Parâmetros de Performance do MySQL
Autor: Emerson | Publicado: 2013-10-22T09:42:00-07:00

Olá galera!

Essa semana discutindo com um colega desenvolvedor sobre aplicações Web, me foi questionado quais o parâmetros necessários para deixar uma aplicação Web mais rápida, tendo como base os parâmetros do Database MySQL para deixar o BD afiado para pesquisas, diversas, levando em consideração um SQL bem escrito, entre outras coisas que são importantes.Pesquisando alguns parâmetros de performance do MySQL para aplicações web, me deparei com essa tabela abaixo, que julgo muito importante &nbsp;e decidi compartilha-la para conhecimento, caso se tenha sob sua administração o MySQL

O MySQL contém diversos parâmetros para melhorar a performance do servidor e bancos de dados para aplicações Web, Móvel, etc. A planilha contem muitos parâmetros específicos para os mecanismos de armazenamento(ENGINE) que você escolher (MyIsam, InnoDB,etc) que são identificados pelo uso de ferramentas como o MySQL Administrator, phpMysqladmin e MySQL Workbench.



Parametros

Variáveis

Descrição(inglês)


Current Connections

Maximum AllowedMax_connectionsCurrently open connections as a percentage of maximum allowed connections.
Open ConnectionsThreads_connected
Connection UsageThreads_connected/ Max_connections
Currently running threadsThreads_runningHigher value indicates that you may run out of connections soon and new clients may be refused connection.
Highest no. of Concurrent ConnectionsMax_used_connections
Percentage of maximum allowed reached(Max_used_connections/ Max_connections) *100

MyISAM Key Cache

Allocated MemoryKey_buffer_sizeIf not using MyISAM tables, set it to 8-64M so as to use for internal temporary disk tables.
Block SizeKey_cache_block_size
No. of BlocksKey_buffer_size/Key_cache_block_size
Used Blocks(Key_buffer_size/ Key_cache_block_size)- key_blocks_unused
Percent of Used Blocks1-(Key_blocks_unused/No. of Blocks)*100Key cache in use.
Blocks requested from CacheKey_read_requests
Blocks served from diskKey_reads
Cache Hit Rate1- (Key_reads/Key_read_requests)*100For optimum efficiency it should be more than 99%.
Blocks Written to CacheKey_write_requests
Blocks Written to DiskKey_writes
Cache Writes RatioKey_writes/Key_write_requestsIt is generally 1 in an OLTP.

Innodb Cache

Allocated MemoryInnodb_buffer_pool_sizeIt can be 70-80% of available server memory for innodb only installations.
Cache Hit Rate1- (innodb_buffer_pool_reads/innodb_buffer_pool_read-requests) *100
Cache Write Wait RequiredInnodb_buffer_pool_wait_free/ innodb_buffer_pool_write_requestsInnodb should not have to wait before writing pages, for optimal performance.
Additional Pool SizeInnodb_additional_mem_pool_sizeStores innodb data dictionary and other internal structures.

&nbsp;Innodb Logs

Log Buffer SizeInnodb_log_buffer_size8-16 M recommended.
Log Waits RequiredInnodb_log_waits/ innodb_log_wites
No. of log filesInnodb_log_files_in_group
Size of each log fileInnodb_log_file_sizeSize of each log file in a log group.
Total size of all log filesInnodb_log_file_size * Innodb_log_files_in_groupYou should set the combined size of log files to about 25%-100% of your buffer pool size to avoid unneeded buffer pool flush activity on log file overwrite. However, note that a larger log file size will increase the time needed for the recovery process.
Total log file size as percentage to innodb buffer pool sizeTotal size of all log files/ innodb_buffer_pool_sizeIncrease the size of innodb log files to improve performance.
Log flush intervalInnodb_flush_log_at_trx_commitIf set to 1, InnoDB will flush (fsync) the transaction logs to the disk at each commit, which offers full ACID behavior. If you are willing to compromise this safety, and you are running small transactions, you may set this to 0 or 2 to reduce disk I/O to the logs. Value 0 means that the log is only written to the log file and the log file flushed to disk approximately once per second. Value 2 means the log is written to the log file at each commit, but the log file is only flushed to disk approximately once per second.

