MySQL 5.6 Release Notes
System variables that are true or false can be enabled at server startup by naming them, or disabled by using a
--skip-prefix. For example, to enable or disable theInnoDBadaptive hash index, you can use--innodb-adaptive-hash-indexor--skip-innodb-adaptive-hash-indexon the command line, orinnodb_adaptive_hash_indexorskip_innodb_adaptive_hash_indexin an option file.System variables that take a numeric value can be specified as
--on the command line or asvar_name=valuevar_name=valueMany system variables can be changed at runtime (see Section 5.1.8.2, “Dynamic System Variables”).
For information about
GLOBALandSESSIONvariable scope modifiers, refer to theSETstatement documentation.Certain options control the locations and layout of the
InnoDBdata files. Section 14.8.1, “InnoDB Startup Configuration” explains how to use these options.Some options, which you might not use initially, help tune
InnoDBperformance characteristics based on machine capacity and your database workload.For more information on specifying options and system variables, see Section 4.2.2, “Specifying Program Options”.
Table 14.14 InnoDB Option and Variable Reference
InnoDB Command Options
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Property Value Command-Line Format --innodb[=value]Deprecated 5.6.21 Type Enumeration Default Value ONValid Values OFFONFORCEControls loading of the
InnoDBstorage engine, if the server was compiled withInnoDBsupport. This option has a tristate format, with possible values ofOFF,ON, orFORCE. See Section 5.5.1, “Installing and Uninstalling Plugins”.To disable
InnoDB, use--innodb=OFFor--skip-innodb. In this case, because the default storage engine isInnoDB, the server does not start unless you also use--default-storage-engineand--default-tmp-storage-engineto set the default to some other engine for both permanent andTEMPORARYtables.As of MySQL 5.6.21,
--innodb=OFFand--skip-innodboptions are deprecated and their use results in a warning. These options will be removed in a future MySQL release. -
Property Value Command-Line Format --innodb-status-file[={OFF|ON}]Type Boolean Default Value OFFThe
--innodb-status-filestartup option controls whetherInnoDBcreates a file namedinnodb_status.in the data directory and writespidSHOW ENGINE INNODB STATUSoutput to it every 15 seconds, approximately.The
innodb_status.file is not created by default. To create it, start mysqld with thepid--innodb-status-fileoption.InnoDBremoves the file when the server is shut down normally. If an abnormal shutdown occurs, the status file may have to be removed manually.The
--innodb-status-fileoption is intended for temporary use, asSHOW ENGINE INNODB STATUSoutput generation can affect performance, and theinnodb_status.file can become quite large over time.pidFor related information, see Section 14.17.2, “Enabling InnoDB Monitors”.
Disable the
InnoDBstorage engine. See the description of--innodb.
InnoDB System Variables
daemon_memcached_enable_binlogProperty Value Command-Line Format --daemon-memcached-enable-binlog[={OFF|ON}]Introduced 5.6.6 System Variable daemon_memcached_enable_binlogScope Global Dynamic No Type Boolean Default Value OFFEnable this option on the master server to use the
InnoDBmemcached plugin (daemon_memcached) with the MySQL binary log. This option can only be set at server startup. You must also enable the MySQL binary log on the master server using the--log-binoption.For more information, see Section 14.20.6, “The InnoDB memcached Plugin and Replication”.
daemon_memcached_engine_lib_nameProperty Value Command-Line Format --daemon-memcached-engine-lib-name=file_nameIntroduced 5.6.6 System Variable daemon_memcached_engine_lib_nameScope Global Dynamic No Type File name Default Value innodb_engine.soSpecifies the shared library that implements the
InnoDBmemcached plugin.For more information, see Section 14.20.3, “Setting Up the InnoDB memcached Plugin”.
daemon_memcached_engine_lib_pathProperty Value Command-Line Format --daemon-memcached-engine-lib-path=dir_nameIntroduced 5.6.6 System Variable daemon_memcached_engine_lib_pathScope Global Dynamic No Type Directory name Default Value NULLThe path of the directory containing the shared library that implements the
InnoDBmemcached plugin. The default value is NULL, representing the MySQL plugin directory. You should not need to modify this parameter unless specifying amemcachedplugin for a different storage engine that is located outside of the MySQL plugin directory.For more information, see Section 14.20.3, “Setting Up the InnoDB memcached Plugin”.
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Property Value Command-Line Format --daemon-memcached-option=optionsIntroduced 5.6.6 System Variable daemon_memcached_optionScope Global Dynamic No Type String Default Value Used to pass space-separated memcached options to the underlying memcached memory object caching daemon on startup. For example, you might change the port that memcached listens on, reduce the maximum number of simultaneous connections, change the maximum memory size for a key-value pair, or enable debugging messages for the error log.
See Section 14.20.3, “Setting Up the InnoDB memcached Plugin” for usage details. For information about memcached options, refer to the memcached man page.
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Property Value Command-Line Format --daemon-memcached-r-batch-size=#Introduced 5.6.6 System Variable daemon_memcached_r_batch_sizeScope Global Dynamic No Type Integer Default Value 1Specifies how many memcached read operations (
getoperations) to perform before doing aCOMMITto start a new transaction. Counterpart ofdaemon_memcached_w_batch_size.This value is set to 1 by default, so that any changes made to the table through SQL statements are immediately visible to memcached operations. You might increase it to reduce the overhead from frequent commits on a system where the underlying table is only being accessed through the memcached interface. If you set the value too large, the amount of undo or redo data could impose some storage overhead, as with any long-running transaction.
For more information, see Section 14.20.3, “Setting Up the InnoDB memcached Plugin”.
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Property Value Command-Line Format --daemon-memcached-w-batch-size=#Introduced 5.6.6 System Variable daemon_memcached_w_batch_sizeScope Global Dynamic No Type Integer Default Value 1Specifies how many memcached write operations, such as
add,set, andincr, to perform before doing aCOMMITto start a new transaction. Counterpart ofdaemon_memcached_r_batch_size.This value is set to 1 by default, on the assumption that data being stored is important to preserve in case of an outage and should immediately be committed. When storing non-critical data, you might increase this value to reduce the overhead from frequent commits; but then the last
N-1 uncommitted write operations could be lost if a crash occurs.For more information, see Section 14.20.3, “Setting Up the InnoDB memcached Plugin”.
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Property Value Command-Line Format --ignore-builtin-innodb[={OFF|ON}]Deprecated Yes System Variable ignore_builtin_innodbScope Global Dynamic No Type Boolean In earlier versions of MySQL, enabling this variable caused the server to behave as if the built-in
InnoDBwere not present, which enabled theInnoDB Pluginto be used instead. In MySQL 5.6,InnoDBis the default storage engine andInnoDB Pluginis not used, so this variable has no effect. As of MySQL 5.6.5, it is ignored. -
Property Value Command-Line Format --innodb-adaptive-flushing[={OFF|ON}]System Variable innodb_adaptive_flushingScope Global Dynamic Yes Type Boolean Default Value ONSpecifies whether to dynamically adjust the rate of flushing dirty pages in the
InnoDBbuffer pool based on the workload. Adjusting the flush rate dynamically is intended to avoid bursts of I/O activity. This setting is enabled by default. See Section 14.8.3.4, “Configuring Buffer Pool Flushing” for more information. For general I/O tuning advice, see Section 8.5.8, “Optimizing InnoDB Disk I/O”. -
Property Value Command-Line Format --innodb-adaptive-flushing-lwm=#Introduced 5.6.6 System Variable innodb_adaptive_flushing_lwmScope Global Dynamic Yes Type Integer Default Value 10Minimum Value 0Maximum Value 70Defines the low water mark representing percentage of redo log capacity at which adaptive flushing is enabled. For more information, see Section 14.8.3.4, “Configuring Buffer Pool Flushing”.
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Property Value Command-Line Format --innodb-adaptive-hash-index[={OFF|ON}]System Variable innodb_adaptive_hash_indexScope Global Dynamic Yes Type Boolean Default Value ONWhether the
InnoDBadaptive hash index is enabled or disabled. It may be desirable, depending on your workload, to dynamically enable or disable adaptive hash indexing to improve query performance. Because the adaptive hash index may not be useful for all workloads, conduct benchmarks with it both enabled and disabled, using realistic workloads. See Section 14.5.3, “Adaptive Hash Index” for details.This variable is enabled by default. You can modify this parameter using the
SET GLOBALstatement, without restarting the server. Changing the setting at runtime requires privileges sufficient to set global system variables. See Section 5.1.8.1, “System Variable Privileges”. You can also use--skip-innodb-adaptive-hash-indexat server startup to disable it.Disabling the adaptive hash index empties the hash table immediately. Normal operations can continue while the hash table is emptied, and executing queries that were using the hash table access the index B-trees directly instead. When the adaptive hash index is re-enabled, the hash table is populated again during normal operation.
innodb_adaptive_max_sleep_delayProperty Value Command-Line Format --innodb-adaptive-max-sleep-delay=#Introduced 5.6.3 System Variable innodb_adaptive_max_sleep_delayScope Global Dynamic Yes Type Integer Default Value 150000Minimum Value 0Maximum Value 1000000Permits
InnoDBto automatically adjust the value ofinnodb_thread_sleep_delayup or down according to the current workload. Any nonzero value enables automated, dynamic adjustment of theinnodb_thread_sleep_delayvalue, up to the maximum value specified in theinnodb_adaptive_max_sleep_delayoption. The value represents the number of microseconds. This option can be useful in busy systems, with greater than 16InnoDBthreads. (In practice, it is most valuable for MySQL systems with hundreds or thousands of simultaneous connections.)For more information, see Section 14.8.5, “Configuring Thread Concurrency for InnoDB”.
innodb_additional_mem_pool_sizeProperty Value Command-Line Format --innodb-additional-mem-pool-size=#Deprecated 5.6.3 System Variable innodb_additional_mem_pool_sizeScope Global Dynamic No Type Integer Default Value 8388608Minimum Value 2097152Maximum Value 4294967295The size in bytes of a memory pool
InnoDBuses to store data dictionary information and other internal data structures. The more tables you have in your application, the more memory you allocate here. IfInnoDBruns out of memory in this pool, it starts to allocate memory from the operating system and writes warning messages to the MySQL error log. The default value is 8MB.This variable relates to the
InnoDBinternal memory allocator, which is unused ifinnodb_use_sys_mallocis enabled. For more information, see Section 14.8.4, “Configuring the Memory Allocator for InnoDB”.As of MySQL 5.6.3,
innodb_additional_mem_pool_sizeis deprecated and will be removed in a future MySQL release.-
Property Value Command-Line Format --innodb-api-bk-commit-interval=#Introduced 5.6.7 System Variable innodb_api_bk_commit_intervalScope Global Dynamic Yes Type Integer Default Value 5Minimum Value 1Maximum Value 1073741824How often to auto-commit idle connections that use the
InnoDBmemcached interface, in seconds. For more information, see Section 14.20.5.4, “Controlling Transactional Behavior of the InnoDB memcached Plugin”. -
Property Value Command-Line Format --innodb-api-disable-rowlock[={OFF|ON}]Introduced 5.6.6 System Variable innodb_api_disable_rowlockScope Global Dynamic No Type Boolean Default Value OFFUse this option to disable row locks when
InnoDBmemcached performs DML operations. By default,innodb_api_disable_rowlockis disabled, which means that memcached requests row locks forgetandsetoperations. Wheninnodb_api_disable_rowlockis enabled, memcached requests a table lock instead of row locks.innodb_api_disable_rowlockis not dynamic. It must be specified on the mysqld command line or entered in the MySQL configuration file. Configuration takes effect when the plugin is installed, which occurs when the MySQL server is started.For more information, see Section 14.20.5.4, “Controlling Transactional Behavior of the InnoDB memcached Plugin”.
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Property Value Command-Line Format --innodb-api-enable-binlog[={OFF|ON}]Introduced 5.6.6 System Variable innodb_api_enable_binlogScope Global Dynamic No Type Boolean Default Value OFFLets you use the
InnoDBmemcached plugin with the MySQL binary log. For more information, see Enabling the InnoDB memcached Binary Log. -
Property Value Command-Line Format --innodb-api-enable-mdl[={OFF|ON}]Introduced 5.6.6 System Variable innodb_api_enable_mdlScope Global Dynamic No Type Boolean Default Value OFFLocks the table used by the
InnoDBmemcached plugin, so that it cannot be dropped or altered by DDL through the SQL interface. For more information, see Section 14.20.5.4, “Controlling Transactional Behavior of the InnoDB memcached Plugin”. -
Property Value Command-Line Format --innodb-api-trx-level=#Introduced 5.6.6 System Variable innodb_api_trx_levelScope Global Dynamic Yes Type Integer Default Value 0Controls the transaction isolation level on queries processed by the memcached interface. The constants corresponding to the familiar names are:
0 =
READ UNCOMMITTED1 =
READ COMMITTED2 =
REPEATABLE READ3 =
SERIALIZABLE
For more information, see Section 14.20.5.4, “Controlling Transactional Behavior of the InnoDB memcached Plugin”.
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Property Value Command-Line Format --innodb-autoextend-increment=#System Variable innodb_autoextend_incrementScope Global Dynamic Yes Type Integer Default Value (>= 5.6.6) 64Default Value (<= 5.6.5) 8Minimum Value 1Maximum Value 1000The increment size (in megabytes) for extending the size of an auto-extending
InnoDBsystem tablespace file when it becomes full. The default value is 64. For related information, see System Tablespace Data File Configuration, and Resizing the System Tablespace.The
innodb_autoextend_incrementsetting does not affect file-per-table tablespace files. These files are auto-extending regardless of of theinnodb_autoextend_incrementsetting. The initial extensions are by small amounts, after which extensions occur in increments of 4MB. -
Property Value Command-Line Format --innodb-autoinc-lock-mode=#System Variable innodb_autoinc_lock_modeScope Global Dynamic No Type Integer Default Value 1Valid Values 012The lock mode to use for generating auto-increment values. Permissible values are 0, 1, or 2, for traditional, consecutive, or interleaved, respectively. The default setting is 1 (consecutive). For the characteristics of each lock mode, see InnoDB AUTO_INCREMENT Lock Modes.
innodb_buffer_pool_dump_at_shutdownProperty Value Command-Line Format --innodb-buffer-pool-dump-at-shutdown[={OFF|ON}]Introduced 5.6.3 System Variable innodb_buffer_pool_dump_at_shutdownScope Global Dynamic Yes Type Boolean Default Value OFFSpecifies whether to record the pages cached in the
InnoDBbuffer pool when the MySQL server is shut down, to shorten the warmup process at the next restart. Typically used in combination withinnodb_buffer_pool_load_at_startup.For more information, see Section 14.8.3.5, “Saving and Restoring the Buffer Pool State”.
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Property Value Command-Line Format --innodb-buffer-pool-dump-now[={OFF|ON}]Introduced 5.6.3 System Variable innodb_buffer_pool_dump_nowScope Global Dynamic Yes Type Boolean Default Value OFFImmediately records the pages cached in the
InnoDBbuffer pool. Typically used in combination withinnodb_buffer_pool_load_now.For more information, see Section 14.8.3.5, “Saving and Restoring the Buffer Pool State”.
