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• InnoDB Startup Options

• InnoDB System Variables

• 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 theInnoDB adaptive hash index, you can use--innodb-adaptive-hash-index or--skip-innodb-adaptive-hash-index on the command line, orinnodb_adaptive_hash_index orskip_innodb_adaptive_hash_index in an option file.

• Some variable descriptions refer to“enabling” or“disabling” a variable. These variables can be enabled with theSET statement by setting them toON or1, or disabled by setting them toOFF or0. Boolean variables can be set at startup to the valuesON,TRUE,OFF, andFALSE (not case-sensitive), as well as1 and0. SeeSection 6.2.2.4, “Program Option Modifiers”.

• System variables that take a numeric value can be specified as--var_name=value on the command line or asvar_name=value in option files.

• Many system variables can be changed at runtime (seeSection 7.1.9.2, “Dynamic System Variables”).

• For information aboutGLOBAL andSESSION variable scope modifiers, refer to theSET statement documentation.

• Certain options control the locations and layout of theInnoDB data files.Section 17.8.1, “InnoDB Startup Configuration” explains how to use these options.

• Some options, which you might not use initially, help tuneInnoDB performance characteristics based on machine capacity and your databaseworkload.

• For more information on specifying options and system variables, seeSection 6.2.2, “Specifying Program Options”.

Table 17.24 InnoDB Option and Variable Reference

• --innodb[=value]

  Command-Line Format	--innodb[=value]
  Deprecated	Yes
  Type	Enumeration
  Default Value	ON
  Valid Values	OFF ON FORCE

  Controls loading of theInnoDB storage engine, if the server was compiled withInnoDB support. This option has a tristate format, with possible values ofOFF,ON, orFORCE. SeeSection 7.6.1, “Installing and Uninstalling Plugins”.

  To disableInnoDB, use--innodb=OFF or--skip-innodb. In this case, because the default storage engine isInnoDB, the server does not start unless you also use--default-storage-engine and--default-tmp-storage-engine to set the default to some other engine for both permanent andTEMPORARY tables.

  TheInnoDB storage engine can no longer be disabled, and the--innodb=OFF and--skip-innodb options are deprecated and have no effect. Their use results in a warning. Expect these options to be removed in a future MySQL release.

• --innodb-dedicated-server

  Command-Line Format	--innodb-dedicated-server[={OFF|ON}]
  System Variable	innodb_dedicated_server
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  When this option is set by starting the server with--innodb-dedicated-server or--innodb-dedicated-server=ON, either on the command line or in amy.cnf file,InnoDB automatically calculates and sets the values of the following variables:

  • innodb_buffer_pool_size

  • innodb_redo_log_capacity or, prior to MySQL 8.0.30,innodb_log_file_size andinnodb_log_files_in_group.

  • innodb_flush_method

  Note

  innodb_log_file_size andinnodb_log_files_in_group are deprecated in MySQL 8.0.30. These variables are superseded byinnodb_redo_log_capacity. SeeSection 17.6.5, “Redo Log”.

  You should consider using--innodb-dedicated-server only if the MySQL instance resides on a dedicated server where it can use all available system resources. Using this option is not recommended if the MySQL instance shares system resources with other applications.

  It is strongly recommended that you readSection 17.8.12, “Enabling Automatic InnoDB Configuration for a Dedicated MySQL Server”, before using this option in production.

• --innodb-status-file

  Command-Line Format	--innodb-status-file[={OFF|ON}]
  Type	Boolean
  Default Value	OFF

  The--innodb-status-file startup option controls whetherInnoDB creates a file namedinnodb_status.pid in the data directory and writesSHOW ENGINE INNODB STATUS output to it every 15 seconds, approximately.

  Theinnodb_status.pid file is not created by default. To create it, startmysqld with the--innodb-status-file option.InnoDB removes 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-file option is intended for temporary use, asSHOW ENGINE INNODB STATUS output generation can affect performance, and theinnodb_status.pid file can become quite large over time.

  For related information, seeSection 17.17.2, “Enabling InnoDB Monitors”.

• --skip-innodb

  Disable theInnoDB storage engine. See the description of--innodb.

• daemon_memcached_enable_binlog

  Command-Line Format	--daemon-memcached-enable-binlog[={OFF|ON}]
  Deprecated	8.0.22
  System Variable	daemon_memcached_enable_binlog
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  Enable this option on the source server to use theInnoDBmemcached plugin (daemon_memcached) with the MySQLbinary log. This option can only be set at server startup. You must also enable the MySQL binary log on the source server using the--log-bin option.

  For more information, seeSection 17.20.7, “The InnoDB memcached Plugin and Replication”.

• daemon_memcached_engine_lib_name

  Command-Line Format	--daemon-memcached-engine-lib-name=file_name
  Deprecated	8.0.22
  System Variable	daemon_memcached_engine_lib_name
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	File name
  Default Value	innodb_engine.so

  Specifies the shared library that implements theInnoDBmemcached plugin.

  For more information, seeSection 17.20.3, “Setting Up the InnoDB memcached Plugin”.

• daemon_memcached_engine_lib_path

  Command-Line Format	--daemon-memcached-engine-lib-path=dir_name
  Deprecated	8.0.22
  System Variable	daemon_memcached_engine_lib_path
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Directory name
  Default Value	NULL

  The path of the directory containing the shared library that implements theInnoDBmemcached plugin. The default value is NULL, representing the MySQL plugin directory. You should not need to modify this parameter unless specifying amemcached plugin for a different storage engine that is located outside of the MySQL plugin directory.

  For more information, seeSection 17.20.3, “Setting Up the InnoDB memcached Plugin”.

• daemon_memcached_option

  Command-Line Format	--daemon-memcached-option=options
  Deprecated	8.0.22
  System Variable	daemon_memcached_option
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	String
  Default Value

  Used to pass space-separated memcached options to the underlyingmemcached memory object caching daemon on startup. For example, you might change the port thatmemcached 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.

  SeeSection 17.20.3, “Setting Up the InnoDB memcached Plugin” for usage details. For information aboutmemcached options, refer to thememcached man page.

• daemon_memcached_r_batch_size

  Command-Line Format	--daemon-memcached-r-batch-size=#
  Deprecated	8.0.22
  System Variable	daemon_memcached_r_batch_size
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	1
  Minimum Value	1
  Maximum Value	1073741824

  Specifies how manymemcached read operations (get operations) to perform before doing aCOMMIT to 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 tomemcached operations. You might increase it to reduce the overhead from frequent commits on a system where the underlying table is only being accessed through thememcached 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, seeSection 17.20.3, “Setting Up the InnoDB memcached Plugin”.

• daemon_memcached_w_batch_size

  Command-Line Format	--daemon-memcached-w-batch-size=#
  Deprecated	8.0.22
  System Variable	daemon_memcached_w_batch_size
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	1
  Minimum Value	1
  Maximum Value	1048576

  Specifies how manymemcached write operations, such asadd,set, andincr, to perform before doing aCOMMIT to 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 lastN-1 uncommitted write operations could be lost if an unexpected exit occurs.

  For more information, seeSection 17.20.3, “Setting Up the InnoDB memcached Plugin”.

• innodb_adaptive_flushing

  Command-Line Format	--innodb-adaptive-flushing[={OFF|ON}]
  System Variable	innodb_adaptive_flushing
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON

  Specifies whether to dynamically adjust the rate of flushingdirty pages in theInnoDBbuffer 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. SeeSection 17.8.3.5, “Configuring Buffer Pool Flushing” for more information. For general I/O tuning advice, seeSection 10.5.8, “Optimizing InnoDB Disk I/O”.

• innodb_adaptive_flushing_lwm

  Command-Line Format	--innodb-adaptive-flushing-lwm=#
  System Variable	innodb_adaptive_flushing_lwm
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	10
  Minimum Value	0
  Maximum Value	70

  Defines the low water mark representing percentage ofredo log capacity at whichadaptive flushing is enabled. For more information, seeSection 17.8.3.5, “Configuring Buffer Pool Flushing”.

• innodb_adaptive_hash_index

  Command-Line Format	--innodb-adaptive-hash-index[={OFF|ON}]
  System Variable	innodb_adaptive_hash_index
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON

  Whether theInnoDBadaptive hash index is enabled or disabled. It may be desirable, depending on your workload, to dynamically enable or disableadaptive 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. SeeSection 17.5.3, “Adaptive Hash Index” for details.

  This variable is enabled by default. You can modify this parameter using theSET GLOBAL statement, without restarting the server. Changing the setting at runtime requires privileges sufficient to set global system variables. SeeSection 7.1.9.1, “System Variable Privileges”. You can also use--skip-innodb-adaptive-hash-index at 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_hash_index_parts

  Command-Line Format	--innodb-adaptive-hash-index-parts=#
  System Variable	innodb_adaptive_hash_index_parts
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Numeric
  Default Value	8
  Minimum Value	1
  Maximum Value	512

  Partitions the adaptive hash index search system. Each index is bound to a specific partition, with each partition protected by a separate latch.

  The adaptive hash index search system is partitioned into 8 parts by default. The maximum setting is 512.

  For related information, seeSection 17.5.3, “Adaptive Hash Index”.

• innodb_adaptive_max_sleep_delay

  Command-Line Format	--innodb-adaptive-max-sleep-delay=#
  System Variable	innodb_adaptive_max_sleep_delay
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	150000
  Minimum Value	0
  Maximum Value	1000000
  Unit	microseconds

  PermitsInnoDB to automatically adjust the value ofinnodb_thread_sleep_delay up or down according to the current workload. Any nonzero value enables automated, dynamic adjustment of theinnodb_thread_sleep_delay value, up to the maximum value specified in theinnodb_adaptive_max_sleep_delay option. The value represents the number of microseconds. This option can be useful in busy systems, with greater than 16InnoDB threads. (In practice, it is most valuable for MySQL systems with hundreds or thousands of simultaneous connections.)

  For more information, seeSection 17.8.4, “Configuring Thread Concurrency for InnoDB”.

• innodb_api_bk_commit_interval

  Command-Line Format	--innodb-api-bk-commit-interval=#
  Deprecated	8.0.22
  System Variable	innodb_api_bk_commit_interval
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	5
  Minimum Value	1
  Maximum Value	1073741824
  Unit	seconds

  How often to auto-commit idle connections that use theInnoDBmemcached interface, in seconds. For more information, seeSection 17.20.6.4, “Controlling Transactional Behavior of the InnoDB memcached Plugin”.

• innodb_api_disable_rowlock

  Command-Line Format	--innodb-api-disable-rowlock[={OFF|ON}]
  Deprecated	8.0.22
  System Variable	innodb_api_disable_rowlock
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  Use this option to disable row locks whenInnoDBmemcached performs DML operations. By default,innodb_api_disable_rowlock is disabled, which means thatmemcached requests row locks forget andset operations. Wheninnodb_api_disable_rowlock is enabled,memcached requests a table lock instead of row locks.

  innodb_api_disable_rowlock is not dynamic. It must be specified on themysqld 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, seeSection 17.20.6.4, “Controlling Transactional Behavior of the InnoDB memcached Plugin”.

• innodb_api_enable_binlog

  Command-Line Format	--innodb-api-enable-binlog[={OFF|ON}]
  Deprecated	8.0.22
  System Variable	innodb_api_enable_binlog
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  Lets you use theInnoDBmemcached plugin with the MySQLbinary log. For more information, seeEnabling the InnoDB memcached Binary Log.

• innodb_api_enable_mdl

  Command-Line Format	--innodb-api-enable-mdl[={OFF|ON}]
  Deprecated	8.0.22
  System Variable	innodb_api_enable_mdl
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  Locks the table used by theInnoDBmemcached plugin, so that it cannot be dropped or altered byDDL through the SQL interface. For more information, seeSection 17.20.6.4, “Controlling Transactional Behavior of the InnoDB memcached Plugin”.

• innodb_api_trx_level

  Command-Line Format	--innodb-api-trx-level=#
  Deprecated	8.0.22
  System Variable	innodb_api_trx_level
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	0
  Minimum Value	0
  Maximum Value	3

  Controls the transactionisolation level on queries processed by thememcached interface. The constants corresponding to the familiar names are:

  • 0 =READ UNCOMMITTED

  • 1 =READ COMMITTED

  • 2 =REPEATABLE READ

  • 3 =SERIALIZABLE

  For more information, seeSection 17.20.6.4, “Controlling Transactional Behavior of the InnoDB memcached Plugin”.

• innodb_autoextend_increment

  Command-Line Format	--innodb-autoextend-increment=#
  System Variable	innodb_autoextend_increment
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	64
  Minimum Value	1
  Maximum Value	1000
  Unit	megabytes

  The increment size (in megabytes) for extending the size of an auto-extendingInnoDBsystem tablespace file when it becomes full. The default value is 64. For related information, seeSystem Tablespace Data File Configuration, andResizing the System Tablespace.

  Theinnodb_autoextend_increment setting does not affectfile-per-table tablespace files orgeneral tablespace files. These files are auto-extending regardless of theinnodb_autoextend_increment setting. The initial extensions are by small amounts, after which extensions occur in increments of 4MB.