Innodb

Data PagesInnodb_buffer_pool_pages_dataThe number of pages containing data (dirty or clean).
Dirty PagesInnodb_buffer_pool_pages_dirtyThe number of pages currently dirty.
Pages FlushedInnodb_buffer_pool_pages_flushedThe number of buffer pool pages that have been requested to be flushed.
Pages FreeInnodb_buffer_pool_pages_freeThe number of free pages.
Innodb_buffer_pool_pages_latchedThe number of latched pages in InnoDB buffer pool. These are pages currently being read or written or that can’t be flushed or removed for some other reason.
Innodb_buffer_pool_pages_miscThe number of pages busy because they have been allocated for administrative overhead such as row locks or the adaptive hash index. It can also be calculated as Innodb_buffer_pool_pages_total – Innodb_buffer_pool_pages_free – Innodb_buffer_pool_pages_data.
Buffer Pool PagesInnodb_buffer_pool_pages_totalTotal size of buffer pool, in pages.
Innodb_buffer_pool_read_ahead_rndThe number of “random” read-aheads InnoDB initiated. This happens when a query is to scan a large portion of a table but in random order.
Innodb_buffer_pool_read_ahead_seqThe number of sequential read-aheads InnoDB initiated. This happens when InnoDB does a sequential full table scan.
Innodb_buffer_pool_read_requestsThe number of logical read requests InnoDB has done.
Innodb_buffer_pool_readsThe number of logical reads that InnoDB could not satisfy from buffer pool and had to do a single-page read.
Innodb_buffer_pool_wait_freeNormally, writes to the InnoDB buffer pool happen in the background. However, if it’s necessary to read or create a page and no clean pages are available, it’s necessary to wait for pages to be flushed first. This counter counts instances of these waits. If the buffer pool size was set properly, this value should be small.
Innodb_buffer_pool_write_requestsThe number writes done to the InnoDB buffer pool.
Innodb_data_fsyncsThe number of fsync() operations so far.
Innodb_data_pending_fsyncsThe current number of pending fsync() operations.
Innodb_data_pending_readsThe current number of pending reads.
Innodb_data_pending_writesThe current number of pending writes.
Innodb_data_readThe amount of data read so far, in bytes.
Innodb_data_readsThe total number of data reads.
Innodb_data_writesThe total number of data writes.
Innodb_data_writtenThe amount of data written so far, in bytes.
Innodb_log_waitsThe number of waits we had because log buffer was too small and we had to wait for it to be flushed before continuing.
Innodb_log_write_requestsThe number of log writes requests.
Innodb_log_writesThe number of physical writes to the log file.
Innodb_os_log_fsyncsThe number of fsyncs writes done to the log file.
Innodb_os_log_pending_fsyncsThe number of pending log file fsyncs.
Innodb_os_log_pending_writesPending log file writes.
Innodb_os_log_writtenThe number of bytes written to the log file.
Innodb_page_sizeThe compiled-in InnoDB page size (default 16KB). Many values are counted in pages; the page size allows them to be easily converted to bytes.
Innodb_pages_createdThe number of pages created.
Innodb_pages_readThe number of pages read.
Innodb_pages_writtenThe number of pages written.
Innodb_row_lock_current_waitsThe number of row locks currently being waited for.
Innodb_row_lock_timeThe total time spent in acquiring row locks, in milliseconds.
Innodb_row_lock_time_avgThe average time to acquire a row lock, in milliseconds.
Innodb_row_lock_time_maxThe maximum time to acquire a row lock, in milliseconds.
Innodb_row_lock_waitsThe number of times a row lock had to be waited for.
Innodb_rows_deletedThe number of rows deleted from InnoDB tables.
Innodb_rows_insertedThe number of rows inserted in InnoDB tables.
Innodb_rows_readThe number of rows read from InnoDB tables.
Innodb_rows_updatedThe number of rows updated in InnoDB tables.