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Property Value Command-Line Format --innodb-buffer-pool-filename=file_nameIntroduced 5.6.3 System Variable innodb_buffer_pool_filenameScope Global Dynamic Yes Type File name Default Value ib_buffer_poolSpecifies the name of the file that holds the list of tablespace IDs and page IDs produced by
innodb_buffer_pool_dump_at_shutdownorinnodb_buffer_pool_dump_now. Tablespace IDs and page IDs are saved in the following format:space, page_id. By default, the file is namedib_buffer_pooland is located in theInnoDBdata directory. A non-default location must be specified relative to the data directory.A file name can be specified at runtime, using a
SETstatement:SET GLOBAL innodb_buffer_pool_filename='file_name';You can also specify a file name at startup, in a startup string or MySQL configuration file. When specifying a file name at startup, the file must exist or
InnoDBwill return a startup error indicating that there is no such file or directory.For more information, see Section 14.8.3.5, “Saving and Restoring the Buffer Pool State”.
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Property Value Command-Line Format --innodb-buffer-pool-instances=#System Variable innodb_buffer_pool_instancesScope Global Dynamic No Type Integer Default Value (Other, >= 5.6.6) 8 (or 1 if innodb_buffer_pool_size < 1GBDefault Value (Windows, 32-bit platforms, >= 5.6.6) (autosized)Default Value (<= 5.6.5) 1Minimum Value 1Maximum Value 64The number of regions that the
InnoDBbuffer pool is divided into. For systems with buffer pools in the multi-gigabyte range, dividing the buffer pool into separate instances can improve concurrency, by reducing contention as different threads read and write to cached pages. Each page that is stored in or read from the buffer pool is assigned to one of the buffer pool instances randomly, using a hashing function. Each buffer pool manages its own free lists, flush lists, LRUs, and all other data structures connected to a buffer pool, and is protected by its own buffer pool mutex.This option only takes effect when setting
innodb_buffer_pool_sizeto a size of 1GB or more. The total size you specify is divided among all the buffer pools. For best efficiency, specify a combination ofinnodb_buffer_pool_instancesandinnodb_buffer_pool_sizeso that each buffer pool instance is at least 1GB.Before MySQL 5.6.6, the default is 1. The default value in MySQL 5.6.6 and higher on 32-bit Windows systems depends on the value of
innodb_buffer_pool_size, as described below:If
innodb_buffer_pool_sizeis greater than 1.3GB, the default forinnodb_buffer_pool_instancesisinnodb_buffer_pool_size/128MB, with individual memory allocation requests for each chunk. 1.3GB was chosen as the boundary at which there is significant risk for 32-bit Windows to be unable to allocate the contiguous address space needed for a single buffer pool.Otherwise, the default is 1.
On all other platforms, the default value in MySQL 5.6.6 and higher is 8 when
innodb_buffer_pool_sizeis greater than or equal to 1GB. Otherwise, the default is 1.NoteA bug in MySQL 5.6 causes
SHOW VARIABLESto report aninnodb_buffer_pool_instancesvalue of 8 wheninnodb_buffer_pool_sizeis less than 1GB and only one buffer pool instance is present (Bug #18343670). As an alternative, you can useSHOW ENGINE INNODB STATUSto check the number of buffer pool instances. If there are multiple buffer pool instances,SHOW ENGINE INNODB STATUSoutput includes anINDIVIDUAL BUFFER POOL INFOsection. -
Property Value Command-Line Format --innodb-buffer-pool-load-abort[={OFF|ON}]Introduced 5.6.3 System Variable innodb_buffer_pool_load_abortScope Global Dynamic Yes Type Boolean Default Value OFFInterrupts the process of restoring
InnoDBbuffer pool contents triggered byinnodb_buffer_pool_load_at_startuporinnodb_buffer_pool_load_now.For more information, see Section 14.8.3.5, “Saving and Restoring the Buffer Pool State”.
innodb_buffer_pool_load_at_startupProperty Value Command-Line Format --innodb-buffer-pool-load-at-startup[={OFF|ON}]Introduced 5.6.3 System Variable innodb_buffer_pool_load_at_startupScope Global Dynamic No Type Boolean Default Value OFFSpecifies that, on MySQL server startup, the
InnoDBbuffer pool is automatically warmed up by loading the same pages it held at an earlier time. Typically used in combination withinnodb_buffer_pool_dump_at_shutdown.For more information, see Section 14.8.3.5, “Saving and Restoring the Buffer Pool State”.
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Property Value Command-Line Format --innodb-buffer-pool-load-now[={OFF|ON}]Introduced 5.6.3 System Variable innodb_buffer_pool_load_nowScope Global Dynamic Yes Type Boolean Default Value OFFImmediately warms up the
InnoDBbuffer pool by loading a set of data pages, without waiting for a server restart. Can be useful to bring cache memory back to a known state during benchmarking, or to ready the MySQL server to resume its normal workload after running queries for reports or maintenance.For more information, see Section 14.8.3.5, “Saving and Restoring the Buffer Pool State”.
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Property Value Command-Line Format --innodb-buffer-pool-size=#System Variable innodb_buffer_pool_sizeScope Global Dynamic No Type Integer Default Value 134217728Minimum Value 5242880Maximum Value (64-bit platforms) 2**64-1Maximum Value (32-bit platforms) 2**32-1The size in bytes of the buffer pool, the memory area where
InnoDBcaches table and index data. The default value is 134217728 bytes (128MB). The maximum value depends on the CPU architecture; the maximum is 4294967295 (232-1) on 32-bit systems and 18446744073709551615 (264-1) on 64-bit systems. On 32-bit systems, the CPU architecture and operating system may impose a lower practical maximum size than the stated maximum. When the size of the buffer pool is greater than 1GB, settinginnodb_buffer_pool_instancesto a value greater than 1 can improve the scalability on a busy server.A larger buffer pool requires less disk I/O to access the same table data more than once. On a dedicated database server, you might set the buffer pool size to 80% of the machine's physical memory size. Be aware of the following potential issues when configuring buffer pool size, and be prepared to scale back the size of the buffer pool if necessary.
Competition for physical memory can cause paging in the operating system.
InnoDBreserves additional memory for buffers and control structures, so that the total allocated space is approximately 10% greater than the specified buffer pool size.Address space for the buffer pool must be contiguous, which can be an issue on Windows systems with DLLs that load at specific addresses.
The time to initialize the buffer pool is roughly proportional to its size. On instances with large buffer pools, initialization time might be significant. To reduce the initialization period, you can save the buffer pool state at server shutdown and restore it at server startup. See Section 14.8.3.5, “Saving and Restoring the Buffer Pool State”.
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Property Value Command-Line Format --innodb-change-buffer-max-size=#Introduced 5.6.2 System Variable innodb_change_buffer_max_sizeScope Global Dynamic Yes Type Integer Default Value 25Minimum Value 0Maximum Value 50Maximum size for the
InnoDBchange buffer, as a percentage of the total size of the buffer pool. You might increase this value for a MySQL server with heavy insert, update, and delete activity, or decrease it for a MySQL server with unchanging data used for reporting. For more information, see Section 14.5.2, “Change Buffer”. For general I/O tuning advice, see Section 8.5.8, “Optimizing InnoDB Disk I/O”. -
Property Value Command-Line Format --innodb-change-buffering=valueSystem Variable innodb_change_bufferingScope Global Dynamic Yes Type Enumeration Default Value allValid Values noneinsertsdeleteschangespurgesallWhether
InnoDBperforms change buffering, an optimization that delays write operations to secondary indexes so that the I/O operations can be performed sequentially. Permitted values are described in the following table.Table 14.15 Permitted Values for innodb_change_buffering
Value Description noneDo not buffer any operations. insertsBuffer insert operations. deletesBuffer delete marking operations; strictly speaking, the writes that mark index records for later deletion during a purge operation. changesBuffer inserts and delete-marking operations. purgesBuffer the physical deletion operations that happen in the background. allThe default. Buffer inserts, delete-marking operations, and purges. For more information, see Section 14.5.2, “Change Buffer”. For general I/O tuning advice, see Section 8.5.8, “Optimizing InnoDB Disk I/O”.
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Property Value Command-Line Format --innodb-change-buffering-debug=#System Variable innodb_change_buffering_debugScope Global Dynamic Yes Type Integer Default Value 0Maximum Value 2Sets a debug flag for
InnoDBchange buffering. A value of 1 forces all changes to the change buffer. A value of 2 causes a crash at merge. A default value of 0 indicates that the change buffering debug flag is not set. This option is only available when debugging support is compiled in using theWITH_DEBUGCMake option. -
Property Value Command-Line Format --innodb-checksum-algorithm=valueIntroduced 5.6.3 System Variable innodb_checksum_algorithmScope Global Dynamic Yes Type Enumeration Default Value (>= 5.6.7) innodbDefault Value (5.6.6) crc32Default Value (<= 5.6.5) innodbValid Values innodbcrc32nonestrict_innodbstrict_crc32strict_noneSpecifies how to generate and verify the checksum stored in the disk blocks of
InnoDBtablespaces.innodb_checksum_algorithmreplaces theinnodb_checksumsoption in MySQL 5.6.3. The following values are provided for compatibility:innodb_checksum_algorithm=innodbis the same asinnodb_checksums=ONinnodb_checksum_algorithm=noneis the same asinnodb_checksums=OFF
To avoid conflicts, remove references to
innodb_checksumsfrom MySQL configuration files and startup scripts.The value
innodbis backward-compatible with earlier versions of MySQL. The valuecrc32uses an algorithm that is faster to compute the checksum for every modified block, and to check the checksums for each disk read. It scans blocks 32 bits at a time, which is faster than theinnodbchecksum algorithm, which scans blocks 8 bits at a time. The valuenonewrites a constant value in the checksum field rather than computing a value based on the block data. The blocks in a tablespace can use a mix of old, new, and no checksum values, being updated gradually as the data is modified; once blocks in a tablespace are modified to use thecrc32algorithm, the associated tables cannot be read by earlier versions of MySQL.The strict form of a checksum algorithm reports an error if it encounters a valid but non-matching checksum value in a tablespace. It is recommended that you only use strict settings in a new instance, to set up tablespaces for the first time. Strict settings are somewhat faster, because they do not need to compute all checksum values during disk reads.
NotePrior to MySQL 5.6.25, a strict mode setting for
innodb_checksum_algorithmcausedInnoDBto halt when encountering a valid but non-matching checksum. In MySQL 5.6.25 and later, only an error message is printed, and the page is accepted as valid if it has a validinnodb,crc32ornonechecksum.The following table shows the difference between the
none,innodb, andcrc32option values, and their strict counterparts.none,innodb, andcrc32write the specified type of checksum value into each data block, but for compatibility accept other checksum values when verifying a block during a read operation. Strict settings also accept valid checksum values but print an error message when a valid non-matching checksum value is encountered. Using the strict form can make verification faster if allInnoDBdata files in an instance are created under an identicalinnodb_checksum_algorithmvalue.Table 14.16 Permitted innodb_checksum_algorithm Values
Value Generated checksum (when writing) Permitted checksums (when reading) none A constant number. Any of the checksums generated by none,innodb, orcrc32.innodb A checksum calculated in software, using the original algorithm from InnoDB.Any of the checksums generated by none,innodb, orcrc32.crc32 A checksum calculated using the crc32algorithm, possibly done with a hardware assist.Any of the checksums generated by none,innodb, orcrc32.strict_none A constant number Any of the checksums generated by none,innodb, orcrc32.InnoDBprints an error message if a valid but non-matching checksum is encountered.strict_innodb A checksum calculated in software, using the original algorithm from InnoDB.Any of the checksums generated by none,innodb, orcrc32.InnoDBprints an error message if a valid but non-matching checksum is encountered.strict_crc32 A checksum calculated using the crc32algorithm, possibly done with a hardware assist.Any of the checksums generated by none,innodb, orcrc32.InnoDBprints an error message if a valid but non-matching checksum is encountered.The default value for
innodb_checksum_algorithmwas changed frominnodbtocrc32in MySQL 5.6.6, but switched back toinnodbin 5.6.7 for backward compatibility ofInnoDBdata files, and for use with MySQL Enterprise Backup. The limitations encountered included:.ibdfiles containing CRC32 checksums could cause problems downgrading to MySQL versions prior to 5.6.3. MySQL 5.6.3 and up recognizes either the new or old checksum values for the block as correct when reading the block from disk, ensuring that data blocks are compatible during upgrade and downgrade regardless of the algorithm setting. If data written with new checksum values is processed by a version of MySQL earlier than 5.6.3, it could be reported as corrupted.Versions of MySQL Enterprise Backup up to 3.8.0 do not support backing up tablespaces that use CRC32 checksums. MySQL Enterprise Backup adds CRC32 checksum support in 3.8.1, with some limitations. Refer to the MySQL Enterprise Backup 3.8.1 Change History for more information.
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Property Value Command-Line Format --innodb-checksums[={OFF|ON}]Deprecated 5.6.3 System Variable innodb_checksumsScope Global Dynamic No Type Boolean Default Value ONInnoDBcan use checksum validation on all tablespace pages read from disk to ensure extra fault tolerance against hardware faults or corrupted data files. This validation is enabled by default. Under specialized circumstances (such as when running benchmarks) this safety feature can be disabled with--skip-innodb-checksums. You can specify the method of calculating the checksum using theinnodb_checksum_algorithmoption.In MySQL 5.6.3 and higher,
innodb_checksumsis deprecated, replaced byinnodb_checksum_algorithm.innodb_checksum_algorithm=innodbis the same asinnodb_checksums=ON(the default).innodb_checksum_algorithm=noneis the same asinnodb_checksums=OFF. Removeinnodb_checksumsoptions from your configuration files and startup scripts to avoid conflicts withinnodb_checksum_algorithm:innodb_checksums=OFFautomatically setsinnodb_checksum_algorithm=none;innodb_checksums=ONis ignored and overridden by any other setting forinnodb_checksum_algorithm. -
Property Value Command-Line Format --innodb-cmp-per-index-enabled[={OFF|ON}]Introduced 5.6.7 System Variable innodb_cmp_per_index_enabledScope Global Dynamic Yes Type Boolean Default Value OFFEnables per-index compression-related statistics in the
INFORMATION_SCHEMA.INNODB_CMP_PER_INDEXtable. Because these statistics can be expensive to gather, only enable this option on development, test, or slave instances during performance tuning related toInnoDBcompressed tables.For more information, see Section 21.30.6, “The INFORMATION_SCHEMA INNODB_CMP_PER_INDEX and INNODB_CMP_PER_INDEX_RESET Tables”, and Section 14.9.4, “Monitoring InnoDB Table Compression at Runtime”.
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Property Value Command-Line Format --innodb-commit-concurrency=#System Variable innodb_commit_concurrencyScope Global Dynamic Yes Type Integer Default Value 0Minimum Value 0Maximum Value 1000The number of threads that can commit at the same time. A value of 0 (the default) permits any number of transactions to commit simultaneously.
The value of
innodb_commit_concurrencycannot be changed at runtime from zero to nonzero or vice versa. The value can be changed from one nonzero value to another. innodb_compression_failure_threshold_pctProperty Value Command-Line Format --innodb-compression-failure-threshold-pct=#Introduced 5.6.7 System Variable innodb_compression_failure_threshold_pctScope Global Dynamic Yes Type Integer Default Value 5Minimum Value 0Maximum Value 100Defines the compression failure rate threshold for a table, as a percentage, at which point MySQL begins adding padding within compressed pages to avoid expensive compression failures. When this threshold is passed, MySQL begins to leave additional free space within each new compressed page, dynamically adjusting the amount of free space up to the percentage of page size specified by
innodb_compression_pad_pct_max. A value of zero disables the mechanism that monitors compression efficiency and dynamically adjusts the padding amount.For more information, see Section 14.9.6, “Compression for OLTP Workloads”.