• innodb_autoinc_lock_mode

  Command-Line Format	--innodb-autoinc-lock-mode=#
  System Variable	innodb_autoinc_lock_mode
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	2
  Valid Values	0 1 2

  Thelock mode to use for generatingauto-increment values. Permissible values are 0, 1, or 2, for traditional, consecutive, or interleaved, respectively.

  The default setting is 2 (interleaved) as of MySQL 8.0, and 1 (consecutive) before that. The change to interleaved lock mode as the default setting reflects the change from statement-based to row-based replication as the default replication type, which occurred in MySQL 5.7. Statement-based replication requires the consecutive auto-increment lock mode to ensure that auto-increment values are assigned in a predictable and repeatable order for a given sequence of SQL statements, whereas row-based replication is not sensitive to the execution order of SQL statements.

  For the characteristics of each lock mode, seeInnoDB AUTO_INCREMENT Lock Modes.

• innodb_background_drop_list_empty

  Command-Line Format	--innodb-background-drop-list-empty[={OFF|ON}]
  System Variable	innodb_background_drop_list_empty
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  Enabling theinnodb_background_drop_list_empty debug option helps avoid test case failures by delaying table creation until the background drop list is empty. For example, if test case A places tablet1 on the background drop list, test case B waits until the background drop list is empty before creating tablet1.

• innodb_buffer_pool_chunk_size

  Command-Line Format	--innodb-buffer-pool-chunk-size=#
  System Variable	innodb_buffer_pool_chunk_size
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	134217728
  Minimum Value	1048576
  Maximum Value	innodb_buffer_pool_size / innodb_buffer_pool_instances
  Unit	bytes

  innodb_buffer_pool_chunk_size defines the chunk size forInnoDB buffer pool resizing operations.

  To avoid copying all buffer pool pages during resizing operations, the operation is performed in“chunks”. By default,innodb_buffer_pool_chunk_size is 128MB (134217728 bytes). The number of pages contained in a chunk depends on the value ofinnodb_page_size.innodb_buffer_pool_chunk_size can be increased or decreased in units of 1MB (1048576 bytes).

  The following conditions apply when altering theinnodb_buffer_pool_chunk_size value:

  • If innodb_buffer_pool_chunk_size *innodb_buffer_pool_instances is larger than the current buffer pool size when the buffer pool is initialized,innodb_buffer_pool_chunk_size is truncated toinnodb_buffer_pool_size /innodb_buffer_pool_instances.

  • Buffer pool size must always be equal to or a multiple ofinnodb_buffer_pool_chunk_size *innodb_buffer_pool_instances. If you alterinnodb_buffer_pool_chunk_size,innodb_buffer_pool_size is automatically rounded to a value that is equal to or a multiple ofinnodb_buffer_pool_chunk_size *innodb_buffer_pool_instances. The adjustment occurs when the buffer pool is initialized.

  Important

  Care should be taken when changinginnodb_buffer_pool_chunk_size, as changing this value can automatically increase the size of the buffer pool. Before changinginnodb_buffer_pool_chunk_size, calculate its effect oninnodb_buffer_pool_size to ensure that the resulting buffer pool size is acceptable.

  To avoid potential performance issues, the number of chunks (innodb_buffer_pool_size /innodb_buffer_pool_chunk_size) should not exceed 1000.

  Theinnodb_buffer_pool_size variable is dynamic, which permits resizing the buffer pool while the server is online. However, the buffer pool size must be equal to or a multiple ofinnodb_buffer_pool_chunk_size *innodb_buffer_pool_instances, and changing either of those variable settings requires restarting the server.

  SeeSection 17.8.3.1, “Configuring InnoDB Buffer Pool Size” for more information.

• innodb_buffer_pool_debug

  Command-Line Format	--innodb-buffer-pool-debug[={OFF|ON}]
  System Variable	innodb_buffer_pool_debug
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  Enabling this option permits multiple buffer pool instances when the buffer pool is less than 1GB in size, ignoring the 1GB minimum buffer pool size constraint imposed oninnodb_buffer_pool_instances. Theinnodb_buffer_pool_debug option is only available if debugging support is compiled in using theWITH_DEBUGCMake option.

• innodb_buffer_pool_dump_at_shutdown

  Command-Line Format	--innodb-buffer-pool-dump-at-shutdown[={OFF|ON}]
  System Variable	innodb_buffer_pool_dump_at_shutdown
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON

  Specifies whether to record the pages cached in theInnoDBbuffer pool when the MySQL server is shut down, to shorten thewarmup process at the next restart. Typically used in combination withinnodb_buffer_pool_load_at_startup. Theinnodb_buffer_pool_dump_pct option defines the percentage of most recently used buffer pool pages to dump.

  Bothinnodb_buffer_pool_dump_at_shutdown andinnodb_buffer_pool_load_at_startup are enabled by default.

  For more information, seeSection 17.8.3.6, “Saving and Restoring the Buffer Pool State”.

• innodb_buffer_pool_dump_now

  Command-Line Format	--innodb-buffer-pool-dump-now[={OFF|ON}]
  System Variable	innodb_buffer_pool_dump_now
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  Immediately makes a record of pages cached in theInnoDBbuffer pool. Typically used in combination withinnodb_buffer_pool_load_now.

  Enablinginnodb_buffer_pool_dump_now triggers the recording action but does not alter the variable setting, which always remainsOFF or0. To view buffer pool dump status after triggering a dump, query theInnodb_buffer_pool_dump_status variable.

  Enablinginnodb_buffer_pool_dump_now triggers the dump action but does not alter the variable setting, which always remainsOFF or0. To view buffer pool dump status after triggering a dump, query theInnodb_buffer_pool_dump_status variable.

  For more information, seeSection 17.8.3.6, “Saving and Restoring the Buffer Pool State”.

• innodb_buffer_pool_dump_pct

  Command-Line Format	--innodb-buffer-pool-dump-pct=#
  System Variable	innodb_buffer_pool_dump_pct
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	25
  Minimum Value	1
  Maximum Value	100

  Specifies the percentage of the most recently used pages for each buffer pool to read out and dump. The range is 1 to 100. The default value is 25. For example, if there are 4 buffer pools with 100 pages each, andinnodb_buffer_pool_dump_pct is set to 25, the 25 most recently used pages from each buffer pool are dumped.

• innodb_buffer_pool_filename

  Command-Line Format	--innodb-buffer-pool-filename=file_name
  System Variable	innodb_buffer_pool_filename
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	File name
  Default Value	ib_buffer_pool

  Specifies the name of the file that holds the list of tablespace IDs and page IDs produced byinnodb_buffer_pool_dump_at_shutdown orinnodb_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_pool and is located in theInnoDB data directory. A non-default location must be specified relative to the data directory.

  A file name can be specified at runtime, using aSET statement:

  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 orInnoDB returns a startup error indicating that there is no such file or directory.

  For more information, seeSection 17.8.3.6, “Saving and Restoring the Buffer Pool State”.

• innodb_buffer_pool_in_core_file

  Command-Line Format	--innodb-buffer-pool-in-core-file[={OFF|ON}]
  Introduced	8.0.14
  System Variable	innodb_buffer_pool_in_core_file
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON

  Disabling theinnodb_buffer_pool_in_core_file variable reduces the size of core files by excludingInnoDB buffer pool pages. To use this variable, thecore_file variable must be enabled and the operating system must support theMADV_DONTDUMP non-POSIX extension tomadvise(), which is supported in Linux 3.4 and later. For more information, seeSection 17.8.3.7, “Excluding Buffer Pool Pages from Core Files”.

• innodb_buffer_pool_instances

  Command-Line Format	--innodb-buffer-pool-instances=#
  System Variable	innodb_buffer_pool_instances
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value (Windows, 32-bit platforms)	see description
  Default Value (Other)	8 (or 1 if innodb_buffer_pool_size < 1GB)
  Minimum Value	1
  Maximum Value	64

  The number of regions that theInnoDBbuffer 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 poolmutex.

  This option only takes effect when settinginnodb_buffer_pool_size to 1GB or more. The total buffer pool size is divided among all the buffer pools. For best efficiency, specify a combination ofinnodb_buffer_pool_instances andinnodb_buffer_pool_size so that each buffer pool instance is at least 1GB.

  The default value on 32-bit Windows systems depends on the value ofinnodb_buffer_pool_size, as described below:

  • Ifinnodb_buffer_pool_size is greater than 1.3GB, the default forinnodb_buffer_pool_instances isinnodb_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 is 8 wheninnodb_buffer_pool_size is greater than or equal to 1GB. Otherwise, the default is 1.

  For related information, seeSection 17.8.3.1, “Configuring InnoDB Buffer Pool Size”.

• innodb_buffer_pool_load_abort

  Command-Line Format	--innodb-buffer-pool-load-abort[={OFF|ON}]
  System Variable	innodb_buffer_pool_load_abort
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  Interrupts the process of restoringInnoDBbuffer pool contents triggered byinnodb_buffer_pool_load_at_startup orinnodb_buffer_pool_load_now.

  Enablinginnodb_buffer_pool_load_abort triggers the abort action but does not alter the variable setting, which always remainsOFF or0. To view buffer pool load status after triggering an abort action, query theInnodb_buffer_pool_load_status variable.

  For more information, seeSection 17.8.3.6, “Saving and Restoring the Buffer Pool State”.

• innodb_buffer_pool_load_at_startup

  Command-Line Format	--innodb-buffer-pool-load-at-startup[={OFF|ON}]
  System Variable	innodb_buffer_pool_load_at_startup
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON

  Specifies that, on MySQL server startup, theInnoDBbuffer pool is automaticallywarmed up by loading the same pages it held at an earlier time. Typically used in combination withinnodb_buffer_pool_dump_at_shutdown.

  Bothinnodb_buffer_pool_dump_at_shutdown andinnodb_buffer_pool_load_at_startup are enabled by default.

  For more information, seeSection 17.8.3.6, “Saving and Restoring the Buffer Pool State”.

• innodb_buffer_pool_load_now

  Command-Line Format	--innodb-buffer-pool-load-now[={OFF|ON}]
  System Variable	innodb_buffer_pool_load_now
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  Immediatelywarms up theInnoDBbuffer pool by loading 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.

  Enablinginnodb_buffer_pool_load_now triggers the load action but does not alter the variable setting, which always remainsOFF or0. To view buffer pool load progress after triggering a load, query theInnodb_buffer_pool_load_status variable.

  For more information, seeSection 17.8.3.6, “Saving and Restoring the Buffer Pool State”.

• innodb_buffer_pool_size

  Command-Line Format	--innodb-buffer-pool-size=#
  System Variable	innodb_buffer_pool_size
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	134217728
  Minimum Value	5242880
  Maximum Value (64-bit platforms)	2**64-1
  Maximum Value (32-bit platforms)	2**32-1
  Unit	bytes

  The size in bytes of thebuffer pool, the memory area whereInnoDB caches 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_instances to 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.

  • InnoDB reserves 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. SeeSection 17.8.3.6, “Saving and Restoring the Buffer Pool State”.

  When you increase or decrease buffer pool size, the operation is performed in chunks. Chunk size is defined by theinnodb_buffer_pool_chunk_size variable, which has a default of 128 MB.

  Buffer pool size must always be equal to or a multiple ofinnodb_buffer_pool_chunk_size *innodb_buffer_pool_instances. If you alter the buffer pool size to a value that is not equal to or a multiple ofinnodb_buffer_pool_chunk_size *innodb_buffer_pool_instances, buffer pool size is automatically adjusted to a value that is equal to or a multiple ofinnodb_buffer_pool_chunk_size *innodb_buffer_pool_instances.

  innodb_buffer_pool_size can be set dynamically, which allows you to resize the buffer pool without restarting the server. TheInnodb_buffer_pool_resize_status status variable reports the status of online buffer pool resizing operations. SeeSection 17.8.3.1, “Configuring InnoDB Buffer Pool Size” for more information.

  If the server is started with--innodb-dedicated-server, theinnodb_buffer_pool_size value is determined automatically if it is not explicitly defined. For more information, seeSection 17.8.12, “Enabling Automatic InnoDB Configuration for a Dedicated MySQL Server”.

• innodb_change_buffer_max_size

  Command-Line Format	--innodb-change-buffer-max-size=#
  System Variable	innodb_change_buffer_max_size
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	25
  Minimum Value	0
  Maximum Value	50

  Maximum size for theInnoDBchange buffer, as a percentage of the total size of thebuffer 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, seeSection 17.5.2, “Change Buffer”. For general I/O tuning advice, seeSection 10.5.8, “Optimizing InnoDB Disk I/O”.

• innodb_change_buffering

  Command-Line Format	--innodb-change-buffering=value
  System Variable	innodb_change_buffering
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Enumeration
  Default Value	all
  Valid Values	none inserts deletes changes purges all

  WhetherInnoDB performschange 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. Values may also be specified numerically.

  Table 17.25 Permitted Values for innodb_change_buffering

  Value	Numeric Value	Description
  none	0	Do not buffer any operations.
  inserts	1	Buffer insert operations.
  deletes	2	Buffer delete marking operations; strictly speaking, the writes that mark index records for later deletion during a purge operation.
  changes	3	Buffer inserts and delete-marking operations.
  purges	4	Buffer the physical deletion operations that happen in the background.
  all	5	The default. Buffer inserts, delete-marking operations, and purges.

