is
               NULL.
    
               The position and number of bytes used to store NULL flags is
               shown in the line for field 1. This is why there are six Field
               lines for the person table even though it has only five
               columns.
    
           •   Type
    
               The data type. The value may contain any of the following
               descriptors:
    
               •   constant
    
                   All rows have the same value.
    
               •   no endspace
    
                   Do not store endspace.
    
               •   no endspace, not_always
    
                   Do not store endspace and do not do endspace compression
                   for all values.
    
               •   no endspace, no empty
    
                   Do not store endspace. Do not store empty values.
    
               •   table-lookup
    
                   The column was converted to an ENUM.
    
               •   zerofill(_N_)
    
                   The most significant _N_ bytes in the value are always 0 and
                   are not stored.
    
               •   no zeros
    
                   Do not store zeros.
    
               •   always zero
    
                   Zero values are stored using one bit.
    
           •   Huff tree
    
               The number of the Huffman tree associated with the column.
    
           •   Bits
    
               The number of bits used in the Huffman tree.
    
           The Huff tree and Bits fields are displayed if the table has been
           compressed with **myisampack**. See myisampack(1), for an example of
           this information.
    
           Example of **myisamchk -eiv** output:
    
               Checking MyISAM file: person
               Data records:  306688   Deleted blocks:       0
               - check file-size
               - check record delete-chain
               No recordlinks
               - check key delete-chain
               block_size 1024:
               - check index reference
               - check data record references index: 1
               Key:  1:  Keyblocks used:  98%  Packed:    0%  Max levels:  3
               - check data record references index: 2
               Key:  2:  Keyblocks used:  99%  Packed:   97%  Max levels:  3
               - check data record references index: 3
               Key:  3:  Keyblocks used:  98%  Packed:  -14%  Max levels:  3
               Total:    Keyblocks used:  98%  Packed:   89%
               - check records and index references
               _*** LOTS OF ROW NUMBERS DELETED ***_
               Records:            306688  M.recordlength:       25  Packed:            83%
               Recordspace used:       97% Empty space:           2% Blocks/Record:   1.00
               Record blocks:      306688  Delete blocks:         0
               Record data:       7934464  Deleted data:          0
               Lost space:         256512  Linkdata:        1156096
               User time 43.08, System time 1.68
               Maximum resident set size 0, Integral resident set size 0
               Non-physical pagefaults 0, Physical pagefaults 0, Swaps 0
               Blocks in 0 out 7, Messages in 0 out 0, Signals 0
               Voluntary context switches 0, Involuntary context switches 0
               Maximum memory usage: 1046926 bytes (1023k)
    
           **myisamchk -eiv** output includes the following information:
    
           •   Data records
    
               The number of rows in the table.
    
           •   Deleted blocks
    
               How many deleted blocks still have reserved space. You can
               optimize your table to minimize this space. See Section 6.6.4,
               “MyISAM Table Optimization”.
    
           •   Key
    
               The key number.
    
           •   Keyblocks used
    
               What percentage of the keyblocks are used. When a table has
               just been reorganized with **myisamchk** , the values are very high
               (very near theoretical maximum).
    
           •   Packed
    
               MariaDB tries to pack key values that have a common suffix.
               This can only be used for indexes on CHAR and VARCHAR columns.
               For long indexed strings that have similar leftmost parts,
               this can significantly reduce the space used. In the preceding
               example, the second key is 40 bytes long and a 97% reduction
               in space is achieved.
    
           •   Max levels
    
               How deep the B-tree for this key is. Large tables with long
               key values get high values.
    
           •   Records
    
               How many rows are in the table.
    
           •   M.recordlength
    
               The average row length. This is the exact row length for
               tables with fixed-length rows, because all rows have the same
               length.
    
           •   Packed
    
               MariaDB strips spaces from the end of strings. The Packed
               value indicates the percentage of savings achieved by doing
               this.
    
           •   Recordspace used
    
               What percentage of the data file is used.
    
           •   Empty space
    
               What percentage of the data file is unused.
    
           •   Blocks/Record
    
               Average number of blocks per row (that is, how many links a
               fragmented row is composed of). This is always 1.0 for
               fixed-format tables. This value should stay as close to 1.0 as
               possible. If it gets too large, you can reorganize the table.
               See Section 6.6.4, “MyISAM Table Optimization”.
    
           •   Recordblocks
    
               How many blocks (links) are used. For fixed-format tables,
               this is the same as the number of rows.
    
           •   Deleteblocks
    
               How many blocks (links) are deleted.
    
           •   Recorddata
    
               How many bytes in the data file are used.
    
           •   Deleted data
    
               How many bytes in the data file are deleted (unused).
    
           •   Lost space
    
               If a row is updated to a shorter length, some space is lost.
               This is the sum of all such losses, in bytes.
    
           •   Linkdata
    
               When the dynamic table format is used, row fragments are
               linked with pointers (4 to 7 bytes each).  Linkdata is the sum
               of the amount of storage used by all such pointers.
    


## MYISAMCHK MEMORY USAGE



           Memory allocation is important when you run **myisamchk**.  **myisamchk**
           uses no more memory than its memory-related variables are set to.
           If you are going to use **myisamchk** on very large tables, you should
           first decide how much memory you want it to use. The default is to
           use only about 3MB to perform repairs. By using larger values, you
           can get **myisamchk** to operate faster. For example, if you have more
           than 32MB RAM, you could use options such as these (in addition to
           any other options you might specify):
    
               shell> **myisamchk --sort_buffer_size=16M \**
                          **--key_buffer_size=16M \**
                          **--read_buffer_size=1M \**
                          **--write_buffer_size=1M ...**
    
           Using **--sort_buffer_size=16M** should probably be enough for most
           cases.
    
           Be aware that **myisamchk** uses temporary files in TMPDIR. If TMPDIR
           points to a memory file system, out of memory errors can easily
           occur. If this happens, run **myisamchk** with the **--tmpdir=**_path_
           option to specify a directory located on a file system that has
           more space.
    
           When performing repair operations, **myisamchk** also needs a lot of
           disk space:
    
           •   Twice the size of the data file (the original file and a
               copy). This space is not needed if you do a repair with
               **--quick** ; in this case, only the index file is re-created.
               _This space must be available on the same file system as the_
               _original data file_ , as the copy is created in the same
               directory as the original.
    
           •   Space for the new index file that replaces the old one. The
               old index file is truncated at the start of the repair
               operation, so you usually ignore this space. This space must
               be available on the same file system as the original data
               file.
    
           •   When using **--recover** or **--sort-recover**(but not when using
               **--safe-recover**), you need space on disk for sorting. This
               space is allocated in the temporary directory (specified by
               TMPDIR or **--tmpdir=**_path_). The following formula yields the
               amount of space required:
    
                   (_largest_key_ + _row_pointer_length_) × _number_of_rows_ × 2
    
               You can check the length of the keys and the
               _row_pointer_length_ with **myisamchk -dv** _tbl_name_ (see the
               section called “MYISAMCHK TABLE INFORMATION”). The
               _row_pointer_length_ and _number_of_rows_ values are the Datafile
               pointer and Data records values in the table description. To
               determine the _largest_key_ value, check the Key lines in the
               table description. The Len column indicates the number of
               bytes for each key part. For a multiple-column index, the key
               size is the sum of the Len values for all key parts.
    
           If you have a problem with disk space during repair, you can try
           **--safe-recover** instead of **--recover**.
    


* * *