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Property Value Command-Line Format --innodb-compression-level=#Introduced 5.6.7 System Variable innodb_compression_levelScope Global Dynamic Yes Type Integer Default Value 6Minimum Value 0Maximum Value 9Specifies the level of zlib compression to use for
InnoDBcompressed tables and indexes. A higher value lets you fit more data onto a storage device, at the expense of more CPU overhead during compression. A lower value lets you reduce CPU overhead when storage space is not critical, or you expect the data is not especially compressible.For more information, see Section 14.9.6, “Compression for OLTP Workloads”.
innodb_compression_pad_pct_maxProperty Value Command-Line Format --innodb-compression-pad-pct-max=#Introduced 5.6.7 System Variable innodb_compression_pad_pct_maxScope Global Dynamic Yes Type Integer Default Value 50Minimum Value 0Maximum Value 75Specifies the maximum percentage that can be reserved as free space within each compressed page, allowing room to reorganize the data and modification log within the page when a compressed table or index is updated and the data might be recompressed. Only applies when
innodb_compression_failure_threshold_pctis set to a nonzero value, and the rate of compression failures passes the cutoff point.For more information, see Section 14.9.6, “Compression for OLTP Workloads”.
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Property Value Command-Line Format --innodb-concurrency-tickets=#System Variable innodb_concurrency_ticketsScope Global Dynamic Yes Type Integer Default Value (>= 5.6.6) 5000Default Value (<= 5.6.5) 500Minimum Value 1Maximum Value 4294967295Determines the number of threads that can enter
InnoDBconcurrently. A thread is placed in a queue when it tries to enterInnoDBif the number of threads has already reached the concurrency limit. When a thread is permitted to enterInnoDB, it is given a number of “ tickets” equal to the value ofinnodb_concurrency_tickets, and the thread can enter and leaveInnoDBfreely until it has used up its tickets. After that point, the thread again becomes subject to the concurrency check (and possible queuing) the next time it tries to enterInnoDB. The default value is 5000 as of MySQL 5.6.6, 500 before that.With a small
innodb_concurrency_ticketsvalue, small transactions that only need to process a few rows compete fairly with larger transactions that process many rows. The disadvantage of a smallinnodb_concurrency_ticketsvalue is that large transactions must loop through the queue many times before they can complete, which extends the amount of time required to complete their task.With a large
innodb_concurrency_ticketsvalue, large transactions spend less time waiting for a position at the end of the queue (controlled byinnodb_thread_concurrency) and more time retrieving rows. Large transactions also require fewer trips through the queue to complete their task. The disadvantage of a largeinnodb_concurrency_ticketsvalue is that too many large transactions running at the same time can starve smaller transactions by making them wait a longer time before executing.With a nonzero
innodb_thread_concurrencyvalue, you may need to adjust theinnodb_concurrency_ticketsvalue up or down to find the optimal balance between larger and smaller transactions. TheSHOW ENGINE INNODB STATUSreport shows the number of tickets remaining for an executing transaction in its current pass through the queue. This data may also be obtained from theTRX_CONCURRENCY_TICKETScolumn of theINFORMATION_SCHEMA.INNODB_TRXtable.For more information, see Section 14.8.5, “Configuring Thread Concurrency for InnoDB”.
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Property Value Command-Line Format --innodb-data-file-path=file_nameSystem Variable innodb_data_file_pathScope Global Dynamic No Type String Default Value (>= 5.6.7) ibdata1:12M:autoextendDefault Value (<= 5.6.6) ibdata1:10M:autoextendDefines the name, size, and attributes of
InnoDBsystem tablespace data files. If you do not specify a value forinnodb_data_file_path, the default behavior is to create a single auto-extending data file, slightly larger than 12MB, namedibdata1.The full syntax for a data file specification includes the file name, file size,
autoextendattribute, andmaxattribute:file_name:file_size[:autoextend[:max:max_file_size]]File sizes are specified in kilobytes, megabytes, or gigabytes by appending
K,MorGto the size value. If specifying the data file size in kilobytes, do so in multiples of 1024. Otherwise, KB values are rounded to nearest megabyte (MB) boundary. The sum of file sizes must be, at a minimum, slightly larger than 12MB.For additional configuration information, see System Tablespace Data File Configuration. For resizing instructions, see Resizing the System Tablespace.
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Property Value Command-Line Format --innodb-data-home-dir=dir_nameSystem Variable innodb_data_home_dirScope Global Dynamic No Type Directory name The common part of the directory path for
InnoDBsystem tablespace data files. This setting does not affect the location of file-per-table tablespaces wheninnodb_file_per_tableis enabled. The default value is the MySQLdatadirectory. If you specify the value as an empty string, you can specify an absolute file paths forinnodb_data_file_path.A trailing slash is required when specifying a value for
innodb_data_home_dir. For example:[mysqld] innodb_data_home_dir = /path/to/myibdata/For related information, see Section 14.8.1, “InnoDB Startup Configuration”.
innodb_disable_sort_file_cacheProperty Value Command-Line Format --innodb-disable-sort-file-cache[={OFF|ON}]Introduced 5.6.4 System Variable innodb_disable_sort_file_cacheScope Global Dynamic Yes Type Boolean Default Value OFFDisables the operating system file system cache for merge-sort temporary files. The effect is to open such files with the equivalent of
O_DIRECT.-
Property Value Command-Line Format --innodb-doublewrite[={OFF|ON}]System Variable innodb_doublewriteScope Global Dynamic No Type Boolean Default Value ONWhen enabled (the default),
InnoDBstores all data twice, first to the doublewrite buffer, then to the actual data files. This variable can be turned off with--skip-innodb-doublewritefor benchmarks or cases when top performance is needed rather than concern for data integrity or possible failures.For related information, see Section 14.6.5, “Doublewrite Buffer”.
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Property Value Command-Line Format --innodb-fast-shutdown=#System Variable innodb_fast_shutdownScope Global Dynamic Yes Type Integer Default Value 1Valid Values 012The
InnoDBshutdown mode. If the value is 0,InnoDBdoes a slow shutdown, a full purge and a change buffer merge before shutting down. If the value is 1 (the default),InnoDBskips these operations at shutdown, a process known as a fast shutdown. If the value is 2,InnoDBflushes its logs and shuts down cold, as if MySQL had crashed; no committed transactions are lost, but the crash recovery operation makes the next startup take longer.The slow shutdown can take minutes, or even hours in extreme cases where substantial amounts of data are still buffered. Use the slow shutdown technique before upgrading or downgrading between MySQL major releases, so that all data files are fully prepared in case the upgrade process updates the file format.
Use
innodb_fast_shutdown=2in emergency or troubleshooting situations, to get the absolute fastest shutdown if data is at risk of corruption. innodb_fil_make_page_dirty_debugProperty Value Command-Line Format --innodb-fil-make-page-dirty-debug=#Introduced 5.6.17 System Variable innodb_fil_make_page_dirty_debugScope Global Dynamic Yes Type Integer Default Value 0Maximum Value 2**32-1By default, setting
innodb_fil_make_page_dirty_debugto the ID of a tablespace immediately dirties the first page of the tablespace. Ifinnodb_saved_page_number_debugis set to a non-default value, settinginnodb_fil_make_page_dirty_debugdirties the specified page. Theinnodb_fil_make_page_dirty_debugoption is only available if debugging support is compiled in using theWITH_DEBUGCMake option.-
Property Value Command-Line Format --innodb-file-format=valueSystem Variable innodb_file_formatScope Global Dynamic Yes Type String Default Value AntelopeValid Values AntelopeBarracudaEnables an
InnoDBfile format for file-per-table tablespaces. Supported file formats areAntelopeandBarracuda.Antelopeis the originalInnoDBfile format, which supportsREDUNDANTandCOMPACTrow formats forInnoDBtables.Barracudais the newer file format, which supportsCOMPRESSEDandDYNAMICrow formats.COMPRESSEDandDYNAMICrow formats enable important storage features forInnoDBtables. See Section 14.11, “InnoDB Row Formats”.To create tables that use
COMPRESSEDorDYNAMICrow format, theBarracudafile format andinnodb_file_per_tablemust be enabled.Changing the
innodb_file_formatsetting does not affect the file format of existingInnoDBtablespace files.For more information, see Section 14.10, “InnoDB File-Format Management”.
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Property Value Command-Line Format --innodb-file-format-check[={OFF|ON}]System Variable innodb_file_format_checkScope Global Dynamic No Type Boolean Default Value ONThis variable can be set to 1 or 0 at server startup to enable or disable whether
InnoDBchecks the file format tag in the system tablespace (for example,AntelopeorBarracuda). If the tag is checked and is higher than that supported by the current version ofInnoDB, an error occurs andInnoDBdoes not start. If the tag is not higher,InnoDBsets the value ofinnodb_file_format_maxto the file format tag.NoteDespite the default value sometimes being displayed as
ONorOFF, always use the numeric values 1 or 0 to turn this option on or off in your configuration file or command line string.For more information, see Section 14.10.2.1, “Compatibility Check When InnoDB Is Started”.
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Property Value Command-Line Format --innodb-file-format-max=valueSystem Variable innodb_file_format_maxScope Global Dynamic Yes Type String Default Value AntelopeValid Values AntelopeBarracudaAt server startup,
InnoDBsets the value of this variable to the file format tag in the system tablespace (for example,AntelopeorBarracuda). If the server creates or opens a table with a “higher” file format, it sets the value ofinnodb_file_format_maxto that format.For related information, see Section 14.10, “InnoDB File-Format Management”.
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Property Value Command-Line Format --innodb-file-per-table[={OFF|ON}]System Variable innodb_file_per_tableScope Global Dynamic Yes Type Boolean Default Value (>= 5.6.6) ONDefault Value (<= 5.6.5) OFFWhen
innodb_file_per_tableis enabled, tables are created in file-per-table tablespaces. When disabled, tables are created in the system tablespace. For information about file-per-table tablespaces, see Section 14.6.3.2, “File-Per-Table Tablespaces”. For information about theInnoDBsystem tablespace, see Section 14.6.3.1, “The System Tablespace”.The
innodb_file_per_tablevariable can be configured at runtime using aSET GLOBALstatement, specified on the command line at startup, or specified in an option file. Configuration at runtime requires privileges sufficient to set global system variables (see Section 5.1.8.1, “System Variable Privileges”) and immediately affects the operation of all connections.When a table that resides in a file-per-table tablespace is truncated or dropped, the freed space is returned to the operating system. Truncating or dropping a table that resides in the system tablespace only frees space in the system tablespace. Freed space in the system tablespace can be used again for
InnoDBdata but is not returned to the operating system, as system tablespace data files never shrink.When
innodb_file_per_tableis enabled, a table-copyingALTER TABLEoperation on a table that resides in the system tablespace implicitly re-creates the table in a file-per-table tablespace. To prevent this from occurring, disableinnodb_file_per_tablebefore executing table-copyingALTER TABLEoperations on tables that reside in the system tablespace. -
Property Value Command-Line Format --innodb-flush-log-at-timeout=#Introduced 5.6.6 System Variable innodb_flush_log_at_timeoutScope Global Dynamic Yes Type Integer Default Value 1Minimum Value 1Maximum Value 2700Write and flush the logs every
Nseconds.innodb_flush_log_at_timeoutallows the timeout period between flushes to be increased in order to reduce flushing and avoid impacting performance of binary log group commit. Prior to the introduction of this configuration option, flushing frequency was once per second. The default setting forinnodb_flush_log_at_timeoutis also once per second. innodb_flush_log_at_trx_commitProperty Value Command-Line Format --innodb-flush-log-at-trx-commit=#System Variable innodb_flush_log_at_trx_commitScope Global Dynamic Yes Type Enumeration Default Value 1Valid Values 012Controls the balance between strict ACID compliance for commit operations and higher performance that is possible when commit-related I/O operations are rearranged and done in batches. You can achieve better performance by changing the default value but then you can lose transactions in a crash.
The default setting of 1 is required for full ACID compliance. Logs are written and flushed to disk at each transaction commit.
With a setting of 0, logs are written and flushed to disk once per second. Transactions for which logs have not been flushed can be lost in a crash.
With a setting of 2, logs are written after each transaction commit and flushed to disk once per second. Transactions for which logs have not been flushed can be lost in a crash.
For settings 0 and 2, once-per-second flushing is not 100% guaranteed. Flushing may occur more frequently due to DDL changes and other internal
InnoDBactivities that cause logs to be flushed independently of theinnodb_flush_log_at_trx_commitsetting, and sometimes less frequently due to scheduling issues. If logs are flushed once per second, up to one second of transactions can be lost in a crash. If logs are flushed more or less frequently than once per second, the amount of transactions that can be lost varies accordingly.Log flushing frequency is controlled by
innodb_flush_log_at_timeout, which allows you to set log flushing frequency toNseconds (whereNis1 ... 2700, with a default value of 1). However, any mysqld process crash can erase up toNseconds of transactions.DDL changes and other internal
InnoDBactivities flush the log independently of theinnodb_flush_log_at_trx_commitsetting.InnoDBcrash recovery works regardless of theinnodb_flush_log_at_trx_commitsetting. Transactions are either applied entirely or erased entirely.
For durability and consistency in a replication setup that uses
InnoDBwith transactions:If binary logging is enabled, set
sync_binlog=1.Always set
innodb_flush_log_at_trx_commit=1.
CautionMany operating systems and some disk hardware fool the flush-to-disk operation. They may tell mysqld that the flush has taken place, even though it has not. In this case, the durability of transactions is not guaranteed even with the recommended settings, and in the worst case, a power outage can corrupt
InnoDBdata. Using a battery-backed disk cache in the SCSI disk controller or in the disk itself speeds up file flushes, and makes the operation safer. You can also try to disable the caching of disk writes in hardware caches.-
Property Value Command-Line Format --innodb-flush-method=valueSystem Variable innodb_flush_methodScope Global Dynamic No Type String Default Value NULLValid Values (Windows) async_unbufferednormalunbufferedValid Values (Unix, >= 5.6.7) fsyncO_DSYNClittlesyncnosyncO_DIRECTO_DIRECT_NO_FSYNCValid Values (Unix, <= 5.6.6) fsynclittlesyncnosyncO_DSYNCO_DIRECTDefines the method used to flush data to
InnoDBdata files and log files, which can affect I/O throughput.If
innodb_flush_methodis set toNULLon a Unix-like system, thefsyncoption is used by default. Ifinnodb_flush_methodis set toNULLon Windows, theasync_unbufferedoption is used by default.The
innodb_flush_methodoptions for Unix-like systems include:fsync:InnoDBuses thefsync()system call to flush both the data and log files.fsyncis the default setting.O_DSYNC:InnoDBusesO_SYNCto open and flush the log files, andfsync()to flush the data files.InnoDBdoes not useO_DSYNCdirectly because there have been problems with it on many varieties of Unix.littlesync: This option is used for internal performance testing and is currently unsupported. Use at your own risk.nosync: This option is used for internal performance testing and is currently unsupported. Use at your own risk.O_DIRECT:InnoDBusesO_DIRECT(ordirectio()on Solaris) to open the data files, and usesfsync()to flush both the data and log files. This option is available on some GNU/Linux versions, FreeBSD, and Solaris.O_DIRECT_NO_FSYNC:InnoDBusesO_DIRECTduring flushing I/O, but skips thefsync()system call after each write operation.This setting is not suitable for file systems such as XFS and EXT4, which require an
fsync()system call to synchronize file system metadata changes. If you are not sure whether your file system requires anfsync()system call to synchronize file system metadata changes, useO_DIRECTinstead.On storage devices with cache, data loss is possible if data files and redo log files reside on different storage devices, and a crash occurs before data file writes are flushed from the device cache. If you use or intend to use different storage devices for redo logs and data files, use
O_DIRECTinstead.