  
  

  For more information, seeSection 17.5.2, “Change Buffer”. For general I/O tuning advice, seeSection 10.5.8, “Optimizing InnoDB Disk I/O”.

• innodb_change_buffering_debug

  Command-Line Format	--innodb-change-buffering-debug=#
  System Variable	innodb_change_buffering_debug
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	0
  Minimum Value	0
  Maximum Value	2

  Sets a debug flag forInnoDB change buffering. A value of 1 forces all changes to the change buffer. A value of 2 causes an unexpected exit 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.

• innodb_checkpoint_disabled

  Command-Line Format	--innodb-checkpoint-disabled[={OFF|ON}]
  System Variable	innodb_checkpoint_disabled
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  This is a debug option that is only intended for expert debugging use. It disables checkpoints so that a deliberate server exit always initiatesInnoDB recovery. It should only be enabled for a short interval, typically before running DML operations that write redo log entries that would require recovery following a server exit. This option is only available if debugging support is compiled in using theWITH_DEBUGCMake option.

• innodb_checksum_algorithm

  Command-Line Format	--innodb-checksum-algorithm=value
  System Variable	innodb_checksum_algorithm
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Enumeration
  Default Value	crc32
  Valid Values	crc32 strict_crc32 innodb strict_innodb none strict_none

  Specifies how to generate and verify thechecksum stored in the disk blocks ofInnoDBtablespaces. The default value forinnodb_checksum_algorithm iscrc32.

  Versions ofMySQL 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 theMySQL Enterprise Backup 3.8.1 Change History for more information.

  The valueinnodb is backward-compatible with earlier versions of MySQL. The valuecrc32 uses 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 64 bits at a time, which is faster than theinnodb checksum algorithm, which scans blocks 8 bits at a time. The valuenone writes 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 thecrc32 algorithm, 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.

  The following table shows the difference between thenone,innodb, andcrc32 option values, and their strict counterparts.none,innodb, andcrc32 write 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 allInnoDB data files in an instance are created under an identicalinnodb_checksum_algorithm value.

  Table 17.26 Permitted innodb_checksum_algorithm Values

  Value	Generated checksum (when writing)	Permitted checksums (when reading)
  none	A constant number.	Any of the checksums generated bynone,innodb, orcrc32.
  innodb	A checksum calculated in software, using the original algorithm fromInnoDB.	Any of the checksums generated bynone,innodb, orcrc32.
  crc32	A checksum calculated using thecrc32 algorithm, possibly done with a hardware assist.	Any of the checksums generated bynone,innodb, orcrc32.
  strict_none	A constant number	Any of the checksums generated bynone,innodb, orcrc32.InnoDB prints an error message if a valid but non-matching checksum is encountered.
  strict_innodb	A checksum calculated in software, using the original algorithm fromInnoDB.	Any of the checksums generated bynone,innodb, orcrc32.InnoDB prints an error message if a valid but non-matching checksum is encountered.
  strict_crc32	A checksum calculated using thecrc32 algorithm, possibly done with a hardware assist.	Any of the checksums generated bynone,innodb, orcrc32.InnoDB prints an error message if a valid but non-matching checksum is encountered.

  
  

• innodb_cmp_per_index_enabled

  Command-Line Format	--innodb-cmp-per-index-enabled[={OFF|ON}]
  System Variable	innodb_cmp_per_index_enabled
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  Enables per-index compression-related statistics in the Information SchemaINNODB_CMP_PER_INDEX table. Because these statistics can be expensive to gather, only enable this option on development, test, or replica instances during performance tuning related toInnoDBcompressed tables.

  For more information, seeSection 28.4.8, “The INFORMATION_SCHEMA INNODB_CMP_PER_INDEX and INNODB_CMP_PER_INDEX_RESET Tables”, andSection 17.9.1.4, “Monitoring InnoDB Table Compression at Runtime”.

• innodb_commit_concurrency

  Command-Line Format	--innodb-commit-concurrency=#
  System Variable	innodb_commit_concurrency
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	0
  Minimum Value	0
  Maximum Value	1000

  The number ofthreads that cancommit at the same time. A value of 0 (the default) permits any number oftransactions to commit simultaneously.

  The value ofinnodb_commit_concurrency cannot be changed at runtime from zero to nonzero or vice versa. The value can be changed from one nonzero value to another.

• innodb_compress_debug

  Command-Line Format	--innodb-compress-debug=value
  System Variable	innodb_compress_debug
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Enumeration
  Default Value	none
  Valid Values	none zlib lz4 lz4hc

  Compresses all tables using a specified compression algorithm without having to define aCOMPRESSION attribute for each table. This option is only available if debugging support is compiled in using theWITH_DEBUGCMake option.

  For related information, seeSection 17.9.2, “InnoDB Page Compression”.

• innodb_compression_failure_threshold_pct

  Command-Line Format	--innodb-compression-failure-threshold-pct=#
  System Variable	innodb_compression_failure_threshold_pct
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	5
  Minimum Value	0
  Maximum Value	100

  Defines the compression failure rate threshold for a table, as a percentage, at which point MySQL begins adding padding withincompressed pages to avoid expensivecompression 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 byinnodb_compression_pad_pct_max. A value of zero disables the mechanism that monitors compression efficiency and dynamically adjusts the padding amount.

  For more information, seeSection 17.9.1.6, “Compression for OLTP Workloads”.

• innodb_compression_level

  Command-Line Format	--innodb-compression-level=#
  System Variable	innodb_compression_level
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	6
  Minimum Value	0
  Maximum Value	9

  Specifies the level of zlib compression to use forInnoDBcompressed 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, seeSection 17.9.1.6, “Compression for OLTP Workloads”.

• innodb_compression_pad_pct_max

  Command-Line Format	--innodb-compression-pad-pct-max=#
  System Variable	innodb_compression_pad_pct_max
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	50
  Minimum Value	0
  Maximum Value	75

  Specifies the maximum percentage that can be reserved as free space within each compressedpage, allowing room to reorganize the data and modification log within the page when acompressed table or index is updated and the data might be recompressed. Only applies wheninnodb_compression_failure_threshold_pct is set to a nonzero value, and the rate ofcompression failures passes the cutoff point.

  For more information, seeSection 17.9.1.6, “Compression for OLTP Workloads”.

• innodb_concurrency_tickets

  Command-Line Format	--innodb-concurrency-tickets=#
  System Variable	innodb_concurrency_tickets
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	5000
  Minimum Value	1
  Maximum Value	4294967295

  Determines the number ofthreads that can enterInnoDB concurrently. A thread is placed in a queue when it tries to enterInnoDB if 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 leaveInnoDB freely 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.

  With a smallinnodb_concurrency_tickets value, 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_tickets value 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 largeinnodb_concurrency_tickets value, 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_tickets value 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 nonzeroinnodb_thread_concurrency value, you may need to adjust theinnodb_concurrency_tickets value up or down to find the optimal balance between larger and smaller transactions. TheSHOW ENGINE INNODB STATUS report 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_TICKETS column of the Information SchemaINNODB_TRX table.

  For more information, seeSection 17.8.4, “Configuring Thread Concurrency for InnoDB”.

• innodb_data_file_path

  Command-Line Format	--innodb-data-file-path=file_name
  System Variable	innodb_data_file_path
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	String
  Default Value	ibdata1:12M:autoextend

  Defines the name, size, and attributes ofInnoDB system 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,autoextend attribute, andmax attribute:

  file_name:file_size[:autoextend[:max:max_file_size]]

  File sizes are specified in kilobytes, megabytes, or gigabytes by appendingK,M orG to 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, seeSystem Tablespace Data File Configuration. For resizing instructions, seeResizing the System Tablespace.

• innodb_data_home_dir

  Command-Line Format	--innodb-data-home-dir=dir_name
  System Variable	innodb_data_home_dir
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Directory name

  The common part of the directory path forInnoDBsystem tablespace data files. The default value is the MySQLdata directory. The setting is concatenated with theinnodb_data_file_path setting, unless that setting is defined with an absolute path.

  A trailing slash is required when specifying a value forinnodb_data_home_dir. For example:

  [mysqld]innodb_data_home_dir = /path/to/myibdata/

  This setting does not affect the location offile-per-table tablespaces.

  For related information, seeSection 17.8.1, “InnoDB Startup Configuration”.

• innodb_ddl_buffer_size

  Command-Line Format	--innodb-ddl-buffer-size=#
  Introduced	8.0.27
  System Variable	innodb_ddl_buffer_size
  Scope	Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	1048576
  Minimum Value	65536
  Maximum Value	4294967295
  Unit	bytes

  Defines the maximum buffer size for DDL operations. The default setting is 1048576 bytes (approximately 1 MB). Applies to online DDL operations that create or rebuild secondary indexes. SeeSection 17.12.4, “Online DDL Memory Management”. The maximum buffer size per DDL thread is the maximum buffer size divided by the number of DDL threads (innodb_ddl_buffer_size/innodb_ddl_threads).

• innodb_ddl_log_crash_reset_debug

  Command-Line Format	--innodb-ddl-log-crash-reset-debug[={OFF|ON}]
  System Variable	innodb_ddl_log_crash_reset_debug
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  Enable this debug option to reset DDL log crash injection counters to 1. This option is only available when debugging support is compiled in using theWITH_DEBUGCMake option.

• innodb_ddl_threads

  Command-Line Format	--innodb-ddl-threads=#
  Introduced	8.0.27
  System Variable	innodb_ddl_threads
  Scope	Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	4
  Minimum Value	1
  Maximum Value	64

  Defines the maximum number of parallel threads for the sort and build phases of index creation. Applies to online DDL operations that create or rebuild secondary indexes. For related information, seeSection 17.12.5, “Configuring Parallel Threads for Online DDL Operations”, andSection 17.12.4, “Online DDL Memory Management”.

• innodb_deadlock_detect

  Command-Line Format	--innodb-deadlock-detect[={OFF|ON}]
  System Variable	innodb_deadlock_detect
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON

  This option is used to disable deadlock detection. On high concurrency systems, deadlock detection can cause a slowdown when numerous threads wait for the same lock. At times, it may be more efficient to disable deadlock detection and rely on theinnodb_lock_wait_timeout setting for transaction rollback when a deadlock occurs.

  For related information, seeSection 17.7.5.2, “Deadlock Detection”.

• innodb_default_row_format

  Command-Line Format	--innodb-default-row-format=value
  System Variable	innodb_default_row_format
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Enumeration
  Default Value	DYNAMIC
  Valid Values	REDUNDANT COMPACT DYNAMIC

  Theinnodb_default_row_format option defines the default row format forInnoDB tables and user-created temporary tables. The default setting isDYNAMIC. Other permitted values areCOMPACT andREDUNDANT. TheCOMPRESSED row format, which is not supported for use in thesystem tablespace, cannot be defined as the default.

  Newly created tables use the row format defined byinnodb_default_row_format when aROW_FORMAT option is not specified explicitly or whenROW_FORMAT=DEFAULT is used.

  When aROW_FORMAT option is not specified explicitly or whenROW_FORMAT=DEFAULT is used, any operation that rebuilds a table also silently changes the row format of the table to the format defined byinnodb_default_row_format. For more information, seeDefining the Row Format of a Table.

  InternalInnoDB temporary tables created by the server to process queries use theDYNAMIC row format, regardless of theinnodb_default_row_format setting.

• innodb_directories

  Command-Line Format	--innodb-directories=dir_name
  System Variable	innodb_directories
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Directory name
  Default Value	NULL

  Defines directories to scan at startup for tablespace files. This option is used when moving or restoring tablespace files to a new location while the server is offline. It is also used to specify directories of tablespace files created using an absolute path or that reside outside of the data directory.

  Tablespace discovery during crash recovery relies on theinnodb_directories setting to identify tablespaces referenced in the redo logs. For more information, seeTablespace Discovery During Crash Recovery.

  The default value is NULL, but directories defined byinnodb_data_home_dir,innodb_undo_directory, anddatadir are always appended to theinnodb_directories argument value whenInnoDB builds a list of directories to scan at startup. These directories are appended regardless of whether aninnodb_directories setting is specified explicitly.

  innodb_directories may be specified as an option in a startup command or in a MySQL option file. Quotes surround the argument value because otherwise some command interpreters interpret semicolon (;) as a special character. (For example, Unix shells treat it as a command terminator.)

  Startup command:

  mysqld --innodb-directories="directory_path_1;directory_path_2"

  MySQL option file:

  [mysqld]innodb_directories="directory_path_1;directory_path_2"

  Wildcard expressions cannot be used to specify directories.

  Theinnodb_directories scan also traverses the subdirectories of specified directories. Duplicate directories and subdirectories are discarded from the list of directories to be scanned.

  For more information, seeSection 17.6.3.6, “Moving Tablespace Files While the Server is Offline”.

• innodb_disable_sort_file_cache

  Command-Line Format	--innodb-disable-sort-file-cache[={OFF|ON}]
  System Variable	innodb_disable_sort_file_cache
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  Disables the operating system file system cache for merge-sort temporary files. The effect is to open such files with the equivalent ofO_DIRECT.