&nbsp;Thread Cache

Number of threads that can be cachedThread_cache_size
Number of threads in the cacheThreads_cached
Threads created to handle connectionsThreads_created
Thread cache hit rate(Threads_created/ Threads_connected) * 100

Table Cache

No. of tables that can be cachedTable_cacheThe number of open tables for all threads. Increasing this value increases the number of file descriptors that mysqld requires.
Tables currently openOpen-tables
No. of table cache missesOpened_tablesIf the number increases rapidly, consider increasing the table_cache.

Query Cache

Query cache enabledHave_query_cache
Query Cache TypeQuery_cache_type‘Off’: query has been disabled; ‘Always’: all statements are cached except those beginning with SELECT SQL_NO_CACHE; ‘Demand’: Caching is done only for those beginning with SELECT SQL_CACHE.
Cache SizeQuery_cache_size
Max size of cached queryQuery_cache_limitThe maximum size of individual query results that can be cached.
Free MemoryQcache_free_memoryThe amount of free memory in the query cache.
Query parsing and execution bufferQuery_prealloc_sizeBetter performance by increasing this value, if you execute a lot of complex queries.
Block SizeQuery_cache_min_res_unitFor queries with large resultset, larger block size means better performance; but for queries with small resultset, a large block size leads to memory fragmentation.
Total BlocksQcache_total_blocksTotal number of blocks in the cache
Free BlocksQcache_free_blocksTotal number of free blocks in the cache
FragmentationQcache_free_blocks *100/ Qcache_total_blocksExtent of fragmentation in the query cache.
Queries in cacheQcache_queries_in_cache
Queries not cachedQcache_not_cachedQueries that cannot be cached, since it contains UDFs, user variables or it accesses system database.
Queries inserted to cacheQcache_inserts
Cache HitsQcache_hitsNumber of queries that served successfully by the query cache.
Queries pruned from cacheQcache_lowmem_prunesQueries that were inserted into the query cache, but subsequently got pruned, because of low memory.
Pruned as percentage of insertsQcache_lowmem_prunes* 100/&nbsp; Qcache_insertsIf this rate is high, consider increasing Query_cache_size system variable.
Cache Hit RateQcache_hits * 100 / (Qcache_hits + Qcache_inserts)A high rate indicates that queries in cache are being reused by other threads; a low rate shows either not enough memory allocated to query cache or identical queries are not repeatedly issued to the server.

Sort Buffers

Buffer for in-memory sortingSort_buffer_sizeIt is allocated per client, so don’t make it too large; recommended 1 M.
Temporary files created because of insufficient Sort_buffer_sizeSort_merge_passesIf this value is high, increase the value of Sort_buffer_size.
Buffer for fast rebuilds of MyISAM indexesMyisam_sort_buffer_sizeIt is allocated per client.
Buffer for reading rows in sorted order after a sort operationRead_rnd_buffer_sizeIt is allocated per client.

Table Locks

Acquired immediatelyTable_locks_immediateNumber of times table locks are acquired immediately.
Wait was neededTable_locks_waitedNumber of times a wait was required before getting a table lock. If this is high, and you have performance problems, you should first optimize your queries, and then either split your table or tables.
Lock contentionTable_locks_waited * 100 / (Table_locks_waited + Table_locks_immediate)