The
innodb_flush_methodoptions for Windows systems include:async_unbuffered:InnoDBuses Windows asynchronous I/O and non-buffered I/O.async_unbufferedis the default setting on Windows systems.Running MySQL server on a 4K sector hard drive on Windows is not supported with
async_unbuffered. The workaround is to useinnodb_flush_method=normal.normal:InnoDBuses simulated asynchronous I/O and buffered I/O. This option is used for internal performance testing and is currently unsupported. Use at your own risk.unbuffered:InnoDBuses simulated asynchronous I/O and non-buffered I/O. This option is used for internal performance testing and is currently unsupported. Use at your own risk.
How each setting affects performance depends on hardware configuration and workload. Benchmark your particular configuration to decide which setting to use, or whether to keep the default setting. Examine the
Innodb_data_fsyncsstatus variable to see the overall number offsync()calls for each setting. The mix of read and write operations in your workload can affect how a setting performs. For example, on a system with a hardware RAID controller and battery-backed write cache,O_DIRECTcan help to avoid double buffering between theInnoDBbuffer pool and the operating system file system cache. On some systems whereInnoDBdata and log files are located on a SAN, the default value orO_DSYNCmight be faster for a read-heavy workload with mostlySELECTstatements. Always test this parameter with hardware and workload that reflect your production environment. For general I/O tuning advice, see Section 8.5.8, “Optimizing InnoDB Disk I/O”. -
Property Value Command-Line Format --innodb-flush-neighbors=#Introduced 5.6.3 System Variable innodb_flush_neighborsScope Global Dynamic Yes Type Enumeration Default Value 1Valid Values 012Specifies whether flushing a page from the
InnoDBbuffer pool also flushes other dirty pages in the same extent.A setting of 0 disables
innodb_flush_neighbors. Dirty pages in the same extent are not flushed.The default setting of 1 flushes contiguous dirty pages in the same extent.
A setting of 2 flushes dirty pages in the same extent.
When the table data is stored on a traditional HDD storage device, flushing such neighbor pages in one operation reduces I/O overhead (primarily for disk seek operations) compared to flushing individual pages at different times. For table data stored on SSD, seek time is not a significant factor and you can turn this setting off to spread out write operations. For related information, see Section 14.8.3.4, “Configuring Buffer Pool Flushing”.
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Property Value Command-Line Format --innodb-flushing-avg-loops=#Introduced 5.6.6 System Variable innodb_flushing_avg_loopsScope Global Dynamic Yes Type Integer Default Value 30Minimum Value 1Maximum Value 1000Number of iterations for which
InnoDBkeeps the previously calculated snapshot of the flushing state, controlling how quickly adaptive flushing responds to changing workloads. Increasing the value makes the rate of flush operations change smoothly and gradually as the workload changes. Decreasing the value makes adaptive flushing adjust quickly to workload changes, which can cause spikes in flushing activity if the workload increases and decreases suddenly.For related information, see Section 14.8.3.4, “Configuring Buffer Pool Flushing”.
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Property Value Command-Line Format --innodb-force-load-corrupted[={OFF|ON}]Introduced 5.6.3 System Variable innodb_force_load_corruptedScope Global Dynamic No Type Boolean Default Value OFFPermits
InnoDBto load tables at startup that are marked as corrupted. Use only during troubleshooting, to recover data that is otherwise inaccessible. When troubleshooting is complete, disable this setting and restart the server. -
Property Value Command-Line Format --innodb-force-recovery=#System Variable innodb_force_recoveryScope Global Dynamic No Type Integer Default Value 0Minimum Value 0Maximum Value 6The crash recovery mode, typically only changed in serious troubleshooting situations. Possible values are from 0 to 6. For the meanings of these values and important information about
innodb_force_recovery, see Section 14.21.2, “Forcing InnoDB Recovery”.WarningOnly set this variable to a value greater than 0 in an emergency situation so that you can start
InnoDBand dump your tables. As a safety measure,InnoDBpreventsINSERT,UPDATE, orDELETEoperations wheninnodb_force_recoveryis greater than 0. As of 5.6.15, aninnodb_force_recoverysetting of 4 or greater placesInnoDBinto read-only mode.These restrictions may cause replication administration commands to fail with an error because replication settings such as
relay_log_info_repository=TABLEandmaster_info_repository=TABLEstore information inInnoDBtables. -
Property Value Introduced 5.6.4 System Variable innodb_ft_aux_tableScope Global Dynamic Yes Type String Specifies the qualified name of an
InnoDBtable containing aFULLTEXTindex. This variable is intended for diagnostic purposes and can only be set at runtime. For example:SET GLOBAL innodb_ft_aux_table = 'test/t1';After you set this variable to a name in the format
db_name/table_nameINFORMATION_SCHEMAtablesINNODB_FT_INDEX_TABLE,INNODB_FT_INDEX_CACHE,INNODB_FT_CONFIG,INNODB_FT_DELETED, andINNODB_FT_BEING_DELETEDshow information about the search index for the specified table.For more information, see Section 14.15.4, “InnoDB INFORMATION_SCHEMA FULLTEXT Index Tables”.
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Property Value Command-Line Format --innodb-ft-cache-size=#Introduced 5.6.4 System Variable innodb_ft_cache_sizeScope Global Dynamic No Type Integer Default Value (>= 5.6.10) 8000000Default Value (<= 5.6.9) 32000000Minimum Value 1600000Maximum Value 80000000The memory allocated, in bytes, for the
InnoDBFULLTEXT search index cache, which holds a parsed document in memory while creating anInnoDBFULLTEXTindex. Index inserts and updates are only committed to disk when theinnodb_ft_cache_sizesize limit is reached.innodb_ft_cache_sizedefines the cache size on a per table basis. To set a global limit for all tables, seeinnodb_ft_total_cache_size.For more information, see InnoDB Full-Text Index Cache.
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Property Value Command-Line Format --innodb-ft-enable-diag-print[={OFF|ON}]Introduced 5.6.4 System Variable innodb_ft_enable_diag_printScope Global Dynamic Yes Type Boolean Default Value (>= 5.6.7) OFFDefault Value (<= 5.6.6) ONWhether to enable additional full-text search (FTS) diagnostic output. This option is primarily intended for advanced FTS debugging and will not be of interest to most users. Output is printed to the error log and includes information such as:
FTS index sync progress (when the FTS cache limit is reached). For example:
FTS SYNC for table test, deleted count: 100 size: 10000 bytes SYNC words: 100FTS optimize progress. For example:
FTS start optimize test FTS_OPTIMIZE: optimize "mysql" FTS_OPTIMIZE: processed "mysql"FTS index build progress. For example:
Number of doc processed: 1000For FTS queries, the query parsing tree, word weight, query processing time, and memory usage are printed. For example:
FTS Search Processing time: 1 secs: 100 millisec: row(s) 10000 Full Search Memory: 245666 (bytes), Row: 10000
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Property Value Command-Line Format --innodb-ft-enable-stopword[={OFF|ON}]Introduced 5.6.4 System Variable innodb_ft_enable_stopwordScope Global, Session Dynamic Yes Type Boolean Default Value ONSpecifies that a set of stopwords is associated with an
InnoDBFULLTEXTindex at the time the index is created. If theinnodb_ft_user_stopword_tableoption is set, the stopwords are taken from that table. Else, if theinnodb_ft_server_stopword_tableoption is set, the stopwords are taken from that table. Otherwise, a built-in set of default stopwords is used.For more information, see Section 12.9.4, “Full-Text Stopwords”.
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Property Value Command-Line Format --innodb-ft-max-token-size=#Introduced 5.6.4 System Variable innodb_ft_max_token_sizeScope Global Dynamic No Type Integer Default Value 84Minimum Value 10Maximum Value (>= 5.6.14) 84Maximum Value (<= 5.6.13) 252Maximum character length of words that are stored in an
InnoDB
FULLTEXTindex. Setting a limit on this value reduces the size of the index, thus speeding up queries, by omitting long keywords or arbitrary collections of letters that are not real words and are not likely to be search terms.For more information, see Section 12.9.6, “Fine-Tuning MySQL Full-Text Search”.
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Property Value Command-Line Format --innodb-ft-min-token-size=#Introduced 5.6.4 System Variable innodb_ft_min_token_sizeScope Global Dynamic No Type Integer Default Value 3Minimum Value 0Maximum Value 16Minimum length of words that are stored in an
InnoDBFULLTEXTindex. Increasing this value reduces the size of the index, thus speeding up queries, by omitting common words that are unlikely to be significant in a search context, such as the English words “a” and “to”. For content using a CJK (Chinese, Japanese, Korean) character set, specify a value of 1.For more information, see Section 12.9.6, “Fine-Tuning MySQL Full-Text Search”.
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Property Value Command-Line Format --innodb-ft-num-word-optimize=#Introduced 5.6.4 System Variable innodb_ft_num_word_optimizeScope Global Dynamic Yes Type Integer Default Value 2000Number of words to process during each
OPTIMIZE TABLEoperation on anInnoDBFULLTEXTindex. Because a bulk insert or update operation to a table containing a full-text search index could require substantial index maintenance to incorporate all changes, you might do a series ofOPTIMIZE TABLEstatements, each picking up where the last left off.For more information, see Section 12.9.6, “Fine-Tuning MySQL Full-Text Search”.
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Property Value Command-Line Format --innodb-ft-result-cache-limit=#Introduced 5.6.13 System Variable innodb_ft_result_cache_limitScope Global Dynamic Yes Type Integer Default Value 2000000000Minimum Value 1000000Maximum Value (Windows, >= 5.6.13, <= 5.6.16) 2**32-1Maximum Value (Unix, 64-bit platforms, >= 5.6.13, <= 5.6.16) 2**64-1Maximum Value (Unix, 32-bit platforms, >= 5.6.13, <= 5.6.16) 2**32-1Maximum Value (>= 5.6.17) 2**32-1The
InnoDBfull-text search query result cache limit (defined in bytes) per full-text search query or per thread. Intermediate and finalInnoDBfull-text search query results are handled in memory. Useinnodb_ft_result_cache_limitto place a size limit on the full-text search query result cache to avoid excessive memory consumption in case of very largeInnoDBfull-text search query results (millions or hundreds of millions of rows, for example). Memory is allocated as required when a full-text search query is processed. If the result cache size limit is reached, an error is returned indicating that the query exceeds the maximum allowed memory.As of MySQL 5.6.17, the maximum value of
innodb_ft_result_cache_limitfor all platform types and bit sizes is 2**32-1. innodb_ft_server_stopword_tableProperty Value Command-Line Format --innodb-ft-server-stopword-table=db_name/table_nameIntroduced 5.6.4 System Variable innodb_ft_server_stopword_tableScope Global Dynamic Yes Type String Default Value NULLThis option is used to specify your own
InnoDBFULLTEXTindex stopword list for allInnoDBtables. To configure your own stopword list for a specificInnoDBtable, useinnodb_ft_user_stopword_table.Set
innodb_ft_server_stopword_tableto the name of the table containing a list of stopwords, in the formatdb_name/table_nameThe stopword table must exist before you configure
innodb_ft_server_stopword_table.innodb_ft_enable_stopwordmust be enabled andinnodb_ft_server_stopword_tableoption must be configured before you create theFULLTEXTindex.The stopword table must be an
InnoDBtable, containing a singleVARCHARcolumn namedvalue.For more information, see Section 12.9.4, “Full-Text Stopwords”.
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Property Value Command-Line Format --innodb-ft-sort-pll-degree=#Introduced 5.6.4 System Variable innodb_ft_sort_pll_degreeScope Global Dynamic No Type Integer Default Value 2Minimum Value 1Maximum Value 32Number of threads used in parallel to index and tokenize text in an
InnoDBFULLTEXTindex when building a search index.For related information, see Section 14.6.2.3, “InnoDB FULLTEXT Indexes”, and
innodb_sort_buffer_size. -
Property Value Command-Line Format --innodb-ft-total-cache-size=#Introduced 5.6.13 System Variable innodb_ft_total_cache_sizeScope Global Dynamic No Type Integer Default Value 640000000Minimum Value 32000000Maximum Value 1600000000The total memory allocated, in bytes, for the
InnoDBfull-text search index cache for all tables. Creating numerous tables, each with aFULLTEXTsearch index, could consume a significant portion of available memory.innodb_ft_total_cache_sizedefines a global memory limit for all full-text search indexes to help avoid excessive memory consumption. If the global limit is reached by an index operation, a forced sync is triggered.For more information, see InnoDB Full-Text Index Cache.
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Property Value Command-Line Format --innodb-ft-user-stopword-table=db_name/table_nameIntroduced 5.6.4 System Variable innodb_ft_user_stopword_tableScope Global, Session Dynamic Yes Type String Default Value NULLThis option is used to specify your own
InnoDBFULLTEXTindex stopword list on a specific table. To configure your own stopword list for allInnoDBtables, useinnodb_ft_server_stopword_table.Set
innodb_ft_user_stopword_tableto the name of the table containing a list of stopwords, in the formatdb_name/table_nameThe stopword table must exist before you configure
innodb_ft_user_stopword_table.innodb_ft_enable_stopwordmust be enabled andinnodb_ft_user_stopword_tablemust be configured before you create theFULLTEXTindex.The stopword table must be an
InnoDBtable, containing a singleVARCHARcolumn namedvalue.For more information, see Section 12.9.4, “Full-Text Stopwords”.