• innodb_doublewrite

  Command-Line Format	--innodb-doublewrite=value (≥ 8.0.30) --innodb-doublewrite[={OFF|ON}] (≤ 8.0.29)
  System Variable	innodb_doublewrite
  Scope	Global
  Dynamic (≥ 8.0.30)	Yes
  Dynamic (≤ 8.0.29)	No
  SET_VAR Hint Applies	No
  Type (≥ 8.0.30)	Enumeration
  Type (≤ 8.0.29)	Boolean
  Default Value	ON
  Valid Values	ON OFF DETECT_AND_RECOVER DETECT_ONLY

  Theinnodb_doublewrite variable controls doublewrite buffering. Doublewrite buffering is enabled by default in most cases.

  Prior to MySQL 8.0.30, you can setinnodb_doublewrite toON orOFF when starting the server to enable or disable doublewrite buffering, respectively. From MySQL 8.0.30,innodb_doublewrite also supportsDETECT_AND_RECOVER andDETECT_ONLY settings.

  TheDETECT_AND_RECOVER setting is the same as theON setting. With this setting, the doublewrite buffer is fully enabled, with database page content written to the doublewrite buffer where it is accessed during recovery to fix incomplete page writes.

  With theDETECT_ONLY setting, only metadata is written to the doublewrite buffer. Database page content is not written to the doublewrite buffer, and recovery does not use the doublewrite buffer to fix incomplete page writes. This lightweight setting is intended for detecting incomplete page writes only.

  MySQL 8.0.30 onwards supports dynamic changes to theinnodb_doublewrite setting that enables the doublewrite buffer, betweenON,DETECT_AND_RECOVER, andDETECT_ONLY. MySQL does not support dynamic changes between a setting that enables the doublewrite buffer andOFF or vice versa.

  If the doublewrite buffer is located on a Fusion-io device that supports atomic writes, the doublewrite buffer is automatically disabled and data file writes are performed using Fusion-io atomic writes instead. However, be aware that theinnodb_doublewrite setting is global. When the doublewrite buffer is disabled, it is disabled for all data files including those that do not reside on Fusion-io hardware. This feature is only supported on Fusion-io hardware and is only enabled for Fusion-io NVMFS on Linux. To take full advantage of this feature, aninnodb_flush_method setting ofO_DIRECT is recommended.

  For related information, seeSection 17.6.4, “Doublewrite Buffer”.

• innodb_doublewrite_batch_size

  Command-Line Format	--innodb-doublewrite-batch-size=#
  Introduced	8.0.20
  System Variable	innodb_doublewrite_batch_size
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	0
  Minimum Value	0
  Maximum Value	256

  This variable was intended to represent the number of doublewrite pages to write in a batch. This functionality was replaced byinnodb_doublewrite_pages.

  For more information, seeSection 17.6.4, “Doublewrite Buffer”.

• innodb_doublewrite_dir

  Command-Line Format	--innodb-doublewrite-dir=dir_name
  Introduced	8.0.20
  System Variable	innodb_doublewrite_dir
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Directory name

  Defines the directory for doublewrite files. If no directory is specified, doublewrite files are created in theinnodb_data_home_dir directory, which defaults to the data directory if unspecified.

  For more information, seeSection 17.6.4, “Doublewrite Buffer”.

• innodb_doublewrite_files

  Command-Line Format	--innodb-doublewrite-files=#
  Introduced	8.0.20
  System Variable	innodb_doublewrite_files
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	innodb_buffer_pool_instances * 2
  Minimum Value	1
  Maximum Value	256

  Defines the number of doublewrite files. By default, two doublewrite files are created for each buffer pool instance.

  At a minimum, there are two doublewrite files. The maximum number of doublewrite files is two times the number of buffer pool instances. (The number of buffer pool instances is controlled by theinnodb_buffer_pool_instances variable.)

  For more information, seeSection 17.6.4, “Doublewrite Buffer”.

• innodb_doublewrite_pages

  Command-Line Format	--innodb-doublewrite-pages=#
  Introduced	8.0.20
  System Variable	innodb_doublewrite_pages
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	innodb_write_io_threads value
  Minimum Value	innodb_write_io_threads value
  Maximum Value	512

  Defines the maximum number of doublewrite pages per thread for a batch write. If no value is specified,innodb_doublewrite_pages is set to theinnodb_write_io_threads value.

  The default value changed from 4 (copied frominnodb_write_io_threads in 8.0) to 128 in MySQL 8.4.0. This small value could cause too many fsync operations for doublewrite operations. For related information, seeSection 10.5.8, “Optimizing InnoDB Disk I/O”.

  For more information, seeSection 17.6.4, “Doublewrite Buffer”.

• innodb_extend_and_initialize

  Command-Line Format	--innodb=extend-and-initialize[={OFF|ON}]
  Introduced	8.0.22
  System Variable	innodb_extend_and_initialize
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON

  Controls how space is allocated to file-per-table and general tablespaces on Linux systems.

  When enabled,InnoDB writes NULLs to newly allocated pages. When disabled, space is allocated usingposix_fallocate() calls, which reserve space without physically writing NULLs.

  For more information, seeSection 17.6.3.8, “Optimizing Tablespace Space Allocation on Linux”.

• innodb_fast_shutdown

  Command-Line Format	--innodb-fast-shutdown=#
  System Variable	innodb_fast_shutdown
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	1
  Valid Values	0 1 2

  TheInnoDBshutdown mode. If the value is 0,InnoDB does aslow shutdown, a fullpurge and a change buffer merge before shutting down. If the value is 1 (the default),InnoDB skips these operations at shutdown, a process known as afast shutdown. If the value is 2,InnoDB flushes its logs and shuts down cold, as if MySQL had crashed; no committed transactions are lost, but thecrash 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.

  Useinnodb_fast_shutdown=2 in emergency or troubleshooting situations, to get the absolute fastest shutdown if data is at risk of corruption.

• innodb_fil_make_page_dirty_debug

  Command-Line Format	--innodb-fil-make-page-dirty-debug=#
  System Variable	innodb_fil_make_page_dirty_debug
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	0
  Minimum Value	0
  Maximum Value	2**32-1

  By default, settinginnodb_fil_make_page_dirty_debug to the ID of a tablespace immediately dirties the first page of the tablespace. Ifinnodb_saved_page_number_debug is set to a non-default value, settinginnodb_fil_make_page_dirty_debug dirties the specified page. Theinnodb_fil_make_page_dirty_debug option is only available if debugging support is compiled in using theWITH_DEBUGCMake option.

• innodb_file_per_table

  Command-Line Format	--innodb-file-per-table[={OFF|ON}]
  System Variable	innodb_file_per_table
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON

  Wheninnodb_file_per_table is enabled, tables are created in file-per-table tablespaces by default. When disabled, tables are created in the system tablespace by default. For information about file-per-table tablespaces, seeSection 17.6.3.2, “File-Per-Table Tablespaces”. For information about theInnoDB system tablespace, seeSection 17.6.3.1, “The System Tablespace”.

  Theinnodb_file_per_table variable can be configured at runtime using aSET GLOBAL statement, specified on the command line at startup, or specified in an option file. Configuration at runtime requires privileges sufficient to set global system variables (seeSection 7.1.9.1, “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 forInnoDB data but is not returned to the operating system, as system tablespace data files never shrink.

  Theinnodb_file_per-table setting does not affect the creation of temporary tables. As of MySQL 8.0.14, temporary tables are created in session temporary tablespaces, and in the global temporary tablespace before that. SeeSection 17.6.3.5, “Temporary Tablespaces”.

• innodb_fill_factor

  Command-Line Format	--innodb-fill-factor=#
  System Variable	innodb_fill_factor
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	100
  Minimum Value	10
  Maximum Value	100

  InnoDB performs a bulk load when creating or rebuilding indexes. This method of index creation is known as a“sorted index build”.

  innodb_fill_factor defines the percentage of space on each B-tree page that is filled during a sorted index build, with the remaining space reserved for future index growth. For example, settinginnodb_fill_factor to 80 reserves 20 percent of the space on each B-tree page for future index growth. Actual percentages may vary. Theinnodb_fill_factor setting is interpreted as a hint rather than a hard limit.

  Aninnodb_fill_factor setting of 100 leaves 1/16 of the space in clustered index pages free for future index growth.

  innodb_fill_factor applies to both B-tree leaf and non-leaf pages. It does not apply to external pages used forTEXT orBLOB entries.

  For more information, seeSection 17.6.2.3, “Sorted Index Builds”.

• innodb_flush_log_at_timeout

  Command-Line Format	--innodb-flush-log-at-timeout=#
  System Variable	innodb_flush_log_at_timeout
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	1
  Minimum Value	1
  Maximum Value	2700
  Unit	seconds

  Write and flush the logs everyN seconds.innodb_flush_log_at_timeout allows the timeout period between flushes to be increased in order to reduce flushing and avoid impacting performance of binary log group commit. The default setting forinnodb_flush_log_at_timeout is once per second.

• innodb_flush_log_at_trx_commit

  Command-Line Format	--innodb-flush-log-at-trx-commit=#
  System Variable	innodb_flush_log_at_trx_commit
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Enumeration
  Default Value	1
  Valid Values	0 1 2

  Controls the balance between strictACID compliance forcommit 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 internalInnoDB activities that cause logs to be flushed independently of theinnodb_flush_log_at_trx_commit setting, 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 byinnodb_flush_log_at_timeout, which allows you to set log flushing frequency toN seconds (whereN is1 ... 2700, with a default value of 1). However, any unexpectedmysqld process exit can erase up toN seconds of transactions.

  • DDL changes and other internalInnoDB activities flush the log independently of theinnodb_flush_log_at_trx_commit setting.

  • InnoDBcrash recovery works regardless of theinnodb_flush_log_at_trx_commit setting. Transactions are either applied entirely or erased entirely.

  For durability and consistency in a replication setup that usesInnoDB with transactions:

  • If binary logging is enabled, setsync_binlog=1.

  • Always setinnodb_flush_log_at_trx_commit=1.

  For information on the combination of settings on a replica that is most resilient to unexpected halts, seeSection 19.4.2, “Handling an Unexpected Halt of a Replica”.

  Caution

  Many operating systems and some disk hardware fool the flush-to-disk operation. They may tellmysqld 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 corruptInnoDB data. 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.

• innodb_flush_method

  Command-Line Format	--innodb-flush-method=value
  System Variable	innodb_flush_method
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	String
  Default Value (Unix)	fsync
  Default Value (Windows)	unbuffered
  Valid Values (Unix)	fsync O_DSYNC littlesync nosync O_DIRECT O_DIRECT_NO_FSYNC
  Valid Values (Windows)	unbuffered normal

  Defines the method used toflush data toInnoDBdata files andlog files, which can affect I/O throughput.

  On Unix-like systems, the default value isfsync. On Windows, the default value isunbuffered.

  Note

  In MySQL 8.0,innodb_flush_method options can be specified numerically.

  Theinnodb_flush_method options for Unix-like systems include:

  • fsync or0:InnoDB uses thefsync() system call to flush both the data and log files.fsync is the default setting.

  • O_DSYNC or1:InnoDB usesO_SYNC to open and flush the log files, andfsync() to flush the data files.InnoDB does not useO_DSYNC directly because there have been problems with it on many varieties of Unix.

  • littlesync or2: This option is used for internal performance testing and is currently unsupported. Use at your own risk.

  • nosync or3: This option is used for internal performance testing and is currently unsupported. Use at your own risk.

  • O_DIRECT or4:InnoDB usesO_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:InnoDB usesO_DIRECT during flushing I/O, but skips thefsync() system call after each write operation.

    Prior to MySQL 8.0.14, this setting is not suitable for file systems such as XFS and EXT4, which require anfsync() 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_DIRECT instead.

    As of MySQL 8.0.14,fsync() is called after creating a new file, after increasing file size, and after closing a file, to ensure that file system metadata changes are synchronized. Thefsync() system call is still skipped after each write operation.

    Data loss is possible if redo log files and data files reside on different storage devices, and an unexpected exit occurs before data file writes are flushed from a device cache that is not battery-backed. If you use or intend to use different storage devices for redo log files and data files, and your data files reside on a device with a cache that is not battery-backed, useO_DIRECT instead.

  On platforms that supportfdatasync() system calls, theinnodb_use_fdatasync variable, introduced in MySQL 8.0.26, permitsinnodb_flush_method options that usefsync() to usefdatasync() instead. Anfdatasync() system call does not flush changes to file metadata unless required for subsequent data retrieval, providing a potential performance benefit.

  Theinnodb_flush_method options for Windows systems include:

  • unbuffered or0:InnoDB uses non-buffered I/O.

    Note

    Running MySQL server on a 4K sector hard drive on Windows is not supported withunbuffered. The workaround is to useinnodb_flush_method=normal.

  • normal or1:InnoDB uses buffered I/O.

  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 theInnodb_data_fsyncs status variable to see the overall number offsync() calls (orfdatasync() calls ifinnodb_use_fdatasync is enabled) 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_DIRECT can help to avoid double buffering between theInnoDB buffer pool and the operating system file system cache. On some systems whereInnoDB data and log files are located on a SAN, the default value orO_DSYNC might be faster for a read-heavy workload with mostlySELECT statements. Always test this parameter with hardware and workload that reflect your production environment. For general I/O tuning advice, seeSection 10.5.8, “Optimizing InnoDB Disk I/O”.