Full Table Scans

Number of requests to read a row based on a fixed positionhandler_read_rndThis value is high if you are doing a lot of queries that require sorting of the result. You probably have a lot of queries that require MySQL to scan entire tables or you have joins that don’t use keys properly.
Number of requests to read the next row in the data file.handler_read_rnd_nextThis value is high if you are doing a lot of table scans. Generally this suggests that your tables are not properly indexed or that your queries are not written to take advantage of the indexes you have.
Number of times the first entry was read from an indexhandler_read_firstIf this value is high, it suggests that the server is doing a lot of full index scans.
Number of requests to read the next row in key order.handler_read_nextThis value is incremented if you are querying an index column with a range constraint or if you are doing an index scan.
Number of requests to read a row based on a key.handler_read_keyIf this value is high, it is a good indication that your tables are properly indexed for your queries.
Number of requests to read the previous row in key order.handler_read_prevThis read method is mainly used to optimize ORDER BY … DESC.
Percentage of full table scans1-(handler_read_rnd_next + handler_read_rnd) / (handler_read_rnd_next + handler_read_rnd + handler_read_first + handler_read_next + handler_read_key + handler_read_prev )Ratio of the number of rows read via full table scans to the sum of all handler variables (which denotes all row accesses). A high value indicates excessive table scans. You should examine tables and queries for proper use of indexes. Turn on the slow query log, identify the queries using full table scan and tune it.
Buffer for full table scans of MyISAM tablesRead_buffer_sizeThis value is per client.
SELECTs requiring full table scanSelect_scanA high value indicates that the queries are not tuned to use indexes.
Buffer for JOINs requiring full table scanJoin_buffer_sizeThis value is per client.
Joins requiring full scan of second and subsequent tablesSelect_full_joinIf the value is high, optimize the queries to use indexes.

Temporary Tables

Maximum table sizeTmp_table_sizeThe maximum size of an internal table that can be created in memory. If an internal table is larger than this size, it is converted into a MyISAM table on disk.
Maximum size of a memory tableMax_heap_table_sizeMySQL uses the lowest value of tmp_table_size and max_heap_table_size.
Total tables createdCreated_tmp_tablesNumber of temporary tables created in memory.
Temporary tables created on diskCreated_tmp_disk_tablesIf this value is high, try increasing the values of Tmp_table_size and Max_heap_table_size.

Slow Launch Threads

Minimum launch time for a thread to be considered slowSlow_launch_time
Number of slow launch threadsSlow_launch_threadsGeneral system overload; may be caused by non-optimal queries.

Network Traffic

Bytes Received from all clientsBytes_received
Bytes Sent to all clientsByets_sent

Binary Log

Binary log enabled?Log_bin
Synchronized to disk at each write?Sync_binlogSynchronizing is the safest choice since in the event of a crash you lose at most the last transaction.
Binary log cache sizeBinlog_cache_sizeIt stores all SQL statements for the binary log during a transaction; used only with transactional engines.
Transactions that used cacheBinlog_cache_useTransactions that used the binary log cache.
Transactions that&nbsp; got saved in temporary fileBinlog_cache_disk_useNumber of transactions that used a temporary file because of insufficient Binlog_cache_size.
Percentage of transactions that&nbsp; got saved in temporary fileBinlog_cache_disk_use * 100 / Binlog_cache_use

Slow Query Log

Enabled?Log_slow_queriesIdentifies queries running slow.
Min. execution time for a query to be considered slowLong_query_time
No. of slow queriesSlow_queriesNumber of queries that took more than long_query_time to execute.

Statements

All StatementsQuestionsTotal number of statements sent to the server by all clients.
SELECTsCom_select + Qcache_hits
INSERTsCom_insert + Com_replace
UPDATEsCom_update
DELETEsCom_delete
Percentage of total Data Manipulation Statements

System

CPU Usage
Total Memory
Memory Used by MySQL
Memory Free
Memory Requirement by MySQL if max users are connectedInnodb_buffer_pool_size + Key_buffer_size + Max_connections * (sort_buffer_size + read_buffer_size + binlog_cache_size) + max_connections * 2MB


Como já viram são muitos parâmetros, próximo post trarei alguns exemplos de utilizaçao dos mesmo.


Emerson Martins

Referencias:
http://dev.mysql.com/doc/refman/5.0/en/server-parameters.html
http://www.debianhelp.co.uk/mysqlperformance.htm
http://www.slideshare.net/osscube/mysql-performance-tuning-top-10-tips
Book High-Performance-MySQL-Optimization-Replication