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Property Value Command-Line Format --innodb-io-capacity=#System Variable innodb_io_capacityScope Global Dynamic Yes Type Integer Default Value 200Minimum Value 100Maximum Value (64-bit platforms) 2**64-1Maximum Value (32-bit platforms) 2**32-1The
innodb_io_capacityvariable defines the number of I/O operations per second (IOPS) available toInnoDBbackground tasks, such as flushing pages from the buffer pool and merging data from the change buffer.For information about configuring the
innodb_io_capacityvariable, see Section 14.8.8, “Configuring InnoDB I/O Capacity”. -
Property Value Command-Line Format --innodb-io-capacity-max=#Introduced 5.6.6 System Variable innodb_io_capacity_maxScope Global Dynamic Yes Type Integer Default Value see descriptionMinimum Value 100Maximum Value (Windows, 64-bit platforms) 2**32-1Maximum Value (Unix, 64-bit platforms) 2**64-1Maximum Value (32-bit platforms) 2**32-1If flushing activity falls behind,
InnoDBcan flush more aggressively, at a higher rate of I/O operations per second (IOPS) than defined by theinnodb_io_capacityvariable. Theinnodb_io_capacity_maxvariable defines a maximum number of IOPS performed byInnoDBbackground tasks in such situations.For information about configuring the
innodb_io_capacity_maxvariable, see Section 14.8.8, “Configuring InnoDB I/O Capacity”. -
Property Value Command-Line Format --innodb-large-prefix[={OFF|ON}]Introduced 5.6.3 System Variable innodb_large_prefixScope Global Dynamic Yes Type Boolean Default Value OFFEnable this option to allow index key prefixes longer than 767 bytes (up to 3072 bytes) for
InnoDBtables that useDYNAMICorCOMPRESSEDrow format. (Creating such tables also requires the option valuesinnodb_file_format=barracudaandinnodb_file_per_table=true.) See Section 14.6.1.6, “Limits on InnoDB Tables” for maximums associated with index key prefixes under various settings.For tables that use
REDUNDANTorCOMPACTrow format, this option does not affect the permitted index key prefix length. innodb_limit_optimistic_insert_debugProperty Value Command-Line Format --innodb-limit-optimistic-insert-debug=#System Variable innodb_limit_optimistic_insert_debugScope Global Dynamic Yes Type Integer Default Value 0Minimum Value 0Maximum Value 2**32-1Limits the number of records per B-tree page. A default value of 0 means that no limit is imposed. This option is only available if debugging support is compiled in using the
WITH_DEBUGCMake option.-
Property Value Command-Line Format --innodb-lock-wait-timeout=#System Variable innodb_lock_wait_timeoutScope Global, Session Dynamic Yes Type Integer Default Value 50Minimum Value 1Maximum Value 1073741824The length of time in seconds an
InnoDBtransaction waits for a row lock before giving up. The default value is 50 seconds. A transaction that tries to access a row that is locked by anotherInnoDBtransaction waits at most this many seconds for write access to the row before issuing the following error:ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transactionWhen a lock wait timeout occurs, the current statement is rolled back (not the entire transaction). To have the entire transaction roll back, start the server with the
--innodb-rollback-on-timeoutoption. See also Section 14.21.4, “InnoDB Error Handling”.You might decrease this value for highly interactive applications or OLTP systems, to display user feedback quickly or put the update into a queue for processing later. You might increase this value for long-running back-end operations, such as a transform step in a data warehouse that waits for other large insert or update operations to finish.
innodb_lock_wait_timeoutapplies toInnoDBrow locks only. A MySQL table lock does not happen insideInnoDBand this timeout does not apply to waits for table locks.The lock wait timeout value does not apply to deadlocks, because
InnoDBdetects them immediately and rolls back one of the deadlocked transactions. See Section 14.7.5.2, “Deadlock Detection and Rollback”.innodb_lock_wait_timeoutcan be set at runtime with theSET GLOBALorSET SESSIONstatement. Changing theGLOBALsetting requires privileges sufficient to set global system variables (see Section 5.1.8.1, “System Variable Privileges”) and affects the operation of all clients that subsequently connect. Any client can change theSESSIONsetting forinnodb_lock_wait_timeout, which affects only that client. innodb_locks_unsafe_for_binlogProperty Value Command-Line Format --innodb-locks-unsafe-for-binlog[={OFF|ON}]Deprecated 5.6.3 System Variable innodb_locks_unsafe_for_binlogScope Global Dynamic No Type Boolean Default Value OFFThis variable affects how
InnoDBuses gap locking for searches and index scans.innodb_locks_unsafe_for_binlogis deprecated and will be removed in a future MySQL release.Normally,
InnoDBuses an algorithm called next-key locking that combines index-row locking with gap locking.InnoDBperforms 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, row-level locks are actually index-record locks. In addition, a next-key lock on an index record also affects the gap before the 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 recordRin an index, another session cannot insert a new index record in the gap immediately beforeRin the index order. See Section 14.7.1, “InnoDB Locking”.By default, the value of
innodb_locks_unsafe_for_binlogis 0 (disabled), which means that gap locking is enabled:InnoDBuses next-key locks for searches and index scans. To enable the variable, set it to 1. This causes gap locking to be disabled:InnoDBuses only index-record locks for searches and index scans.Enabling
innodb_locks_unsafe_for_binlogdoes not disable the use of gap locking for foreign-key constraint checking or duplicate-key checking.The effects of enabling
innodb_locks_unsafe_for_binlogare the same as setting the transaction isolation level toREAD COMMITTED, with these exceptions:Enabling
innodb_locks_unsafe_for_binlogis a global setting and affects all sessions, whereas the isolation level can be set globally for all sessions, or individually per session.innodb_locks_unsafe_for_binlogcan be set only at server startup, whereas the isolation level can be set at startup or changed at runtime.
READ COMMITTEDtherefore offers finer and more flexible control thaninnodb_locks_unsafe_for_binlog. For more information about the effect of isolation level on gap locking, see Section 14.7.2.1, “Transaction Isolation Levels”.Enabling
innodb_locks_unsafe_for_binlogmay cause phantom problems because other sessions can insert new rows into the gaps when gap locking is disabled. Suppose that there is an index on theidcolumn of thechildtable and that you want to read and lock all rows from the table having an identifier value larger than 100, with the intention of updating some column in the selected rows later:SELECT * FROM child WHERE id > 100 FOR UPDATE;The query scans the index starting from the first record where the
idis greater than 100. If the locks set on the index records in that range do not lock out inserts made in the gaps, another session can insert a new row into the table. Consequently, if you were to execute the sameSELECTagain within the same transaction, you would see a new row in the result set returned by the query. This also means that if new items are added to the database,InnoDBdoes not guarantee serializability. Therefore, ifinnodb_locks_unsafe_for_binlogis enabled,InnoDBguarantees at most an isolation level ofREAD COMMITTED. (Conflict serializability is still guaranteed.) For more information about phantoms, see Section 14.7.4, “Phantom Rows”.Enabling
innodb_locks_unsafe_for_binloghas additional effects:For
UPDATEorDELETEstatements,InnoDBholds locks only for rows that it updates or deletes. Record locks for nonmatching rows are released after MySQL has evaluated theWHEREcondition. This greatly reduces the probability of deadlocks, but they can still happen.For
UPDATEstatements, if a row is already locked,InnoDBperforms a “semi-consistent” read, returning the latest committed version to MySQL so that MySQL can determine whether the row matches theWHEREcondition of theUPDATE. If the row matches (must be updated), MySQL reads the row again and this timeInnoDBeither locks it or waits for a lock on it.
Consider the following example, beginning with this table:
CREATE TABLE t (a INT NOT NULL, b INT) ENGINE = InnoDB; INSERT INTO t VALUES (1,2),(2,3),(3,2),(4,3),(5,2); COMMIT;In this case, table has no indexes, so searches and index scans use the hidden clustered index for record locking (see Section 14.6.2.1, “Clustered and Secondary Indexes”).
Suppose that one client performs an
UPDATEusing these statements:SET autocommit = 0; UPDATE t SET b = 5 WHERE b = 3;Suppose also that a second client performs an
UPDATEby executing these statements following those of the first client:SET autocommit = 0; UPDATE t SET b = 4 WHERE b = 2;As
InnoDBexecutes eachUPDATE, it first acquires an exclusive lock for each row, and then determines whether to modify it. IfInnoDBdoes not modify the row andinnodb_locks_unsafe_for_binlogis enabled, it releases the lock. Otherwise,InnoDBretains the lock until the end of the transaction. This affects transaction processing as follows.If
innodb_locks_unsafe_for_binlogis disabled, the firstUPDATEacquires x-locks and does not release any of them:x-lock(1,2); retain x-lock x-lock(2,3); update(2,3) to (2,5); retain x-lock x-lock(3,2); retain x-lock x-lock(4,3); update(4,3) to (4,5); retain x-lock x-lock(5,2); retain x-lockThe second
UPDATEblocks as soon as it tries to acquire any locks (because the first update has retained locks on all rows), and does not proceed until the firstUPDATEcommits or rolls back:x-lock(1,2); block and wait for first UPDATE to commit or roll backIf
innodb_locks_unsafe_for_binlogis enabled, the firstUPDATEacquires x-locks and releases those for rows that it does not modify:x-lock(1,2); unlock(1,2) x-lock(2,3); update(2,3) to (2,5); retain x-lock x-lock(3,2); unlock(3,2) x-lock(4,3); update(4,3) to (4,5); retain x-lock x-lock(5,2); unlock(5,2)For the second
UPDATE,InnoDBdoes a “semi-consistent” read, returning the latest committed version of each row to MySQL so that MySQL can determine whether the row matches theWHEREcondition of theUPDATE:x-lock(1,2); update(1,2) to (1,4); retain x-lock x-lock(2,3); unlock(2,3) x-lock(3,2); update(3,2) to (3,4); retain x-lock x-lock(4,3); unlock(4,3) x-lock(5,2); update(5,2) to (5,4); retain x-lock-
Property Value Command-Line Format --innodb-log-buffer-size=#System Variable innodb_log_buffer_sizeScope Global Dynamic No Type Integer Default Value 8388608Minimum Value 262144Maximum Value 4294967295The size in bytes of the buffer that
InnoDBuses to write to the log files on disk. The default value is 8MB. A large log buffer enables large transactions to run without the need to write the log to disk before the transactions commit. Thus, if you have transactions that update, insert, or delete many rows, making the log buffer larger saves disk I/O. For related information, see Memory Configuration, and Section 8.5.4, “Optimizing InnoDB Redo Logging”. For general I/O tuning advice, see Section 8.5.8, “Optimizing InnoDB Disk I/O”. -
Property Value Command-Line Format --innodb-log-checkpoint-now[={OFF|ON}]Introduced 5.6.12 System Variable innodb_log_checkpoint_nowScope Global Dynamic Yes Type Boolean Default Value OFFEnable this debug option to force
InnoDBto write a checkpoint. This option is only available if debugging support is compiled in using theWITH_DEBUGCMake option. -
Property Value Command-Line Format --innodb-log-compressed-pages[={OFF|ON}]Introduced 5.6.11 System Variable innodb_log_compressed_pagesScope Global Dynamic Yes Type Boolean Default Value ONSpecifies whether images of re-compressed pages are written to the redo log. Re-compression may occur when changes are made to compressed data.
innodb_log_compressed_pagesis enabled by default to prevent corruption that could occur if a different version of thezlibcompression algorithm is used during recovery. If you are certain that thezlibversion will not change, you can disableinnodb_log_compressed_pagesto reduce redo log generation for workloads that modify compressed data.To measure the effect of enabling or disabling
innodb_log_compressed_pages, compare redo log generation for both settings under the same workload. Options for measuring redo log generation include observing theLog sequence number(LSN) in theLOGsection ofSHOW ENGINE INNODB STATUSoutput, or monitoringInnodb_os_log_writtenstatus for the number of bytes written to the redo log files.For related information, see Section 14.9.6, “Compression for OLTP Workloads”.
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Property Value Command-Line Format --innodb-log-file-size=#System Variable innodb_log_file_sizeScope Global Dynamic No Type Integer Default Value (>= 5.6.8) 50331648Default Value (<= 5.6.7) 5242880Minimum Value 1048576Maximum Value (>= 5.6.3) 512GB / innodb_log_files_in_groupMaximum Value (<= 5.6.2) 4GB / innodb_log_files_in_groupThe size in bytes of each log file in a log group. The combined size of log files (
innodb_log_file_size*innodb_log_files_in_group) cannot exceed a maximum value that is slightly less than 512GB. A pair of 255 GB log files, for example, approaches the limit but does not exceed it. The default value is 48MB.Generally, the combined size of the log files should be large enough that the server can smooth out peaks and troughs in workload activity, which often means that there is enough redo log space to handle more than an hour of write activity. The larger the value, the less checkpoint flush activity is required in the buffer pool, saving disk I/O. Larger log files also make crash recovery slower, although improvements to recovery performance make log file size less of a consideration than it was in earlier versions of MySQL.
ImportantDue to Bug #69477, redo log writes for large, externally stored
BLOBfields could overwrite the most recent checkpoint. To address this bug, a patch introduced in MySQL 5.6.20 limits the size of redo logBLOBwrites to 10% of the redo log file size. As a result of this limit,innodb_log_file_sizeshould be set to a value greater than 10 times the largestBLOBdata size found in the rows of your tables plus the length of other variable length fields (VARCHAR,VARBINARY, andTEXTtype fields).In MySQL 5.6.22, the redo log
BLOBwrite limit is relaxed to 10% of the total redo log size (innodb_log_file_size*innodb_log_files_in_group). (Bug #19498877)For related information, see Redo Log File Configuration. For general I/O tuning advice, see Section 8.5.8, “Optimizing InnoDB Disk I/O”.
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Property Value Command-Line Format --innodb-log-files-in-group=#System Variable innodb_log_files_in_groupScope Global Dynamic No Type Integer Default Value 2Minimum Value 2Maximum Value 100The number of log files in the log group.
InnoDBwrites to the files in a circular fashion. The default (and recommended) value is 2. The location of the files is specified byinnodb_log_group_home_dir. The combined size of log files (innodb_log_file_size*innodb_log_files_in_group) can be up to 512GB.For related information, see Redo Log File Configuration.
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Property Value Command-Line Format --innodb-log-group-home-dir=dir_nameSystem Variable innodb_log_group_home_dirScope Global Dynamic No Type Directory name The directory path to the
InnoDBredo log files, whose number is specified byinnodb_log_files_in_group. If you do not specify anyInnoDBlog variables, the default is to create two files namedib_logfile0andib_logfile1in the MySQL data directory. Log file size is given by theinnodb_log_file_sizesystem variable.For related information, see Redo Log File Configuration.
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Property Value Command-Line Format --innodb-lru-scan-depth=#Introduced 5.6.3 System Variable innodb_lru_scan_depthScope Global Dynamic Yes Type Integer Default Value 1024Minimum Value 100Maximum Value (64-bit platforms) 2**64-1Maximum Value (32-bit platforms) 2**32-1A parameter that influences the algorithms and heuristics for the flush operation for the
InnoDBbuffer pool. Primarily of interest to performance experts tuning I/O-intensive workloads. It specifies, per buffer pool instance, how far down the buffer pool LRU page list the page cleaner thread scans looking for dirty pages to flush. This is a background operation performed once per second.A setting smaller than the default is generally suitable for most workloads. A value that is much higher than necessary may impact performance. Only consider increasing the value if you have spare I/O capacity under a typical workload. Conversely, if a write-intensive workload saturates your I/O capacity, decrease the value, especially in the case of a large buffer pool.
When tuning
innodb_lru_scan_depth, start with a low value and configure the setting upward with the goal of rarely seeing zero free pages. Also, consider adjustinginnodb_lru_scan_depthwhen changing the number of buffer pool instances, sinceinnodb_lru_scan_depth*innodb_buffer_pool_instancesdefines the amount of work performed by the page cleaner thread each second.For related information, see Section 14.8.3.4, “Configuring Buffer Pool Flushing”. For general I/O tuning advice, see Section 8.5.8, “Optimizing InnoDB Disk I/O”.