  If the server is started with--innodb-dedicated-server, the value ofinnodb_flush_method is set automatically if it is not explicitly defined. For more information, seeSection 17.8.12, “Enabling Automatic InnoDB Configuration for a Dedicated MySQL Server”.

• innodb_flush_neighbors

  Command-Line Format	--innodb-flush-neighbors=#
  System Variable	innodb_flush_neighbors
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Enumeration
  Default Value	0
  Valid Values	0 1 2

  Specifies whetherflushing a page from theInnoDBbuffer pool also flushes otherdirty pages in the sameextent.

  • A setting of 0 disablesinnodb_flush_neighbors. Dirty pages in the same extent are not flushed.

  • A 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 traditionalHDD storage device, flushing suchneighbor 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 onSSD, seek time is not a significant factor and you can set this option to 0 to spread out write operations. For related information, seeSection 17.8.3.5, “Configuring Buffer Pool Flushing”.

• innodb_flush_sync

  Command-Line Format	--innodb-flush-sync[={OFF|ON}]
  System Variable	innodb_flush_sync
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON

  Theinnodb_flush_sync variable, which is enabled by default, causes theinnodb_io_capacity andinnodb_io_capacity_max settings to be ignored during bursts of I/O activity that occur atcheckpoints. To adhere to the I/O rate defined byinnodb_io_capacity andinnodb_io_capacity_max, disableinnodb_flush_sync.

  For information about configuring theinnodb_flush_sync variable, seeSection 17.8.7, “Configuring InnoDB I/O Capacity”.

• innodb_flushing_avg_loops

  Command-Line Format	--innodb-flushing-avg-loops=#
  System Variable	innodb_flushing_avg_loops
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	30
  Minimum Value	1
  Maximum Value	1000

  Number of iterations for whichInnoDB keeps the previously calculated snapshot of the flushing state, controlling how quicklyadaptive flushing responds to changingworkloads. Increasing the value makes the rate offlush 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, seeSection 17.8.3.5, “Configuring Buffer Pool Flushing”.

• innodb_force_load_corrupted

  Command-Line Format	--innodb-force-load-corrupted[={OFF|ON}]
  System Variable	innodb_force_load_corrupted
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  PermitsInnoDB to 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.

• innodb_force_recovery

  Command-Line Format	--innodb-force-recovery=#
  System Variable	innodb_force_recovery
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	0
  Minimum Value	0
  Maximum Value	6

  Thecrash 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 aboutinnodb_force_recovery, seeSection 17.21.3, “Forcing InnoDB Recovery”.

  Warning

  Only set this variable to a value greater than 0 in an emergency situation so that you can startInnoDB and dump your tables. As a safety measure,InnoDB preventsINSERT,UPDATE, orDELETE operations wheninnodb_force_recovery is greater than 0. Aninnodb_force_recovery setting of 4 or greater placesInnoDB into read-only mode.

  These restrictions may cause replication administration commands to fail with an error, as replication stores the replica status logs inInnoDB tables.

• innodb_fsync_threshold

  Command-Line Format	--innodb-fsync-threshold=#
  Introduced	8.0.13
  System Variable	innodb_fsync_threshold
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	0
  Minimum Value	0
  Maximum Value	2**64-1

  By default, whenInnoDB creates a new data file, such as a new log file or tablespace file, the file is fully written to the operating system cache before it is flushed to disk, which can cause a large amount of disk write activity to occur at once. To force smaller, periodic flushes of data from the operating system cache, you can use theinnodb_fsync_threshold variable to define a threshold value, in bytes. When the byte threshold is reached, the contents of the operating system cache are flushed to disk. The default value of 0 forces the default behavior, which is to flush data to disk only after a file is fully written to the cache.

  Specifying a threshold to force smaller, periodic flushes may be beneficial in cases where multiple MySQL instances use the same storage devices. For example, creating a new MySQL instance and its associated data files could cause large surges of disk write activity, impeding the performance of other MySQL instances that use the same storage devices. Configuring a threshold helps avoid such surges in write activity.

• innodb_ft_aux_table

  System Variable	innodb_ft_aux_table
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	String

  Specifies the qualified name of anInnoDB table containing aFULLTEXT index. 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 formatdb_name/table_name, theINFORMATION_SCHEMA tablesINNODB_FT_INDEX_TABLE,INNODB_FT_INDEX_CACHE,INNODB_FT_CONFIG,INNODB_FT_DELETED, andINNODB_FT_BEING_DELETED show information about the search index for the specified table.

  For more information, seeSection 17.15.4, “InnoDB INFORMATION_SCHEMA FULLTEXT Index Tables”.

• innodb_ft_cache_size

  Command-Line Format	--innodb-ft-cache-size=#
  System Variable	innodb_ft_cache_size
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	8000000
  Minimum Value	1600000
  Maximum Value	80000000
  Unit	bytes

  The memory allocated, in bytes, for theInnoDBFULLTEXT search index cache, which holds a parsed document in memory while creating anInnoDBFULLTEXT index. Index inserts and updates are only committed to disk when theinnodb_ft_cache_size size limit is reached.innodb_ft_cache_size defines the cache size on a per table basis. To set a global limit for all tables, seeinnodb_ft_total_cache_size.

  For more information, seeInnoDB Full-Text Index Cache.

• innodb_ft_enable_diag_print

  Command-Line Format	--innodb-ft-enable-diag-print[={OFF|ON}]
  System Variable	innodb_ft_enable_diag_print
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  Whether to enable additional full-text search (FTS) diagnostic output. This option is primarily intended for advanced FTS debugging and is not 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 bytesSYNC words: 100

  • FTS optimize progress. For example:

    FTS start optimize testFTS_OPTIMIZE: optimize "mysql"FTS_OPTIMIZE: processed "mysql"

  • FTS index build progress. For example:

    Number of doc processed: 1000

  • For 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) 10000Full Search Memory: 245666 (bytes),  Row: 10000

• innodb_ft_enable_stopword

  Command-Line Format	--innodb-ft-enable-stopword[={OFF|ON}]
  System Variable	innodb_ft_enable_stopword
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON

  Specifies that a set ofstopwords is associated with anInnoDBFULLTEXT index at the time the index is created. If theinnodb_ft_user_stopword_table option is set, the stopwords are taken from that table. Else, if theinnodb_ft_server_stopword_table option is set, the stopwords are taken from that table. Otherwise, a built-in set of default stopwords is used.

  For more information, seeSection 14.9.4, “Full-Text Stopwords”.

• innodb_ft_max_token_size

  Command-Line Format	--innodb-ft-max-token-size=#
  System Variable	innodb_ft_max_token_size
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	84
  Minimum Value	10
  Maximum Value	84

  Maximum character length of words that are stored in anInnoDBFULLTEXT index. 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, seeSection 14.9.6, “Fine-Tuning MySQL Full-Text Search”.

• innodb_ft_min_token_size

  Command-Line Format	--innodb-ft-min-token-size=#
  System Variable	innodb_ft_min_token_size
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	3
  Minimum Value	0
  Maximum Value	16

  Minimum length of words that are stored in anInnoDBFULLTEXT index. 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, seeSection 14.9.6, “Fine-Tuning MySQL Full-Text Search”.

• innodb_ft_num_word_optimize

  Command-Line Format	--innodb-ft-num-word-optimize=#
  System Variable	innodb_ft_num_word_optimize
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	2000
  Minimum Value	1000
  Maximum Value	10000

  Number of words to process during eachOPTIMIZE TABLE operation on anInnoDBFULLTEXT index. 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 TABLE statements, each picking up where the last left off.

  For more information, seeSection 14.9.6, “Fine-Tuning MySQL Full-Text Search”.

• innodb_ft_result_cache_limit

  Command-Line Format	--innodb-ft-result-cache-limit=#
  System Variable	innodb_ft_result_cache_limit
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	2000000000
  Minimum Value	1000000
  Maximum Value	2**32-1
  Unit	bytes

  TheInnoDB full-text search query result cache limit (defined in bytes) per full-text search query or per thread. Intermediate and finalInnoDB full-text search query results are handled in memory. Useinnodb_ft_result_cache_limit to place a size limit on the full-text search query result cache to avoid excessive memory consumption in case of very largeInnoDB full-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.

  The maximum value ofinnodb_ft_result_cache_limit for all platform types and bit sizes is 2**32-1.

• innodb_ft_server_stopword_table

  Command-Line Format	--innodb-ft-server-stopword-table=db_name/table_name
  System Variable	innodb_ft_server_stopword_table
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	String
  Default Value	NULL

  This option is used to specify your ownInnoDBFULLTEXT index stopword list for allInnoDB tables. To configure your own stopword list for a specificInnoDB table, useinnodb_ft_user_stopword_table.

  Setinnodb_ft_server_stopword_table to the name of the table containing a list of stopwords, in the formatdb_name/table_name.

  The stopword table must exist before you configureinnodb_ft_server_stopword_table.innodb_ft_enable_stopword must be enabled andinnodb_ft_server_stopword_table option must be configured before you create theFULLTEXT index.

  The stopword table must be anInnoDB table, containing a singleVARCHAR column namedvalue.

  For more information, seeSection 14.9.4, “Full-Text Stopwords”.

• innodb_ft_sort_pll_degree

  Command-Line Format	--innodb-ft-sort-pll-degree=#
  System Variable	innodb_ft_sort_pll_degree
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	2
  Minimum Value	1
  Maximum Value	16

  Number of threads used in parallel to index and tokenize text in anInnoDBFULLTEXT index when building asearch index.

  For related information, seeSection 17.6.2.4, “InnoDB Full-Text Indexes”, andinnodb_sort_buffer_size.

• innodb_ft_total_cache_size

  Command-Line Format	--innodb-ft-total-cache-size=#
  System Variable	innodb_ft_total_cache_size
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	640000000
  Minimum Value	32000000
  Maximum Value	1600000000
  Unit	bytes

  The total memory allocated, in bytes, for theInnoDB full-text search index cache for all tables. Creating numerous tables, each with aFULLTEXT search index, could consume a significant portion of available memory.innodb_ft_total_cache_size defines 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, seeInnoDB Full-Text Index Cache.

• innodb_ft_user_stopword_table

  Command-Line Format	--innodb-ft-user-stopword-table=db_name/table_name
  System Variable	innodb_ft_user_stopword_table
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	String
  Default Value	NULL

  This option is used to specify your ownInnoDBFULLTEXT index stopword list on a specific table. To configure your own stopword list for allInnoDB tables, useinnodb_ft_server_stopword_table.

  Setinnodb_ft_user_stopword_table to the name of the table containing a list of stopwords, in the formatdb_name/table_name.

  The stopword table must exist before you configureinnodb_ft_user_stopword_table.innodb_ft_enable_stopword must be enabled andinnodb_ft_user_stopword_table must be configured before you create theFULLTEXT index.

  The stopword table must be anInnoDB table, containing a singleVARCHAR column namedvalue.

  For more information, seeSection 14.9.4, “Full-Text Stopwords”.

• innodb_idle_flush_pct

  Command-Line Format	--innodb-idle-flush-pct=#
  Introduced	8.0.18
  System Variable	innodb_idle_flush_pct
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	100
  Minimum Value	0
  Maximum Value	100

  Limits page flushing whenInnoDB is idle. Theinnodb_idle_flush_pct value is a percentage of theinnodb_io_capacity setting, which defines the number of I/O operations per second available toInnoDB. For more information, seeLimiting Buffer Flushing During Idle Periods.

• innodb_io_capacity

  Command-Line Format	--innodb-io-capacity=#
  System Variable	innodb_io_capacity
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	200
  Minimum Value	100
  Maximum Value (64-bit platforms, ≤ 8.0.37)	2**64-1
  Maximum Value	2**32-1

  Theinnodb_io_capacity variable defines the number of I/O operations per second (IOPS) available toInnoDB background tasks, such asflushing pages from thebuffer pool and merging data from thechange buffer.

  For information about configuring theinnodb_io_capacity variable, seeSection 17.8.7, “Configuring InnoDB I/O Capacity”.

• innodb_io_capacity_max

  Command-Line Format	--innodb-io-capacity-max=#
  System Variable	innodb_io_capacity_max
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	2 * innodb_io_capacity, min of 2000
  Minimum Value	100
  Maximum Value (Unix, 64-bit platforms, ≤ 8.0.28)	2**64-1
  Maximum Value (Other)	2**32-1

  If flushing activity falls behind,InnoDB can flush more aggressively, at a higher rate of I/O operations per second (IOPS) than defined by theinnodb_io_capacity variable. Theinnodb_io_capacity_max variable defines a maximum number of IOPS performed byInnoDB background tasks in such situations. This option does not controlinnodb_flush_sync behavior.

  For information about configuring theinnodb_io_capacity_max variable, seeSection 17.8.7, “Configuring InnoDB I/O Capacity”.

• innodb_limit_optimistic_insert_debug

  Command-Line Format	--innodb-limit-optimistic-insert-debug=#
  System Variable	innodb_limit_optimistic_insert_debug
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	0
  Minimum Value	0
  Maximum Value	2**32-1

  Limits the number of records perB-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 theWITH_DEBUGCMake option.

