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System Performance related mysql variable

Excerpted from: http://forge.mysql.com/wiki/ServerVariables

Memory-Related Variables

Memory related variables

These server variables control the amount of memory allocated to the various buffers and caches within MySQL.

The following server variables control the total amount of memory that MySQL allocates to various buffers or caches.

join_buffer_size

(PER SESSION) Controls the amount of memory allocated to perform joins on tables that have no keys which can be used to perform a condition filter.Allocated for each table joined without necessary filter conditions

(session variable) controls the total amount of memory allocated when joining on a table without an index, it can be used as a conditional filter.Assigned to each table in the join without the necessary filter conditions.

key_buffer_size

(GLOBAL) (MyISAM-only) Controls the amount of memory allocated to the MyISAM index key cache

(global variable) (MyISAM tables only) The total amount of memory allocated to the MyISAM index cache that is vacant.

innodb_buffer_pool_size

(GLOBAL) (InnoDB-only) Controls the amount of memory allocated to the InnoDB cache containing both clustered data and secondary index pages

(global variable) (Innodb only) Controls the total amount of memory allocated to the Innodb cache including cluster data and secondary index pages.

innodb_additional_mem_pool_size

(GLOBAL) (InnoDB-only) Controls the amount of memory allocated to the buffer storing the InnoDB internal data dictionary

(global variable) (Innodb only) Controls the buffer allocated to sort Innodb's internal data dictionary.

innodb_log_buffer_size

(GLOBAL) (InnoDB-only) Controls the amount of memory allocated to the buffer storing InnoDB write-ahead log entries

(global variable) (Innodb only) Controls the buffer allocated to store write-ahead log records for Innodb.

query_cache_size

(GLOBAL) Controls the amount of memory allocated to the Query Cache

(global variable) Controls the total amount of memory allocated to the query cache.

read_buffer_size

(PER SESSION) Controls the amount of memory allocated to the connecting thread in order to process a table scan

(session variable) Controls the total amount of memory allocated to the connection thread processing the scan table.

read_rnd_buffer_size

(PER SESSION) Controls the amount of memory allocated to the buffer used to read previously sorted results

(session variable) Controls the total amount of buffer allocated to read the currently sorted results.

sort_buffer_size

(PER SESSION) Controls the amount memory allocated to the buffer used to sort result sets before returning the set to the calling client

(session variable) Controls the total amount of buffering required to sort the result set before returning the result to the calling client.

thread_stack

(PER SESSION) Controls the default stack memory allocated for each connecting thread

(session variable) Controls the default total amount of stack memory allocated to each connection thread.

tmp_table_size

(GLOBAL) Controls the maximum memory to allocate to a temporary table before MySQL converts it into an on-disk MyISAM table

(global variable) Controls the maximum amount of memory required by MySQL to convert a temporary table to a MyISAM table stored on disk.

Thread-Related Variables

Thread related variables

thread_cache_size

(GLOBAL) Determines the number of thread connection objects that MySQL keeps in a cache to mitigate resource creation costs

(global variable) Determines the number of connection threads that MySQL keeps in the cache, which can reduce the system resources required to create connections.

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