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Property Value Command-Line Format --innodb-max-dirty-pages-pct=#System Variable innodb_max_dirty_pages_pctScope Global Dynamic Yes Type Numeric Default Value 75Minimum Value 0Maximum Value 99InnoDBtries to flush data from the buffer pool so that the percentage of dirty pages does not exceed this value. Specify an integer in the range from 0 to 99. The default value is 75.The
innodb_max_dirty_pages_pctsetting establishes a target for flushing activity. It does not affect the rate of flushing. For information about managing the rate of flushing, see Section 14.8.3.4, “Configuring Buffer Pool Flushing”.For related information, see Section 14.8.3.4, “Configuring Buffer Pool Flushing”. For general I/O tuning advice, see Section 8.5.8, “Optimizing InnoDB Disk I/O”.
innodb_max_dirty_pages_pct_lwmProperty Value Command-Line Format --innodb-max-dirty-pages-pct-lwm=#Introduced 5.6.6 System Variable innodb_max_dirty_pages_pct_lwmScope Global Dynamic Yes Type Numeric Default Value 0Minimum Value 0Maximum Value 99Defines a low water mark representing the percentage of dirty pages at which preflushing is enabled to control the dirty page ratio. The default of 0 disables the pre-flushing behavior entirely. For more information, see Section 14.8.3.4, “Configuring Buffer Pool Flushing”.
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Property Value Command-Line Format --innodb-max-purge-lag=#System Variable innodb_max_purge_lagScope Global Dynamic Yes Type Integer Default Value 0Minimum Value 0Maximum Value 4294967295Defines the desired maximum purge lag. If this value is exceeded, a delay is imposed on
INSERT,UPDATE, andDELETEoperations to allow time for purge to catch up. The default value is 0, which means there is no maximum purge lag and no delay.For more information, see Section 14.8.10, “Purge Configuration”.
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Property Value Command-Line Format --innodb-max-purge-lag-delay=#Introduced 5.6.5 System Variable innodb_max_purge_lag_delayScope Global Dynamic Yes Type Integer Default Value 0Minimum Value 0Specifies the maximum delay in microseconds for the delay imposed when the
innodb_max_purge_lagthreshold is exceeded. The specifiedinnodb_max_purge_lag_delayvalue is an upper limit on the delay period calculated by theinnodb_max_purge_lagformula.For more information, see Section 14.8.10, “Purge Configuration”.
Has no effect. This variable is deprecated as of MySQL 5.6.11 and will be removed in a future MySQL release.
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Property Value Command-Line Format --innodb-monitor-disable={counter|module|pattern|all}Introduced 5.6.2 System Variable innodb_monitor_disableScope Global Dynamic Yes Type String Disables
InnoDBmetrics counters. Counter data may be queried using theINFORMATION_SCHEMA.INNODB_METRICStable. For usage information, see Section 14.15.6, “InnoDB INFORMATION_SCHEMA Metrics Table”. -
Property Value Command-Line Format --innodb-monitor-enable={counter|module|pattern|all}Introduced 5.6.2 System Variable innodb_monitor_enableScope Global Dynamic Yes Type String Enables
InnoDBmetrics counters. Counter data may be queried using theINFORMATION_SCHEMA.INNODB_METRICStable. For usage information, see Section 14.15.6, “InnoDB INFORMATION_SCHEMA Metrics Table”. -
Property Value Command-Line Format --innodb-monitor-reset={counter|module|pattern|all}Introduced 5.6.2 System Variable innodb_monitor_resetScope Global Dynamic Yes Type Enumeration Default Value empty stringValid Values countermodulepatternallResets the count value for
InnoDBmetrics counters to zero. Counter data may be queried using theINFORMATION_SCHEMA.INNODB_METRICStable. For usage information, see Section 14.15.6, “InnoDB INFORMATION_SCHEMA Metrics Table”. -
Property Value Command-Line Format --innodb-monitor-reset-all={counter|module|pattern|all}Introduced 5.6.2 System Variable innodb_monitor_reset_allScope Global Dynamic Yes Type Enumeration Default Value empty stringValid Values countermodulepatternallResets all values (minimum, maximum, and so on) for
InnoDBmetrics counters. Counter data may be queried using theINFORMATION_SCHEMA.INNODB_METRICStable. For usage information, see Section 14.15.6, “InnoDB INFORMATION_SCHEMA Metrics Table”. -
Property Value Command-Line Format --innodb-numa-interleave[={OFF|ON}]Introduced 5.6.27 System Variable innodb_numa_interleaveScope Global Dynamic No Type Boolean Default Value OFFEnables the NUMA interleave memory policy for allocation of the
InnoDBbuffer pool. Wheninnodb_numa_interleaveis enabled, the NUMA memory policy is set toMPOL_INTERLEAVEfor the mysqld process. After theInnoDBbuffer pool is allocated, the NUMA memory policy is set back toMPOL_DEFAULT. For theinnodb_numa_interleaveoption to be available, MySQL must be compiled on a NUMA-enabled Linux system. -
Property Value Command-Line Format --innodb-old-blocks-pct=#System Variable innodb_old_blocks_pctScope Global Dynamic Yes Type Integer Default Value 37Minimum Value 5Maximum Value 95Specifies the approximate percentage of the
InnoDBbuffer pool used for the old block sublist. The range of values is 5 to 95. The default value is 37 (that is, 3/8 of the pool). Often used in combination withinnodb_old_blocks_time.For more information, see Section 14.8.3.2, “Making the Buffer Pool Scan Resistant”. For information about buffer pool management, the LRU algorithm, and eviction policies, see Section 14.5.1, “Buffer Pool”.
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Property Value Command-Line Format --innodb-old-blocks-time=#System Variable innodb_old_blocks_timeScope Global Dynamic Yes Type Integer Default Value (>= 5.6.6) 1000Default Value (<= 5.6.5) 0Minimum Value 0Maximum Value 2**32-1Non-zero values protect against the buffer pool being filled by data that is referenced only for a brief period, such as during a full table scan. Increasing this value offers more protection against full table scans interfering with data cached in the buffer pool.
Specifies how long in milliseconds a block inserted into the old sublist must stay there after its first access before it can be moved to the new sublist. If the value is 0, a block inserted into the old sublist moves immediately to the new sublist the first time it is accessed, no matter how soon after insertion the access occurs. If the value is greater than 0, blocks remain in the old sublist until an access occurs at least that many milliseconds after the first access. For example, a value of 1000 causes blocks to stay in the old sublist for 1 second after the first access before they become eligible to move to the new sublist.
The default value is 1000 as of MySQL 5.6.6, 0 before that.
This variable is often used in combination with
innodb_old_blocks_pct. For more information, see Section 14.8.3.2, “Making the Buffer Pool Scan Resistant”. For information about buffer pool management, the LRU algorithm, and eviction policies, see Section 14.5.1, “Buffer Pool”. innodb_online_alter_log_max_sizeProperty Value Command-Line Format --innodb-online-alter-log-max-size=#Introduced 5.6.6 System Variable innodb_online_alter_log_max_sizeScope Global Dynamic Yes Type Integer Default Value 134217728Minimum Value 65536Maximum Value 2**64-1Specifies an upper limit in bytes on the size of the temporary log files used during online DDL operations for
InnoDBtables. There is one such log file for each index being created or table being altered. This log file stores data inserted, updated, or deleted in the table during the DDL operation. The temporary log file is extended when needed by the value ofinnodb_sort_buffer_size, up to the maximum specified byinnodb_online_alter_log_max_size. If a temporary log file exceeds the upper size limit, theALTER TABLEoperation fails and all uncommitted concurrent DML operations are rolled back. Thus, a large value for this option allows more DML to happen during an online DDL operation, but also extends the period of time at the end of the DDL operation when the table is locked to apply the data from the log.-
Property Value Command-Line Format --innodb-open-files=#System Variable innodb_open_filesScope Global Dynamic No Type Integer Default Value (>= 5.6.6) -1(signifies autosizing; do not assign this literal value)Default Value (<= 5.6.5) 300Minimum Value 10Maximum Value 4294967295This variable is only relevant if you use multiple
InnoDBtablespaces. It specifies the maximum number of.ibdfiles that MySQL can keep open at one time. The minimum value is 10. As of MySQL 5.6.6, the default value is 300 ifinnodb_file_per_tableis not enabled, and the higher of 300 andtable_open_cacheotherwise. Before 5.6.6, the default value is 300.The file descriptors used for
.ibdfiles are forInnoDBtables only. They are independent of those specified by theopen_files_limitsystem variable, and do not affect the operation of the table cache. For general I/O tuning advice, see Section 8.5.8, “Optimizing InnoDB Disk I/O”. -
Property Value Command-Line Format --innodb-optimize-fulltext-only[={OFF|ON}]Introduced 5.6.4 System Variable innodb_optimize_fulltext_onlyScope Global Dynamic Yes Type Boolean Default Value OFFChanges the way
OPTIMIZE TABLEoperates onInnoDBtables. Intended to be enabled temporarily, during maintenance operations forInnoDBtables withFULLTEXTindexes.By default,
OPTIMIZE TABLEreorganizes data in the clustered index of the table. When this option is enabled,OPTIMIZE TABLEskips the reorganization of table data, and instead processes newly added, deleted, and updated token data forInnoDBFULLTEXTindexes. For more information, see Optimizing InnoDB Full-Text Indexes. -
Property Value Command-Line Format --innodb-page-size=#Introduced 5.6.4 System Variable innodb_page_sizeScope Global Dynamic No Type Enumeration Default Value 16384Valid Values 4096819216384Specifies the page size for
InnoDBtablespaces. Values can be specified in bytes or kilobytes. For example, a 16 kilobyte page size value can be specified as 16384, 16KB, or 16k.innodb_page_sizecan only be configured prior to initializing the MySQL instance and cannot be changed afterward. If no value is specified, the instance is initialized using the default page size. See Section 14.8.1, “InnoDB Startup Configuration”.The default
16KBpage size is appropriate for a wide range of workloads, particularly for queries involving table scans and DML operations involving bulk updates. Smaller page sizes might be more efficient for OLTP workloads involving many small writes, where contention can be an issue when single pages contain many rows. Smaller pages might also be efficient with SSD storage devices, which typically use small block sizes. Keeping theInnoDBpage size close to the storage device block size minimizes the amount of unchanged data that is rewritten to disk. For general I/O tuning advice, see Section 8.5.8, “Optimizing InnoDB Disk I/O”. -
Property Value Command-Line Format --innodb-print-all-deadlocks[={OFF|ON}]Introduced 5.6.2 System Variable innodb_print_all_deadlocksScope Global Dynamic Yes Type Boolean Default Value OFFWhen this option is enabled, information about all deadlocks in
InnoDBuser transactions is recorded in themysqlderror log. Otherwise, you see information about only the last deadlock, using theSHOW ENGINE INNODB STATUScommand. An occasionalInnoDBdeadlock is not necessarily an issue, becauseInnoDBdetects the condition immediately and rolls back one of the transactions automatically. You might use this option to troubleshoot why deadlocks are occurring if an application does not have appropriate error-handling logic to detect the rollback and retry its operation. A large number of deadlocks might indicate the need to restructure transactions that issue DML orSELECT ... FOR UPDATEstatements for multiple tables, so that each transaction accesses the tables in the same order, thus avoiding the deadlock condition.For related information, see Section 14.7.5, “Deadlocks in InnoDB”.
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Property Value Command-Line Format --innodb-purge-batch-size=#System Variable innodb_purge_batch_sizeScope Global Dynamic Yes Type Integer Default Value (>= 5.6.3) 300Default Value (<= 5.6.2) 20Minimum Value 1Maximum Value 5000Defines the number of undo log pages that purge parses and processes in one batch from the history list. In a multithreaded purge configuration, the coordinator purge thread divides
innodb_purge_batch_sizebyinnodb_purge_threadsand assigns that number of pages to each purge thread. Theinnodb_purge_batch_sizevariable also defines the number of undo log pages that purge frees after every 128 iterations through the undo logs.The
innodb_purge_batch_sizeoption is intended for advanced performance tuning in combination with theinnodb_purge_threadssetting. Most users need not changeinnodb_purge_batch_sizefrom its default value.For related information, see Section 14.8.10, “Purge Configuration”.
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Property Value Command-Line Format --innodb-purge-threads=#System Variable innodb_purge_threadsScope Global Dynamic No Type Integer Default Value (>= 5.6.5) 1Default Value (<= 5.6.4) 0Minimum Value (>= 5.6.5) 1Minimum Value (<= 5.6.4) 0Maximum Value (>= 5.6.2) 32Maximum Value (<= 5.6.1) 1The number of background threads devoted to the
InnoDBpurge operation. The default value is 1. Increasing the value creates additional purge threads, which can improve efficiency on systems where DML operations are performed on multiple tables. The maximum is 32.For related information, see Section 14.8.10, “Purge Configuration”.
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Property Value Command-Line Format --innodb-random-read-ahead[={OFF|ON}]Introduced 5.6.3 System Variable innodb_random_read_aheadScope Global Dynamic Yes Type Boolean Default Value OFFEnables the random read-ahead technique for optimizing
InnoDBI/O.For details about performance considerations for different types of read-ahead requests, see Section 14.8.3.3, “Configuring InnoDB Buffer Pool Prefetching (Read-Ahead)”. For general I/O tuning advice, see Section 8.5.8, “Optimizing InnoDB Disk I/O”.
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Property Value Command-Line Format --innodb-read-ahead-threshold=#System Variable innodb_read_ahead_thresholdScope Global Dynamic Yes Type Integer Default Value 56Minimum Value 0Maximum Value 64Controls the sensitivity of linear read-ahead that
InnoDBuses to prefetch pages into the buffer pool. IfInnoDBreads at leastinnodb_read_ahead_thresholdpages sequentially from an extent (64 pages), it initiates an asynchronous read for the entire following extent. The permissible range of values is 0 to 64. As of MySQL 5.6.1, a value of 0 disables read-ahead. Prior to 5.6.1, a value of 0 would trigger a read-ahead upon reading the boundary page of a 64 page extent. For the default of 56,InnoDBmust read at least 56 pages sequentially from an extent to initiate an asynchronous read for the following extent.Knowing how many pages are read through the read-ahead mechanism, and how many of these pages are evicted from the buffer pool without ever being accessed, can be useful when fine-tuning the
innodb_read_ahead_thresholdsetting.SHOW ENGINE INNODB STATUSoutput displays counter information from theInnodb_buffer_pool_read_aheadandInnodb_buffer_pool_read_ahead_evictedglobal status variables, which report the number of pages brought into the buffer pool by read-ahead requests, and the number of such pages evicted from the buffer pool without ever being accessed, respectively. The status variables report global values since the last server restart.SHOW ENGINE INNODB STATUSalso shows the rate at which the read-ahead pages are read and the rate at which such pages are evicted without being accessed. The per-second averages are based on the statistics collected since the last invocation ofSHOW ENGINE INNODB STATUSand are displayed in theBUFFER POOL AND MEMORYsection of theSHOW ENGINE INNODB STATUSoutput.For more information, see Section 14.8.3.3, “Configuring InnoDB Buffer Pool Prefetching (Read-Ahead)”. For general I/O tuning advice, see Section 8.5.8, “Optimizing InnoDB Disk I/O”.