• innodb_lock_wait_timeout

  Command-Line Format	--innodb-lock-wait-timeout=#
  System Variable	innodb_lock_wait_timeout
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	50
  Minimum Value	1
  Maximum Value	1073741824
  Unit	seconds

  The length of time in seconds anInnoDBtransaction waits for arow lock before giving up. The default value is 50 seconds. A transaction that tries to access a row that is locked by anotherInnoDB transaction 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 transaction

  When a lock wait timeout occurs, the current statement isrolled back (not the entire transaction). To have the entire transaction roll back, start the server with the--innodb-rollback-on-timeout option. See alsoSection 17.21.5, “InnoDB Error Handling”.

  You might decrease this value for highly interactive applications orOLTP 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_timeout applies toInnoDB row locks. A MySQLtable lock does not happen insideInnoDB and this timeout does not apply to waits for table locks.

  The lock wait timeout value does not apply todeadlocks wheninnodb_deadlock_detect is enabled (the default) becauseInnoDB detects deadlocks immediately and rolls back one of the deadlocked transactions. Wheninnodb_deadlock_detect is disabled,InnoDB relies oninnodb_lock_wait_timeout for transaction rollback when a deadlock occurs. SeeSection 17.7.5.2, “Deadlock Detection”.

  innodb_lock_wait_timeout can be set at runtime with theSET GLOBAL orSET SESSION statement. Changing theGLOBAL setting requires privileges sufficient to set global system variables (seeSection 7.1.9.1, “System Variable Privileges”) and affects the operation of all clients that subsequently connect. Any client can change theSESSION setting forinnodb_lock_wait_timeout, which affects only that client.

• innodb_log_buffer_size

  Command-Line Format	--innodb-log-buffer-size=#
  System Variable	innodb_log_buffer_size
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	16777216
  Minimum Value	1048576
  Maximum Value	4294967295

  The size in bytes of the buffer thatInnoDB uses to write to thelog files on disk. The default is 16MB. A largelog buffer enables largetransactions to run without the need to write the log to disk before the transactionscommit. Thus, if you have transactions that update, insert, or delete many rows, making the log buffer larger saves disk I/O. For related information, seeMemory Configuration, andSection 10.5.4, “Optimizing InnoDB Redo Logging”. For general I/O tuning advice, seeSection 10.5.8, “Optimizing InnoDB Disk I/O”.

• innodb_log_checkpoint_fuzzy_now

  Command-Line Format	--innodb-log-checkpoint-fuzzy-now[={OFF|ON}]
  Introduced	8.0.13
  System Variable	innodb_log_checkpoint_fuzzy_now
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  Enable this debug option to forceInnoDB to write a fuzzy checkpoint. This option is only available if debugging support is compiled in using theWITH_DEBUGCMake option.

• innodb_log_checkpoint_now

  Command-Line Format	--innodb-log-checkpoint-now[={OFF|ON}]
  System Variable	innodb_log_checkpoint_now
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  Enable this debug option to forceInnoDB to write a checkpoint. This option is only available if debugging support is compiled in using theWITH_DEBUGCMake option.

• innodb_log_checksums

  Command-Line Format	--innodb-log-checksums[={OFF|ON}]
  System Variable	innodb_log_checksums
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON

  Enables or disables checksums for redo log pages.

  innodb_log_checksums=ON enables theCRC-32C checksum algorithm for redo log pages. Wheninnodb_log_checksums is disabled, the contents of the redo log page checksum field are ignored.

  Checksums on the redo log header page and redo log checkpoint pages are never disabled.

• innodb_log_compressed_pages

  Command-Line Format	--innodb-log-compressed-pages[={OFF|ON}]
  System Variable	innodb_log_compressed_pages
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON

  Specifies whether images ofre-compressedpages are written to theredo log. Re-compression may occur when changes are made to compressed data.

  innodb_log_compressed_pages is enabled by default to prevent corruption that could occur if a different version of thezlib compression algorithm is used during recovery. If you are certain that thezlib version is not subject to change, you can disableinnodb_log_compressed_pages to reduce redo log generation for workloads that modify compressed data.

  To measure the effect of enabling or disablinginnodb_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 theLOG section ofSHOW ENGINE INNODB STATUS output, or monitoringInnodb_os_log_written status for the number of bytes written to the redo log files.

  For related information, seeSection 17.9.1.6, “Compression for OLTP Workloads”.

• innodb_log_file_size

  Command-Line Format	--innodb-log-file-size=#
  Deprecated	8.0.30
  System Variable	innodb_log_file_size
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	50331648
  Minimum Value	4194304
  Maximum Value	512GB / innodb_log_files_in_group
  Unit	bytes

  Note

  innodb_log_file_size andinnodb_log_files_in_group are deprecated in MySQL 8.0.30. These variables are superseded byinnodb_redo_log_capacity. For more information, seeSection 17.6.5, “Redo Log”.

  The size in bytes of eachlog file in alog 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 makecrash recovery slower.

  The minimuminnodb_log_file_size is 4MB.

  For related information, seeRedo Log Configuration. For general I/O tuning advice, seeSection 10.5.8, “Optimizing InnoDB Disk I/O”.

  If the server is started with--innodb-dedicated-server, the value ofinnodb_log_file_size is set automatically if it is not explicitly defined. For more information, seeSection 17.8.12, “Enabling Automatic InnoDB Configuration for a Dedicated MySQL Server”.

• innodb_log_files_in_group

  Command-Line Format	--innodb-log-files-in-group=#
  Deprecated	8.0.30
  System Variable	innodb_log_files_in_group
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	2
  Minimum Value	2
  Maximum Value	100

  Note

  innodb_log_file_size andinnodb_log_files_in_group are deprecated in MySQL 8.0.30. These variables are superseded byinnodb_redo_log_capacity. For more information, seeSection 17.6.5, “Redo Log”.

  The number oflog files in thelog group.InnoDB writes 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, seeRedo Log Configuration.

  If the server is started with--innodb-dedicated-server, the value ofinnodb_log_files_in_group is set automatically if it is not explicitly defined. For more information, seeSection 17.8.12, “Enabling Automatic InnoDB Configuration for a Dedicated MySQL Server”.

• innodb_log_group_home_dir

  Command-Line Format	--innodb-log-group-home-dir=dir_name
  System Variable	innodb_log_group_home_dir
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Directory name

  The directory path to theInnoDBredo log files.

  For related information, seeRedo Log Configuration.

• innodb_log_spin_cpu_abs_lwm

  Command-Line Format	--innodb-log-spin-cpu-abs-lwm=#
  System Variable	innodb_log_spin_cpu_abs_lwm
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	80
  Minimum Value	0
  Maximum Value	4294967295

  Defines the minimum amount of CPU usage below which user threads no longer spin while waiting for flushed redo. The value is expressed as a sum of CPU core usage. For example, The default value of 80 is 80% of a single CPU core. On a system with a multi-core processor, a value of 150 represents 100% usage of one CPU core plus 50% usage of a second CPU core.

  For related information, seeSection 10.5.4, “Optimizing InnoDB Redo Logging”.

• innodb_log_spin_cpu_pct_hwm

  Command-Line Format	--innodb-log-spin-cpu-pct-hwm=#
  System Variable	innodb_log_spin_cpu_pct_hwm
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	50
  Minimum Value	0
  Maximum Value	100

  Defines the maximum amount of CPU usage above which user threads no longer spin while waiting for flushed redo. The value is expressed as a percentage of the combined total processing power of all CPU cores. The default value is 50%. For example, 100% usage of two CPU cores is 50% of the combined CPU processing power on a server with four CPU cores.

  Theinnodb_log_spin_cpu_pct_hwm variable respects processor affinity. For example, if a server has 48 cores but themysqld process is pinned to only four CPU cores, the other 44 CPU cores are ignored.

  For related information, seeSection 10.5.4, “Optimizing InnoDB Redo Logging”.

• innodb_log_wait_for_flush_spin_hwm

  Command-Line Format	--innodb-log-wait-for-flush-spin-hwm=#
  System Variable	innodb_log_wait_for_flush_spin_hwm
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	400
  Minimum Value	0
  Maximum Value (64-bit platforms, ≤ 8.0.37)	2**64-1
  Maximum Value	2**32-1
  Unit	microseconds

  Defines the maximum average log flush time beyond which user threads no longer spin while waiting for flushed redo. The default value is 400 microseconds.

  For related information, seeSection 10.5.4, “Optimizing InnoDB Redo Logging”.

• innodb_log_write_ahead_size

  Command-Line Format	--innodb-log-write-ahead-size=#
  System Variable	innodb_log_write_ahead_size
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	8192
  Minimum Value	512 (log file block size)
  Maximum Value	Equal to innodb_page_size
  Unit	bytes

  Defines the write-ahead block size for the redo log, in bytes. To avoid“read-on-write”, setinnodb_log_write_ahead_size to match the operating system or file system cache block size. The default setting is 8192 bytes. Read-on-write occurs when redo log blocks are not entirely cached to the operating system or file system due to a mismatch between write-ahead block size for the redo log and operating system or file system cache block size.

  Valid values forinnodb_log_write_ahead_size are multiples of theInnoDB log file block size (2ⁿ). The minimum value is theInnoDB log file block size (512). Write-ahead does not occur when the minimum value is specified. The maximum value is equal to theinnodb_page_size value. If you specify a value forinnodb_log_write_ahead_size that is larger than theinnodb_page_size value, theinnodb_log_write_ahead_size setting is truncated to theinnodb_page_size value.

  Setting theinnodb_log_write_ahead_size value too low in relation to the operating system or file system cache block size results in“read-on-write”. Setting the value too high may have a slight impact onfsync performance for log file writes due to several blocks being written at once.

  For related information, seeSection 10.5.4, “Optimizing InnoDB Redo Logging”.

• innodb_log_writer_threads

  Command-Line Format	--innodb-log-writer-threads[={OFF|ON}]
  Introduced	8.0.22
  System Variable	innodb_log_writer_threads
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON

  Enables dedicated log writer threads for writing redo log records from the log buffer to the system buffers and flushing the system buffers to the redo log files. Dedicated log writer threads can improve performance on high-concurrency systems, but for low-concurrency systems, disabling dedicated log writer threads provides better performance.

  For more information, seeSection 10.5.4, “Optimizing InnoDB Redo Logging”.

• innodb_lru_scan_depth

  Command-Line Format	--innodb-lru-scan-depth=#
  System Variable	innodb_lru_scan_depth
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	1024
  Minimum Value	100
  Maximum Value (64-bit platforms, ≤ 8.0.37)	2**64-1
  Maximum Value	2**32-1

  A parameter that influences the algorithms and heuristics for theflush operation for theInnoDBbuffer 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 fordirty 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 tuninginnodb_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_depth when changing the number of buffer pool instances, sinceinnodb_lru_scan_depth *innodb_buffer_pool_instances defines the amount of work performed by the page cleaner thread each second.

  For related information, seeSection 17.8.3.5, “Configuring Buffer Pool Flushing”. For general I/O tuning advice, seeSection 10.5.8, “Optimizing InnoDB Disk I/O”.

• innodb_max_dirty_pages_pct

  Command-Line Format	--innodb-max-dirty-pages-pct=#
  System Variable	innodb_max_dirty_pages_pct
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Numeric
  Default Value	90
  Minimum Value	0
  Maximum Value	99.999

  InnoDB tries toflush data from thebuffer pool so that the percentage ofdirty pages does not exceed this value.

  Theinnodb_max_dirty_pages_pct setting establishes a target for flushing activity. It does not affect the rate of flushing. For information about managing the rate of flushing, seeSection 17.8.3.5, “Configuring Buffer Pool Flushing”.

  For related information, seeSection 17.8.3.5, “Configuring Buffer Pool Flushing”. For general I/O tuning advice, seeSection 10.5.8, “Optimizing InnoDB Disk I/O”.

• innodb_max_dirty_pages_pct_lwm

  Command-Line Format	--innodb-max-dirty-pages-pct-lwm=#
  System Variable	innodb_max_dirty_pages_pct_lwm
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Numeric
  Default Value	10
  Minimum Value	0
  Maximum Value	99.999

  Defines a low water mark representing the percentage ofdirty pages at which preflushing is enabled to control the dirty page ratio. A value of 0 disables the pre-flushing behavior entirely. The configured value should always be lower than theinnodb_max_dirty_pages_pct value. For more information, seeSection 17.8.3.5, “Configuring Buffer Pool Flushing”.

• innodb_max_purge_lag

  Command-Line Format	--innodb-max-purge-lag=#
  System Variable	innodb_max_purge_lag
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	0
  Minimum Value	0
  Maximum Value	4294967295

  Defines the desired maximum purge lag. If this value is exceeded, a delay is imposed onINSERT,UPDATE, andDELETE operations 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, seeSection 17.8.9, “Purge Configuration”.

• innodb_max_purge_lag_delay

  Command-Line Format	--innodb-max-purge-lag-delay=#
  System Variable	innodb_max_purge_lag_delay
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	0
  Minimum Value	0
  Maximum Value	10000000
  Unit	microseconds

  Specifies the maximum delay in microseconds for the delay imposed when theinnodb_max_purge_lag threshold is exceeded. The specifiedinnodb_max_purge_lag_delay value is an upper limit on the delay period calculated by theinnodb_max_purge_lag formula.

  For more information, seeSection 17.8.9, “Purge Configuration”.