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Property Value Command-Line Format --innodb-read-io-threads=#System Variable innodb_read_io_threadsScope Global Dynamic No Type Integer Default Value 4Minimum Value 1Maximum Value 64The number of I/O threads for read operations in
InnoDB. Its counterpart for write threads isinnodb_write_io_threads. For more information, see Section 14.8.6, “Configuring the Number of Background InnoDB I/O Threads”. For general I/O tuning advice, see Section 8.5.8, “Optimizing InnoDB Disk I/O”.NoteOn Linux systems, running multiple MySQL servers (typically more than 12) with default settings for
innodb_read_io_threads,innodb_write_io_threads, and the Linuxaio-max-nrsetting can exceed system limits. Ideally, increase theaio-max-nrsetting; as a workaround, you might reduce the settings for one or both of the MySQL variables. -
Property Value Command-Line Format --innodb-read-only[={OFF|ON}]Introduced 5.6.7 System Variable innodb_read_onlyScope Global Dynamic No Type Boolean Default Value OFFStarts
InnoDBin read-only mode. For distributing database applications or data sets on read-only media. Can also be used in data warehouses to share the same data directory between multiple instances. For more information, see Section 14.8.2, “Configuring InnoDB for Read-Only Operation”. -
Property Value Command-Line Format --innodb-replication-delay=#System Variable innodb_replication_delayScope Global Dynamic Yes Type Integer Default Value 0Minimum Value 0Maximum Value 4294967295The replication thread delay in milliseconds on a slave server if
innodb_thread_concurrencyis reached. -
Property Value Command-Line Format --innodb-rollback-on-timeout[={OFF|ON}]System Variable innodb_rollback_on_timeoutScope Global Dynamic No Type Boolean Default Value OFFInnoDBrolls back only the last statement on a transaction timeout by default. If--innodb-rollback-on-timeoutis specified, a transaction timeout causesInnoDBto abort and roll back the entire transaction (the same behavior as in MySQL 4.1).NoteIf the start-transaction statement was
START TRANSACTIONorBEGINstatement, rollback does not cancel that statement. Further SQL statements become part of the transaction until the occurrence ofCOMMIT,ROLLBACK, or some SQL statement that causes an implicit commit.For more information, see Section 14.21.4, “InnoDB Error Handling”.
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Property Value Command-Line Format --innodb-rollback-segments=#Introduced 5.6.2 System Variable innodb_rollback_segmentsScope Global Dynamic Yes Type Integer Default Value 128Minimum Value 1Maximum Value 128Defines the number of rollback segments used by
InnoDBfor transactions that generate undo records. The number of transactions that each rollback segment supports depends on theInnoDBpage size and the number of undo logs assigned to each transaction. For more information, see Section 14.6.7, “Undo Logs”.This setting is appropriate for tuning performance if you observe mutex contention related to the undo logs.
Although you can increase or decrease the number of rollback segments used by
InnoDB, the number of rollback segments physically present in the system never decreases. Thus, you might start with a low value and gradually increase it to avoid allocating rollback segments that are not required. Theinnodb_rollback_segmentsdefault and maximum value is 128.For related information, see Section 14.3, “InnoDB Multi-Versioning”. For information about configuring separate undo tablespaces, see Section 14.6.3.3, “Undo Tablespaces”.
innodb_saved_page_number_debugProperty Value Command-Line Format --innodb-saved-page-number-debug=#Introduced 5.6.17 System Variable innodb_saved_page_number_debugScope Global Dynamic Yes Type Integer Default Value 0Maximum Value 2**23-1Saves a page number. Setting the
innodb_fil_make_page_dirty_debugoption dirties the page defined byinnodb_saved_page_number_debug. Theinnodb_saved_page_number_debugoption is only available if debugging support is compiled in using theWITH_DEBUGCMake option.-
Property Value Command-Line Format --innodb-sort-buffer-size=#Introduced 5.6.4 System Variable innodb_sort_buffer_sizeScope Global Dynamic No Type Integer Default Value 1048576Minimum Value (>= 5.6.5) 65536Minimum Value (5.6.4) 524288Maximum Value 67108864Specifies the size of sort buffers used to sort data during creation of an
InnoDBindex. The specified size defines the amount of data that is read into memory for internal sorting and then written out to disk. This process is referred to as a “run”. During the merge phase, pairs of buffers of the specified size are read and merged. The larger the setting, the fewer runs and merges there are.This sort area is only used for merge sorts during index creation, not during later index maintenance operations. Buffers are deallocated when index creation completes.
The value of this option also controls the amount by which the temporary log file is extended to record concurrent DML during online DDL operations.
Before this setting was made configurable, the size was hardcoded to 1048576 bytes (1MB), which remains the default.
During an
ALTER TABLEorCREATE TABLEstatement that creates an index, 3 buffers are allocated, each with a size defined by this option. Additionally, auxiliary pointers are allocated to rows in the sort buffer so that the sort can run on pointers (as opposed to moving rows during the sort operation).For a typical sort operation, a formula such as this one can be used to estimate memory consumption:
(6 /*FTS_NUM_AUX_INDEX*/ * (3*@@GLOBAL.innodb_sort_buffer_size) + 2 * number_of_partitions * number_of_secondary_indexes_created * (@@GLOBAL.innodb_sort_buffer_size/dict_index_get_min_size(index)*/) * 8 /*64-bit sizeof *buf->tuples*/")@@GLOBAL.innodb_sort_buffer_size/dict_index_get_min_size(index)indicates the maximum tuples held.2 * (@@GLOBAL.innodb_sort_buffer_size/*dict_index_get_min_size(index)*/) * 8 /*64-bit size of *buf->tuples*/indicates auxiliary pointers allocated.NoteFor 32-bit, multiply by 4 instead of 8.
For parallel sorts on a full-text index, multiply by the
innodb_ft_sort_pll_degreesetting:(6 /*FTS_NUM_AUX_INDEX*/ * @@GLOBAL.innodb_ft_sort_pll_degree) -
Property Value Command-Line Format --innodb-spin-wait-delay=#System Variable innodb_spin_wait_delayScope Global Dynamic Yes Type Integer Default Value 6Minimum Value 0Maximum Value (64-bit platforms) 2**64-1Maximum Value (32-bit platforms) 2**32-1The maximum delay between polls for a spin lock. The low-level implementation of this mechanism varies depending on the combination of hardware and operating system, so the delay does not correspond to a fixed time interval. For more information, see Section 14.8.9, “Configuring Spin Lock Polling”.
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Property Value Command-Line Format --innodb-stats-auto-recalc[={OFF|ON}]Introduced 5.6.6 System Variable innodb_stats_auto_recalcScope Global Dynamic Yes Type Boolean Default Value ONCauses
InnoDBto automatically recalculate persistent statistics after the data in a table is changed substantially. The threshold value is 10% of the rows in the table. This setting applies to tables created when theinnodb_stats_persistentoption is enabled. Automatic statistics recalculation may also be configured by specifyingSTATS_PERSISTENT=1in aCREATE TABLEorALTER TABLEstatement. The amount of data sampled to produce the statistics is controlled by theinnodb_stats_persistent_sample_pagesvariable.For more information, see Section 14.8.11.1, “Configuring Persistent Optimizer Statistics Parameters”.
innodb_stats_include_delete_markedProperty Value Command-Line Format --innodb-stats-include-delete-marked[={OFF|ON}]Introduced 5.6.35 System Variable innodb_stats_include_delete_markedScope Global Dynamic Yes Type Boolean Default Value OFFBy default,
InnoDBreads uncommitted data when calculating statistics. In the case of an uncommitted transaction that deletes rows from a table,InnoDBexcludes records that are delete-marked when calculating row estimates and index statistics, which can lead to non-optimal execution plans for other transactions that are operating on the table concurrently using a transaction isolation level other thanREAD UNCOMMITTED. To avoid this scenario,innodb_stats_include_delete_markedcan be enabled to ensure thatInnoDBincludes delete-marked records when calculating persistent optimizer statistics.When
innodb_stats_include_delete_markedis enabled,ANALYZE TABLEconsiders delete-marked records when recalculating statistics.innodb_stats_include_delete_markedis a global setting that affects allInnoDBtables. It is only applicable to persistent optimizer statistics.For related information, see Section 14.8.11.1, “Configuring Persistent Optimizer Statistics Parameters”.
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Property Value Command-Line Format --innodb-stats-method=valueIntroduced 5.6.2 System Variable innodb_stats_methodScope Global Dynamic Yes Type Enumeration Default Value nulls_equalValid Values nulls_equalnulls_unequalnulls_ignoredHow the server treats
NULLvalues when collecting statistics about the distribution of index values forInnoDBtables. Permitted values arenulls_equal,nulls_unequal, andnulls_ignored. Fornulls_equal, allNULLindex values are considered equal and form a single value group with a size equal to the number ofNULLvalues. Fornulls_unequal,NULLvalues are considered unequal, and eachNULLforms a distinct value group of size 1. Fornulls_ignored,NULLvalues are ignored.The method used to generate table statistics influences how the optimizer chooses indexes for query execution, as described in Section 8.3.7, “InnoDB and MyISAM Index Statistics Collection”.
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Property Value Command-Line Format --innodb-stats-on-metadata[={OFF|ON}]System Variable innodb_stats_on_metadataScope Global Dynamic Yes Type Boolean Default Value (>= 5.6.6) OFFDefault Value (<= 5.6.5) ONThis option only applies when optimizer statistics are configured to be non-persistent. Optimizer statistics are not persisted to disk when
innodb_stats_persistentis disabled or when individual tables are created or altered withSTATS_PERSISTENT=0. For more information, see Section 14.8.11.2, “Configuring Non-Persistent Optimizer Statistics Parameters”.When
innodb_stats_on_metadatais enabled,InnoDBupdates non-persistent statistics when metadata statements such asSHOW TABLE STATUSorSHOW INDEXare run, or when accessing theINFORMATION_SCHEMA.TABLESorINFORMATION_SCHEMA.STATISTICStables. (These updates are similar to what happens forANALYZE TABLE.) When disabled,InnoDBdoes not update statistics during these operations. Leaving the setting disabled can improve access speed for schemas that have a large number of tables or indexes. It can also improve the stability of execution plans for queries that involveInnoDBtables.To change the setting, issue the statement
SET GLOBAL innodb_stats_on_metadata=, wheremodemodeONorOFF(or1or0). Changing the setting requires privileges sufficient to set global system variables (see Section 5.1.8.1, “System Variable Privileges”) and immediately affects the operation of all connections. -
Property Value Command-Line Format --innodb-stats-persistent[={OFF|ON}]Introduced 5.6.6 System Variable innodb_stats_persistentScope Global Dynamic Yes Type Boolean Default Value ONSpecifies whether
InnoDBindex statistics are persisted to disk. Otherwise, statistics may be recalculated frequently which can lead to variations in query execution plans. This setting is stored with each table when the table is created. You can setinnodb_stats_persistentat the global level before creating a table, or use theSTATS_PERSISTENTclause of theCREATE TABLEandALTER TABLEstatements to override the system-wide setting and configure persistent statistics for individual tables.For more information, see Section 14.8.11.1, “Configuring Persistent Optimizer Statistics Parameters”.
innodb_stats_persistent_sample_pagesProperty Value Command-Line Format --innodb-stats-persistent-sample-pages=#Introduced 5.6.2 System Variable innodb_stats_persistent_sample_pagesScope Global Dynamic Yes Type Integer Default Value 20The number of index pages to sample when estimating cardinality and other statistics for an indexed column, such as those calculated by
ANALYZE TABLE. Increasing the value improves the accuracy of index statistics, which can improve the query execution plan, at the expense of increased I/O during the execution ofANALYZE TABLEfor anInnoDBtable. For more information, see Section 14.8.11.1, “Configuring Persistent Optimizer Statistics Parameters”.NoteSetting a high value for
innodb_stats_persistent_sample_pagescould result in lengthyANALYZE TABLEexecution time. To estimate the number of database pages accessed byANALYZE TABLE, see Section 14.8.11.3, “Estimating ANALYZE TABLE Complexity for InnoDB Tables”.innodb_stats_persistent_sample_pagesonly applies wheninnodb_stats_persistentis enabled for a table; wheninnodb_stats_persistentis disabled,innodb_stats_transient_sample_pagesapplies instead.-
Property Value Command-Line Format --innodb-stats-sample-pages=#Deprecated 5.6.3 System Variable innodb_stats_sample_pagesScope Global Dynamic Yes Type Integer Default Value 8Minimum Value 1Maximum Value 2**64-1Deprecated. Use
innodb_stats_transient_sample_pagesinstead. innodb_stats_transient_sample_pagesProperty Value Command-Line Format --innodb-stats-transient-sample-pages=#Introduced 5.6.2 System Variable innodb_stats_transient_sample_pagesScope Global Dynamic Yes Type Integer Default Value 8The number of index pages to sample when estimating cardinality and other statistics for an indexed column, such as those calculated by
ANALYZE TABLE. The default value is 8. Increasing the value improves the accuracy of index statistics, which can improve the query execution plan, at the expense of increased I/O when opening anInnoDBtable or recalculating statistics. For more information, see Section 14.8.11.2, “Configuring Non-Persistent Optimizer Statistics Parameters”.NoteSetting a high value for
innodb_stats_transient_sample_pagescould result in lengthyANALYZE TABLEexecution time. To estimate the number of database pages accessed byANALYZE TABLE, see Section 14.8.11.3, “Estimating ANALYZE TABLE Complexity for InnoDB Tables”.innodb_stats_transient_sample_pagesonly applies wheninnodb_stats_persistentis disabled for a table; wheninnodb_stats_persistentis enabled,innodb_stats_persistent_sample_pagesapplies instead. Takes the place ofinnodb_stats_sample_pages. For more information, see Section 14.8.11.2, “Configuring Non-Persistent Optimizer Statistics Parameters”.-
Property Value Command-Line Format --innodb-status-output[={OFF|ON}]Introduced 5.6.16 System Variable innodb_status_outputScope Global Dynamic Yes Type Boolean Default Value OFFEnables or disables periodic output for the standard
InnoDBMonitor. Also used in combination withinnodb_status_output_locksto enable or disable periodic output for theInnoDBLock Monitor. For more information, see Section 14.17.2, “Enabling InnoDB Monitors”. -
Property Value Command-Line Format --innodb-status-output-locks[={OFF|ON}]Introduced 5.6.16 System Variable innodb_status_output_locksScope Global Dynamic Yes Type Boolean Default Value OFFEnables or disables the
InnoDBLock Monitor. When enabled, theInnoDBLock Monitor prints additional information about locks inSHOW ENGINE INNODB STATUSoutput and in periodic output printed to the MySQL error log. Periodic output for theInnoDBLock Monitor is printed as part of the standardInnoDBMonitor output. The standardInnoDBMonitor must therefore be enabled for theInnoDBLock Monitor to print data to the MySQL error log periodically. For more information, see Section 14.17.2, “Enabling InnoDB Monitors”. -
Property Value Command-Line Format --innodb-strict-mode[={OFF|ON}]System Variable innodb_strict_modeScope Global, Session Dynamic Yes Type Boolean Default Value OFFWhen
innodb_strict_modeis enabled,InnoDBreturns errors rather than warnings for certain conditions.Strict mode helps guard against ignored typos and syntax errors in SQL, or other unintended consequences of various combinations of operational modes and SQL statements. When
innodb_strict_modeis enabled,InnoDBraises error conditions in certain cases, rather than issuing a warning and processing the specified statement (perhaps with unintended behavior). This is analogous tosql_modein MySQL, which controls what SQL syntax MySQL accepts, and determines whether it silently ignores errors, or validates input syntax and data values.The
innodb_strict_modesetting affects the handling of syntax errors forCREATE TABLE,ALTER TABLEandCREATE INDEXstatements.innodb_strict_modealso enables a record size check, so that anINSERTorUPDATEnever fails due to the record being too large for the selected page size.Oracle recommends enabling
innodb_strict_modewhen usingROW_FORMATandKEY_BLOCK_SIZEclauses inCREATE TABLE,ALTER TABLE, andCREATE INDEXstatements. Wheninnodb_strict_modeis disabled,InnoDBignores conflicting clauses and creates the table or index with only a warning in the message log. The resulting table might have different characteristics than intended, such as lack of compression support when attempting to create a compressed table. Wheninnodb_strict_modeis enabled, such problems generate an immediate error and the table or index is not created.You can enable or disable
innodb_strict_modeon the command line when startingmysqld, or in a MySQL configuration file. You can also enable or disableinnodb_strict_modeat runtime with the statementSET [GLOBAL|SESSION] innodb_strict_mode=, wheremodemodeONorOFF. Changing theGLOBALsetting requires privileges sufficient to set global system variables (see Section 5.1.8.1, “System Variable Privileges”) and affects the operation of all clients that subsequently connect. Any client can change theSESSIONsetting forinnodb_strict_mode, and the setting affects only that client. -
Property Value Command-Line Format --innodb-support-xa[={OFF|ON}]System Variable innodb_support_xaScope Global, Session Dynamic Yes Type Boolean Default Value ONEnables
InnoDBsupport for two-phase commit in XA transactions, causing an extra disk flush for transaction preparation. The XA mechanism is used internally and is essential for any server that has its binary log turned on and is accepting changes to its data from more than one thread. If you disableinnodb_support_xa, transactions can be written to the binary log in a different order than the live database is committing them, which can produce different data when the binary log is replayed in disaster recovery or on a replication slave. Do not disableinnodb_support_xaon a replication master server unless you have an unusual setup where only one thread is able to change data.For a server that is accepting data changes from only one thread, it is safe and recommended to disable this option to improve performance for
InnoDBtables. For example, you can turn it off on replication slaves where only the replication SQL thread is changing data.You can also disable this option if you do not need it for safe binary logging or replication, and you also do not use an external XA transaction manager.
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Property Value Command-Line Format --innodb-sync-array-size=#Introduced 5.6.3 System Variable innodb_sync_array_sizeScope Global Dynamic No Type Integer Default Value 1Minimum Value 1Maximum Value 1024Defines the size of the mutex/lock wait array. Increasing the value splits the internal data structure used to coordinate threads, for higher concurrency in workloads with large numbers of waiting threads. This setting must be configured when the MySQL instance is starting up, and cannot be changed afterward. Increasing the value is recommended for workloads that frequently produce a large number of waiting threads, typically greater than 768.
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Property Value Command-Line Format --innodb-sync-spin-loops=#System Variable innodb_sync_spin_loopsScope Global Dynamic Yes Type Integer Default Value 30Minimum Value 0Maximum Value 4294967295The number of times a thread waits for an
InnoDBmutex to be freed before the thread is suspended. -
Property Value Command-Line Format --innodb-table-locks[={OFF|ON}]System Variable innodb_table_locksScope Global, Session Dynamic Yes Type Boolean Default Value ONIf
autocommit = 0,InnoDBhonorsLOCK TABLES; MySQL does not return fromLOCK TABLES ... WRITEuntil all other threads have released all their locks to the table. The default value ofinnodb_table_locksis 1, which means thatLOCK TABLEScauses InnoDB to lock a table internally ifautocommit = 0.In MySQL 5.6,
innodb_table_locks = 0has no effect for tables locked explicitly withLOCK TABLES ... WRITE. It does have an effect for tables locked for read or write byLOCK TABLES ... WRITEimplicitly (for example, through triggers) or byLOCK TABLES ... READ.For related information, see Section 14.7, “InnoDB Locking and Transaction Model”.
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Property Value Command-Line Format --innodb-thread-concurrency=#System Variable innodb_thread_concurrencyScope Global Dynamic Yes Type Integer Default Value 0Minimum Value 0Maximum Value 1000InnoDBtries to keep the number of operating system threads concurrently insideInnoDBless than or equal to the limit given by this variable (InnoDBuses operating system threads to process user transactions). Once the number of threads reaches this limit, additional threads are placed into a wait state within a “First In, First Out” (FIFO) queue for execution. Threads waiting for locks are not counted in the number of concurrently executing threads.The range of this variable is 0 to 1000. A value of 0 (the default) is interpreted as infinite concurrency (no concurrency checking). Disabling thread concurrency checking enables
InnoDBto create as many threads as it needs. A value of 0 also disables thequeries inside InnoDBandqueries in queue countersin theROW OPERATIONSsection ofSHOW ENGINE INNODB STATUSoutput.Consider setting this variable if your MySQL instance shares CPU resources with other applications, or if your workload or number of concurrent users is growing. The correct setting depends on workload, computing environment, and the version of MySQL that you are running. You will need to test a range of values to determine the setting that provides the best performance.
innodb_thread_concurrencyis a dynamic variable, which allows you to experiment with different settings on a live test system. If a particular setting performs poorly, you can quickly setinnodb_thread_concurrencyback to 0.Use the following guidelines to help find and maintain an appropriate setting:
If the number of concurrent user threads for a workload is less than 64, set
innodb_thread_concurrency=0.If your workload is consistently heavy or occasionally spikes, start by setting
innodb_thread_concurrency=128and then lowering the value to 96, 80, 64, and so on, until you find the number of threads that provides the best performance. Suppose that your system typically has 40 to 50 users, but periodically the number increases to 60, 70, or even 200. You find that performance is stable at 80 concurrent users but starts to show a regression above this number. In this case, you would setinnodb_thread_concurrency=80to avoid impacting performance.If you do not want
InnoDBto use more than a certain number of virtual CPUs for user threads (20 virtual CPUs, for example), setinnodb_thread_concurrencyto this number (or possibly lower, depending on performance results). If your goal is to isolate MySQL from other applications, you may consider binding themysqldprocess exclusively to the virtual CPUs. Be aware, however, that exclusive binding could result in non-optimal hardware usage if themysqldprocess is not consistently busy. In this case, you might bind themysqldprocess to the virtual CPUs but also allow other applications to use some or all of the virtual CPUs.NoteFrom an operating system perspective, using a resource management solution to manage how CPU time is shared among applications may be preferable to binding the
mysqldprocess. For example, you could assign 90% of virtual CPU time to a given application while other critical processes are not running, and scale that value back to 40% when other critical processes are running.innodb_thread_concurrencyvalues that are too high can cause performance regression due to increased contention on system internals and resources.In some cases, the optimal
innodb_thread_concurrencysetting can be smaller than the number of virtual CPUs.Monitor and analyze your system regularly. Changes to workload, number of users, or computing environment may require that you adjust the
innodb_thread_concurrencysetting.
For related information, see Section 14.8.5, “Configuring Thread Concurrency for InnoDB”.
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Property Value Command-Line Format --innodb-thread-sleep-delay=#System Variable innodb_thread_sleep_delayScope Global Dynamic Yes Type Integer Default Value 10000Minimum Value 0Maximum Value (64-bit platforms, <= 5.6.16) 18446744073709551615Maximum Value (32-bit platforms, <= 5.6.16) 4294967295Maximum Value (>= 5.6.17) 1000000Defines how long
InnoDBthreads sleep before joining theInnoDBqueue, in microseconds. The default value is 10000. A value of 0 disables sleep. You can setinnodb_adaptive_max_sleep_delayto the highest value you would allow forinnodb_thread_sleep_delay, andInnoDBautomatically adjustsinnodb_thread_sleep_delayup or down depending on current thread-scheduling activity. This dynamic adjustment helps the thread scheduling mechanism to work smoothly during times when the system is lightly loaded or when it is operating near full capacity.For more information, see Section 14.8.5, “Configuring Thread Concurrency for InnoDB”.
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Property Value Command-Line Format --innodb-tmpdir=dir_nameIntroduced 5.6.29 System Variable innodb_tmpdirScope Global, Session Dynamic Yes Type Directory name Default Value NULLUsed to define an alternate directory for temporary sort files created during online
ALTER TABLEoperations that rebuild the table.Online
ALTER TABLEoperations that rebuild the table also create an intermediate table file in the same directory as the original table. Theinnodb_tmpdiroption is not applicable to intermediate table files.A valid value is any directory path other than the MySQL data directory path. If the value is NULL (the default), temporary files are created MySQL temporary directory (
$TMPDIRon Unix,%TEMP%on Windows, or the directory specified by the--tmpdirconfiguration option). If a directory is specified, existence of the directory and permissions are only checked wheninnodb_tmpdiris configured using aSETstatement. If a symlink is provided in a directory string, the symlink is resolved and stored as an absolute path. The path should not exceed 512 bytes. An onlineALTER TABLEoperation reports an error ifinnodb_tmpdiris set to an invalid directory.innodb_tmpdiroverrides the MySQLtmpdirsetting but only for onlineALTER TABLEoperations.The
FILEprivilege is required to configureinnodb_tmpdir.The
innodb_tmpdiroption was introduced to help avoid overflowing a temporary file directory located on atmpfsfile system. Such overflows could occur as a result of large temporary sort files created during onlineALTER TABLEoperations that rebuild the table.In replication environments, only consider replicating the
innodb_tmpdirsetting if all servers have the same operating system environment. Otherwise, replicating theinnodb_tmpdirsetting could result in a replication failure when running onlineALTER TABLEoperations that rebuild the table. If server operating environments differ, it is recommended that you configureinnodb_tmpdiron each server individually.For more information, see Section 14.13.3, “Online DDL Space Requirements”. For information about online
ALTER TABLEoperations, see Section 14.13, “InnoDB and Online DDL”. innodb_trx_purge_view_update_only_debugProperty Value Command-Line Format --innodb-trx-purge-view-update-only-debug[={OFF|ON}]System Variable innodb_trx_purge_view_update_only_debugScope Global Dynamic Yes Type Boolean Default Value OFFPauses purging of delete-marked records while allowing the purge view to be updated. This option artificially creates a situation in which the purge view is updated but purges have not yet been performed. This option is only available if debugging support is compiled in using the
WITH_DEBUGCMake option.-
Property Value Command-Line Format --innodb-trx-rseg-n-slots-debug=#System Variable innodb_trx_rseg_n_slots_debugScope Global Dynamic Yes Type Integer Default Value 0Maximum Value 1024Sets a debug flag that limits
TRX_RSEG_N_SLOTSto a given value for thetrx_rsegf_undo_find_freefunction that looks for free slots for undo log segments. This option is only available if debugging support is compiled in using theWITH_DEBUGCMake option. -
Property Value Command-Line Format --innodb-undo-directory=dir_nameIntroduced 5.6.3 System Variable innodb_undo_directoryScope Global Dynamic No Type Directory name Default Value .The relative or absolute directory path where
InnoDBcreates undo tablespaces. Typically used to place undo logs on a different storage device. Used in conjunction withinnodb_rollback_segmentsandinnodb_undo_tablespaces. The default value of “.” represents the same directory whereInnoDBcreates its other log files by default.NoteAn absolute directory path must be set for embedded MySQL installations. Otherwise, the server may not be able to locate undo tablespaces that are created when the MySQL instance is initialized.
For more information, see Section 14.6.3.3, “Undo Tablespaces”.
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Property Value Command-Line Format --innodb-undo-logs=#Introduced 5.6.3 System Variable innodb_undo_logsScope Global Dynamic Yes Type Integer Default Value 128Minimum Value 1Maximum Value 128Defines the number of rollback segments used by
InnoDB. Theinnodb_undo_logsoption is an alias forinnodb_rollback_segments. For more information, see the description ofinnodb_rollback_segments. -
Property Value Command-Line Format --innodb-undo-tablespaces=#Introduced 5.6.3 System Variable innodb_undo_tablespacesScope Global Dynamic No Type Integer Default Value 0Minimum Value 0Maximum Value 126The number of undo tablespaces used by
InnoDB. The default value is 0.Because undo logs can become large during long-running transactions, having undo logs in multiple tablespaces reduces the maximum size of any one tablespace. The undo tablespace files are created in the location defined by
innodb_undo_directory, with names in the form ofundo, whereNNis a sequential series of integers (including leading zeros) representing the space ID. The default size of an undo tablespace file is 10MiB.Importantinnodb_undo_tablespacescan only be configured prior to initializing the MySQL instance and cannot be changed afterward. If no value is specified, the instance is initialized using the default setting of 0. Attempting to restartInnoDBwith a greater number of undo tablespaces than specified when the MySQL instance was initialized results in a startup failure and an error stating thatInnoDBdid not find the expected number of undo tablespaces.For more information, see Section 14.6.3.3, “Undo Tablespaces”.
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Property Value Command-Line Format --innodb-use-native-aio[={OFF|ON}]System Variable innodb_use_native_aioScope Global Dynamic No Type Boolean Default Value ONSpecifies whether to use the Linux asynchronous I/O subsystem. This variable applies to Linux systems only, and cannot be changed while the server is running. Normally, you do not need to configure this option, because it is enabled by default.
The asynchronous I/O capability that
InnoDBhas on Windows systems is available on Linux systems. (Other Unix-like systems continue to use synchronous I/O calls.) This feature improves the scalability of heavily I/O-bound systems, which typically show many pending reads/writes inSHOW ENGINE INNODB STATUS\Goutput.Running with a large number of
InnoDBI/O threads, and especially running multiple such instances on the same server machine, can exceed capacity limits on Linux systems. In this case, you may receive the following error:EAGAIN: The specified maxevents exceeds the user's limit of available events.You can typically address this error by writing a higher limit to
/proc/sys/fs/aio-max-nr.However, if a problem with the asynchronous I/O subsystem in the OS prevents
InnoDBfrom starting, you can start the server withinnodb_use_native_aio=0. This option may also be disabled automatically during startup ifInnoDBdetects a potential problem such as a combination oftmpdirlocation,tmpfsfile system, and Linux kernel that does not support AIO ontmpfs.For more information, see Section 14.8.7, “Using Asynchronous I/O on Linux”.
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Property Value Command-Line Format --innodb-use-sys-malloc[={OFF|ON}]Deprecated 5.6.3 System Variable innodb_use_sys_mallocScope Global Dynamic No Type Boolean Default Value ONEnables the operating system memory allocator. If disabled,
InnoDBuses its own allocator. The default value isON. For more information, see Section 14.8.4, “Configuring the Memory Allocator for InnoDB”.innodb_use_sys_mallocis deprecated and will be removed in a future MySQL release. The
InnoDBversion number. Starting in MySQL 5.6.11, separate version numbering forInnoDBis discontinued and this value is the same theversionnumber of the server.-
Property Value Command-Line Format --innodb-write-io-threads=#System Variable innodb_write_io_threadsScope Global Dynamic No Type Integer Default Value 4Minimum Value 1Maximum Value 64The number of I/O threads for write operations in
InnoDB. The default value is 4. Its counterpart for read threads isinnodb_read_io_threads. For more information, see Section 14.8.6, “Configuring the Number of Background InnoDB I/O Threads”. For general I/O tuning advice, see Section 8.5.8, “Optimizing InnoDB Disk I/O”.NoteOn Linux systems, running multiple MySQL servers (typically more than 12) with default settings for
innodb_read_io_threads,innodb_write_io_threads, and the Linuxaio-max-nrsetting can exceed system limits. Ideally, increase theaio-max-nrsetting; as a workaround, you might reduce the settings for one or both of the MySQL variables.
Also take into consideration the value of
sync_binlog, which controls
synchronization of the binary log to disk.
For general I/O tuning advice, see Section 8.5.8, “Optimizing InnoDB Disk I/O”.