• innodb_max_undo_log_size

  Command-Line Format	--innodb-max-undo-log-size=#
  System Variable	innodb_max_undo_log_size
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	1073741824
  Minimum Value	10485760
  Maximum Value	2**64-1
  Unit	bytes

  Defines a threshold size for undo tablespaces. If an undo tablespace exceeds the threshold, it can be marked for truncation wheninnodb_undo_log_truncate is enabled. The default value is 1073741824 bytes (1024 MiB).

  For more information, seeTruncating Undo Tablespaces.

• innodb_merge_threshold_set_all_debug

  Command-Line Format	--innodb-merge-threshold-set-all-debug=#
  System Variable	innodb_merge_threshold_set_all_debug
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	50
  Minimum Value	1
  Maximum Value	50

  Defines a page-full percentage value for index pages that overrides the currentMERGE_THRESHOLD setting for all indexes that are currently in the dictionary cache. This option is only available if debugging support is compiled in using theWITH_DEBUGCMake option. For related information, seeSection 17.8.11, “Configuring the Merge Threshold for Index Pages”.

• innodb_monitor_disable

  Command-Line Format	--innodb-monitor-disable={counter|module|pattern|all}
  System Variable	innodb_monitor_disable
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	String

  This variable acts as a switch, disablingInnoDBmetrics counters. Counter data may be queried using the Information SchemaINNODB_METRICS table. For usage information, seeSection 17.15.6, “InnoDB INFORMATION_SCHEMA Metrics Table”.

  innodb_monitor_disable='latch' disables statistics collection forSHOW ENGINE INNODB MUTEX. For more information, seeSection 15.7.7.15, “SHOW ENGINE Statement”.

• innodb_monitor_enable

  Command-Line Format	--innodb-monitor-enable={counter|module|pattern|all}
  System Variable	innodb_monitor_enable
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	String

  This variable acts as a switch, enablingInnoDBmetrics counters. Counter data may be queried using the Information SchemaINNODB_METRICS table. For usage information, seeSection 17.15.6, “InnoDB INFORMATION_SCHEMA Metrics Table”.

  innodb_monitor_enable='latch' enables statistics collection forSHOW ENGINE INNODB MUTEX. For more information, seeSection 15.7.7.15, “SHOW ENGINE Statement”.

• innodb_monitor_reset

  Command-Line Format	--innodb-monitor-reset={counter|module|pattern|all}
  System Variable	innodb_monitor_reset
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Enumeration
  Default Value	NULL
  Valid Values	counter module pattern all

  This variable acts as a switch, resetting the count value forInnoDBmetrics counters to zero. Counter data may be queried using the Information SchemaINNODB_METRICS table. For usage information, seeSection 17.15.6, “InnoDB INFORMATION_SCHEMA Metrics Table”.

  innodb_monitor_reset='latch' resets statistics reported bySHOW ENGINE INNODB MUTEX. For more information, seeSection 15.7.7.15, “SHOW ENGINE Statement”.

• innodb_monitor_reset_all

  Command-Line Format	--innodb-monitor-reset-all={counter|module|pattern|all}
  System Variable	innodb_monitor_reset_all
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Enumeration
  Default Value	NULL
  Valid Values	counter module pattern all

  This variable acts as a switch, resetting all values (minimum, maximum, and so on) forInnoDBmetrics counters. Counter data may be queried using the Information SchemaINNODB_METRICS table. For usage information, seeSection 17.15.6, “InnoDB INFORMATION_SCHEMA Metrics Table”.

• innodb_numa_interleave

  Command-Line Format	--innodb-numa-interleave[={OFF|ON}]
  System Variable	innodb_numa_interleave
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  Enables the NUMA interleave memory policy for allocation of theInnoDB buffer pool. Wheninnodb_numa_interleave is enabled, the NUMA memory policy is set toMPOL_INTERLEAVE for themysqld process. After theInnoDB buffer pool is allocated, the NUMA memory policy is set back toMPOL_DEFAULT. For theinnodb_numa_interleave option to be available, MySQL must be compiled on a NUMA-enabled Linux system.

  CMake sets the defaultWITH_NUMA value based on whether the current platform hasNUMA support. For more information, seeSection 2.8.7, “MySQL Source-Configuration Options”.

• innodb_old_blocks_pct

  Command-Line Format	--innodb-old-blocks-pct=#
  System Variable	innodb_old_blocks_pct
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	37
  Minimum Value	5
  Maximum Value	95

  Specifies the approximate percentage of theInnoDBbuffer pool used for the old blocksublist. 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, seeSection 17.8.3.3, “Making the Buffer Pool Scan Resistant”. For information about buffer pool management, theLRU algorithm, andeviction policies, seeSection 17.5.1, “Buffer Pool”.

• innodb_old_blocks_time

  Command-Line Format	--innodb-old-blocks-time=#
  System Variable	innodb_old_blocks_time
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	1000
  Minimum Value	0
  Maximum Value	2**32-1
  Unit	milliseconds

  Non-zero values protect against thebuffer pool being filled by data that is referenced only for a brief period, such as during afull 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 oldsublist 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.

  This variable is often used in combination withinnodb_old_blocks_pct. For more information, seeSection 17.8.3.3, “Making the Buffer Pool Scan Resistant”. For information about buffer pool management, theLRU algorithm, andeviction policies, seeSection 17.5.1, “Buffer Pool”.

• innodb_online_alter_log_max_size

  Command-Line Format	--innodb-online-alter-log-max-size=#
  System Variable	innodb_online_alter_log_max_size
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	134217728
  Minimum Value	65536
  Maximum Value	2**64-1
  Unit	bytes

  Specifies an upper limit in bytes on the size of the temporary log files used duringonline DDL operations forInnoDB tables. 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 TABLE operation 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.

• innodb_open_files

  Command-Line Format	--innodb-open-files=#
  System Variable	innodb_open_files
  Scope	Global
  Dynamic (≥ 8.0.28)	Yes
  Dynamic (≤ 8.0.27)	No
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	-1 (signifies autosizing; do not assign this literal value)
  Minimum Value	10
  Maximum Value	2147483647

  Specifies the maximum number of files thatInnoDB can have open at one time. The minimum value is 10. Ifinnodb_file_per_table is disabled, the default value is 300; otherwise, the default value is 300 or thetable_open_cache setting, whichever is higher.

  As of MySQL 8.0.28, theinnodb_open_files limit can be set at runtime using aSELECT innodb_set_open_files_limit(N) statement, whereN is the desiredinnodb_open_files limit; for example:

  mysql> SELECT innodb_set_open_files_limit(1000);

  The statement executes a stored procedure that sets the new limit. If the procedure is successful, it returns the value of the newly set limit; otherwise, a failure message is returned.

  It is not permitted to setinnodb_open_files using aSET statement. To setinnodb_open_files at runtime, use theSELECT innodb_set_open_files_limit(N) statement described above.

  Settinginnodb_open_files=default is not supported. Only integer values are permitted.

  As of MySQL 8.0.28, to prevent non-LRU manged files from consuming the entireinnodb_open_files limit, non-LRU managed files are limited to 90 percent of theinnodb_open_files limit, which reserves 10 percent of theinnodb_open_files limit for LRU managed files.

  Temporary tablespace files were not counted toward theinnodb_open_files limit from MySQL 8.0.24 to MySQL 8.0.27.

• innodb_optimize_fulltext_only

  Command-Line Format	--innodb-optimize-fulltext-only[={OFF|ON}]
  System Variable	innodb_optimize_fulltext_only
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  Changes the wayOPTIMIZE TABLE operates onInnoDB tables. Intended to be enabled temporarily, during maintenance operations forInnoDB tables withFULLTEXT indexes.

  By default,OPTIMIZE TABLE reorganizes data in theclustered index of the table. When this option is enabled,OPTIMIZE TABLE skips the reorganization of table data, and instead processes newly added, deleted, and updated token data forInnoDBFULLTEXT indexes. For more information, seeOptimizing InnoDB Full-Text Indexes.

• innodb_page_cleaners

  Command-Line Format	--innodb-page-cleaners=#
  System Variable	innodb_page_cleaners
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	4
  Minimum Value	1
  Maximum Value	64

  The number of page cleaner threads that flush dirty pages from buffer pool instances. Page cleaner threads perform flush list and LRU flushing. When there are multiple page cleaner threads, buffer pool flushing tasks for each buffer pool instance are dispatched to idle page cleaner threads. Theinnodb_page_cleaners default value is 4. If the number of page cleaner threads exceeds the number of buffer pool instances,innodb_page_cleaners is automatically set to the same value asinnodb_buffer_pool_instances.

  If your workload is write-IO bound when flushing dirty pages from buffer pool instances to data files, and if your system hardware has available capacity, increasing the number of page cleaner threads may help improve write-IO throughput.

  Multithreaded page cleaner support extends to shutdown and recovery phases.

  Thesetpriority() system call is used on Linux platforms where it is supported, and where themysqld execution user is authorized to givepage_cleaner threads priority over other MySQL andInnoDB threads to help page flushing keep pace with the current workload.setpriority() support is indicated by thisInnoDB startup message:

  [Note] InnoDB: If the mysqld execution user is authorized, page cleanerthread priority can be changed. See the man page of setpriority().

  For systems where server startup and shutdown is not managed by systemd,mysqld execution user authorization can be configured in/etc/security/limits.conf. For example, ifmysqld is run under themysql user, you can authorize themysql user by adding these lines to/etc/security/limits.conf:

  mysql              hard    nice       -20mysql              soft    nice       -20

  For systemd managed systems, the same can be achieved by specifyingLimitNICE=-20 in a localized systemd configuration file. For example, create a file namedoverride.conf in/etc/systemd/system/mysqld.service.d/override.conf and add this entry:

  [Service]LimitNICE=-20

  After creating or changingoverride.conf, reload the systemd configuration, then tell systemd to restart the MySQL service:

  systemctl daemon-reloadsystemctl restart mysqld  # RPM platformssystemctl restart mysql   # Debian platforms

  For more information about using a localized systemd configuration file, seeConfiguring systemd for MySQL.

  After authorizing themysqld execution user, use thecat command to verify the configuredNice limits for themysqld process:

  $> cat /proc/mysqld_pid/limits | grep niceMax nice priority         18446744073709551596 18446744073709551596

• innodb_page_size

  Command-Line Format	--innodb-page-size=#
  System Variable	innodb_page_size
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Enumeration
  Default Value	16384
  Valid Values	4096 8192 16384 32768 65536

  Specifies thepage size forInnoDBtablespaces. 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_size can 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. SeeSection 17.8.1, “InnoDB Startup Configuration”.

  For both 32KB and 64KB page sizes, the maximum row length is approximately 16000 bytes.ROW_FORMAT=COMPRESSED is not supported wheninnodb_page_size is set to 32KB or 64KB. Forinnodb_page_size=32KB, extent size is 2MB. Forinnodb_page_size=64KB, extent size is 4MB.innodb_log_buffer_size should be set to at least 16M (the default) when using 32KB or 64KB page sizes.

  The default 16KB page size or larger is appropriate for a wide range ofworkloads, particularly for queries involving table scans and DML operations involving bulk updates. Smaller page sizes might be more efficient forOLTP workloads involving many small writes, where contention can be an issue when single pages contain many rows. Smaller pages might also be efficient withSSD storage devices, which typically use small block sizes. Keeping theInnoDB page size close to the storage device block size minimizes the amount of unchanged data that is rewritten to disk.

  The minimum file size for the first system tablespace data file (ibdata1) differs depending on theinnodb_page_size value. See theinnodb_data_file_path option description for more information.

  A MySQL instance using a particularInnoDB page size cannot use data files or log files from an instance that uses a different page size.

  For general I/O tuning advice, seeSection 10.5.8, “Optimizing InnoDB Disk I/O”.

• innodb_parallel_read_threads

  Command-Line Format	--innodb-parallel-read-threads=#
  Introduced	8.0.14
  System Variable	innodb_parallel_read_threads
  Scope	Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	4
  Minimum Value	1
  Maximum Value	256

  Defines the number of threads that can be used for parallel clustered index reads. Parallel scanning of partitions is supported as of MySQL 8.0.17. Parallel read threads can improveCHECK TABLE performance.InnoDB reads the clustered index twice during aCHECK TABLE operation. The second read can be performed in parallel. This feature does not apply to secondary index scans. Theinnodb_parallel_read_threads session variable must be set to a value greater than 1 for parallel clustered index reads to occur. The actual number of threads used to perform a parallel clustered index read is determined by theinnodb_parallel_read_threads setting or the number of index subtrees to scan, whichever is smaller. The pages read into the buffer pool during the scan are kept at the tail of the buffer pool LRU list so that they can be discarded quickly when free buffer pool pages are required.

  As of MySQL 8.0.17, the maximum number of parallel read threads (256) is the total number of threads for all client connections. If the thread limit is reached, connections fall back to using a single thread.

• innodb_print_all_deadlocks

  Command-Line Format	--innodb-print-all-deadlocks[={OFF|ON}]
  System Variable	innodb_print_all_deadlocks
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  When this option is enabled, information about alldeadlocks inInnoDB user transactions is recorded in themysqlderror log. Otherwise, you see information about only the last deadlock, using theSHOW ENGINE INNODB STATUS command. An occasionalInnoDB deadlock is not necessarily an issue, becauseInnoDB detects 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 issueDML orSELECT ... FOR UPDATE statements for multiple tables, so that each transaction accesses the tables in the same order, thus avoiding the deadlock condition.

  For related information, seeSection 17.7.5, “Deadlocks in InnoDB”.

• innodb_print_ddl_logs

  Command-Line Format	--innodb-print-ddl-logs[={OFF|ON}]
  System Variable	innodb_print_ddl_logs
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  Enabling this option causes MySQL to write DDL logs tostderr. For more information, seeViewing DDL Logs.

• innodb_purge_batch_size

  Command-Line Format	--innodb-purge-batch-size=#
  System Variable	innodb_purge_batch_size
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	300
  Minimum Value	1
  Maximum Value	5000

  Defines the number of undo log pages that purge parses and processes in one batch from thehistory list. In a multithreaded purge configuration, the coordinator purge thread dividesinnodb_purge_batch_size byinnodb_purge_threads and assigns that number of pages to each purge thread. Theinnodb_purge_batch_size variable also defines the number of undo log pages that purge frees after every 128 iterations through the undo logs.

  Theinnodb_purge_batch_size option is intended for advanced performance tuning in combination with theinnodb_purge_threads setting. Most users need not changeinnodb_purge_batch_size from its default value.

  For related information, seeSection 17.8.9, “Purge Configuration”.

• innodb_purge_threads

  Command-Line Format	--innodb-purge-threads=#
  System Variable	innodb_purge_threads
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	4
  Minimum Value	1
  Maximum Value	32

  The number of background threads devoted to theInnoDBpurge operation. Increasing the value creates additional purge threads, which can improve efficiency on systems whereDML operations are performed on multiple tables.

  For related information, seeSection 17.8.9, “Purge Configuration”.

• innodb_purge_rseg_truncate_frequency

  Command-Line Format	--innodb-purge-rseg-truncate-frequency=#
  System Variable	innodb_purge_rseg_truncate_frequency
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	128
  Minimum Value	1
  Maximum Value	128

  Defines the frequency with which the purge system frees rollback segments in terms of the number of times that purge is invoked. An undo tablespace cannot be truncated until its rollback segments are freed. Normally, the purge system frees rollback segments once every 128 times that purge is invoked. The default value is 128. Reducing this value increases the frequency with which the purge thread frees rollback segments.

  innodb_purge_rseg_truncate_frequency is intended for use withinnodb_undo_log_truncate. For more information, seeTruncating Undo Tablespaces.

• innodb_random_read_ahead

  Command-Line Format	--innodb-random-read-ahead[={OFF|ON}]
  System Variable	innodb_random_read_ahead
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  Enables the randomread-ahead technique for optimizingInnoDB I/O.

  For details about performance considerations for different types of read-ahead requests, seeSection 17.8.3.4, “Configuring InnoDB Buffer Pool Prefetching (Read-Ahead)”. For general I/O tuning advice, seeSection 10.5.8, “Optimizing InnoDB Disk I/O”.

• innodb_read_ahead_threshold

  Command-Line Format	--innodb-read-ahead-threshold=#
  System Variable	innodb_read_ahead_threshold
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	56
  Minimum Value	0
  Maximum Value	64

  Controls the sensitivity of linearread-ahead thatInnoDB uses to prefetch pages into thebuffer pool. IfInnoDB reads at leastinnodb_read_ahead_threshold pages sequentially from anextent (64 pages), it initiates an asynchronous read for the entire following extent. The permissible range of values is 0 to 64. A value of 0 disables read-ahead. For the default of 56,InnoDB must 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 theinnodb_read_ahead_threshold setting.SHOW ENGINE INNODB STATUS output displays counter information from theInnodb_buffer_pool_read_ahead andInnodb_buffer_pool_read_ahead_evicted global status variables, which report the number of pages brought into thebuffer pool by read-ahead requests, and the number of such pagesevicted from the buffer pool without ever being accessed, respectively. The status variables report global values since the last server restart.

  SHOW ENGINE INNODB STATUS also 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 STATUS and are displayed in theBUFFER POOL AND MEMORY section of theSHOW ENGINE INNODB STATUS output.

  For more information, seeSection 17.8.3.4, “Configuring InnoDB Buffer Pool Prefetching (Read-Ahead)”. For general I/O tuning advice, seeSection 10.5.8, “Optimizing InnoDB Disk I/O”.

• innodb_read_io_threads

  Command-Line Format	--innodb-read-io-threads=#
  System Variable	innodb_read_io_threads
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	4
  Minimum Value	1
  Maximum Value	64

  The number of I/O threads for read operations inInnoDB. Its counterpart for write threads isinnodb_write_io_threads. For more information, seeSection 17.8.5, “Configuring the Number of Background InnoDB I/O Threads”. For general I/O tuning advice, seeSection 10.5.8, “Optimizing InnoDB Disk I/O”.

  Note

  On Linux systems, running multiple MySQL servers (typically more than 12) with default settings forinnodb_read_io_threads,innodb_write_io_threads, and the Linuxaio-max-nr setting can exceed system limits. Ideally, increase theaio-max-nr setting; as a workaround, you might reduce the settings for one or both of the MySQL variables.

• innodb_read_only

  Command-Line Format	--innodb-read-only[={OFF|ON}]
  System Variable	innodb_read_only
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  StartsInnoDB in 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, seeSection 17.8.2, “Configuring InnoDB for Read-Only Operation”.

  Previously, enabling theinnodb_read_only system variable prevented creating and dropping tables only for theInnoDB storage engine. As of MySQL 8.0, enablinginnodb_read_only prevents these operations for all storage engines. Table creation and drop operations for any storage engine modify data dictionary tables in themysql system database, but those tables use theInnoDB storage engine and cannot be modified wheninnodb_read_only is enabled. The same principle applies to other table operations that require modifying data dictionary tables. Examples:

  • If theinnodb_read_only system variable is enabled,ANALYZE TABLE may fail because it cannot update statistics tables in the data dictionary, which useInnoDB. ForANALYZE TABLE operations that update the key distribution, failure may occur even if the operation updates the table itself (for example, if it is aMyISAM table). To obtain the updated distribution statistics, setinformation_schema_stats_expiry=0.

  • ALTER TABLEtbl_name ENGINE=engine_name fails because it updates the storage engine designation, which is stored in the data dictionary.

  In addition, other tables in themysql system database use theInnoDB storage engine in MySQL 8.0. Making those tables read only results in restrictions on operations that modify them. Examples:

  • Account-management statements such asCREATE USER andGRANT fail because the grant tables useInnoDB.

  • TheINSTALL PLUGIN andUNINSTALL PLUGIN plugin-management statements fail because themysql.plugin system table usesInnoDB.

  • TheCREATE FUNCTION andDROP FUNCTION loadable function-management statements fail because themysql.func system table usesInnoDB.

• innodb_redo_log_archive_dirs

  Command-Line Format	--innodb-redo-log-archive-dirs
  Introduced	8.0.17
  System Variable	innodb_redo_log_archive_dirs
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	String
  Default Value	NULL

  Defines labeled directories where redo log archive files can be created. You can define multiple labeled directories in a semicolon-separated list. For example:

  innodb_redo_log_archive_dirs='label1:/backups1;label2:/backups2'

  A label can be any string of characters, with the exception of colons (:), which are not permitted. An empty label is also permitted, but the colon (:) is still required in this case.

  A path must be specified, and the directory must exist. The path can contain colons (':'), but semicolons (;) are not permitted.

• innodb_redo_log_capacity

  Command-Line Format	--innodb-redo-log-capacity=#
  Introduced	8.0.30
  System Variable	innodb_redo_log_capacity
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	104857600
  Minimum Value	8388608
  Maximum Value (≥ 8.0.34)	549755813888
  Maximum Value (≥ 8.0.30, ≤ 8.0.33)	137438953472
  Unit	bytes

  Defines the amount of disk space occupied by redo log files.

  innodb_redo_log_capacity supercedes theinnodb_log_files_in_group andinnodb_log_file_size variables, which are both ignored ifinnodb_redo_log_capacity is defined.

  Ifinnodb_redo_log_capacity is not defined, and if neitherinnodb_log_file_size orinnodb_log_files_in_group are defined, then the defaultinnodb_redo_log_capacity value is used.

  Ifinnodb_redo_log_capacity is not defined, and ifinnodb_log_file_size and/orinnodb_log_files_in_group is defined, then the InnoDB redo log capacity is calculated as(innodb_log_files_in_group * innodb_log_file_size). This calculation does not modify the unusedinnodb_redo_log_capacity setting's value.

  TheInnodb_redo_log_capacity_resized server status variable indicates the total redo log capacity for all redo log files.

  If the server is started with--innodb-dedicated-server, the value ofinnodb_redo_log_capacity is set automatically if it is not explicitly defined. For more information, seeSection 17.8.12, “Enabling Automatic InnoDB Configuration for a Dedicated MySQL Server”.

  For more information, seeSection 17.6.5, “Redo Log”.

• innodb_redo_log_encrypt

  Command-Line Format	--innodb-redo-log-encrypt[={OFF|ON}]
  System Variable	innodb_redo_log_encrypt
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  Controls encryption of redo log data for tables encrypted using theInnoDBdata-at-rest encryption feature. Encryption of redo log data is disabled by default. For more information, seeRedo Log Encryption.

• innodb_replication_delay

  Command-Line Format	--innodb-replication-delay=#
  System Variable	innodb_replication_delay
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	0
  Minimum Value	0
  Maximum Value	4294967295
  Unit	milliseconds

  The replication thread delay in milliseconds on a replica server ifinnodb_thread_concurrency is reached.

• innodb_rollback_on_timeout

  Command-Line Format	--innodb-rollback-on-timeout[={OFF|ON}]
  System Variable	innodb_rollback_on_timeout
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  InnoDBrolls back only the last statement on a transaction timeout by default. If--innodb-rollback-on-timeout is specified, a transaction timeout causesInnoDB to abort and roll back the entire transaction.

  For more information, seeSection 17.21.5, “InnoDB Error Handling”.

• innodb_rollback_segments

  Command-Line Format	--innodb-rollback-segments=#
  System Variable	innodb_rollback_segments
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	128
  Minimum Value	1
  Maximum Value	128

  innodb_rollback_segments defines the number ofrollback segments allocated to each undo tablespace and the global temporary tablespace for transactions that generate undo records. The number of transactions that each rollback segment supports depends on theInnoDB page size and the number of undo logs assigned to each transaction. For more information, seeSection 17.6.6, “Undo Logs”.

  For related information, seeSection 17.3, “InnoDB Multi-Versioning”. For information about undo tablespaces, seeSection 17.6.3.4, “Undo Tablespaces”.

• innodb_saved_page_number_debug

  Command-Line Format	--innodb-saved-page-number-debug=#
  System Variable	innodb_saved_page_number_debug
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	0
  Minimum Value	0
  Maximum Value	2**32-1

  Saves a page number. Setting theinnodb_fil_make_page_dirty_debug option dirties the page defined byinnodb_saved_page_number_debug. Theinnodb_saved_page_number_debug option is only available if debugging support is compiled in using theWITH_DEBUGCMake option.

• innodb_segment_reserve_factor

  Command-Line Format	--innodb-segment-reserve-factor=#
  Introduced	8.0.26
  System Variable	innodb_segment_reserve_factor
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Numeric
  Default Value	12.5
  Minimum Value	0.03
  Maximum Value	40

  Defines the percentage of tablespace file segment pages reserved as empty pages. The setting is applicable to file-per-table and general tablespaces. Theinnodb_segment_reserve_factor default setting is 12.5 percent, which is the same percentage of pages reserved in previous MySQL releases.

  For more information, seeConfiguring the Percentage of Reserved File Segment Pages.

• innodb_sort_buffer_size

  Command-Line Format	--innodb-sort-buffer-size=#
  System Variable	innodb_sort_buffer_size
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	1048576
  Minimum Value	65536
  Maximum Value	67108864
  Unit	bytes

  This variable defines:

  • The sort buffer size for online DDL operations that create or rebuild secondary indexes. However, as of MySQL 8.0.27, this responsibility is subsumed by theinnodb_ddl_buffer_size variable.

  • The amount by which the temporary log file is extended when recording concurrent DML during anonline DDL operation, and the size of the temporary log file read buffer and write buffer.

  For related information, seeSection 17.12.3, “Online DDL Space Requirements”.

• innodb_spin_wait_delay

  Command-Line Format	--innodb-spin-wait-delay=#
  System Variable	innodb_spin_wait_delay
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	6
  Minimum Value	0
  Maximum Value (64-bit platforms, ≤ 8.0.13)	2**64-1
  Maximum Value (32-bit platforms, ≤ 8.0.13)	2**32-1
  Maximum Value (≥ 8.0.14)	1000

  The maximum delay between polls for aspin 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.

  Can be used in combination with theinnodb_spin_wait_pause_multiplier variable for greater control over the duration of spin-lock polling delays.

  For more information, seeSection 17.8.8, “Configuring Spin Lock Polling”.

• innodb_spin_wait_pause_multiplier

  Command-Line Format	--innodb-spin-wait-pause-multiplier=#
  Introduced	8.0.16
  System Variable	innodb_spin_wait_pause_multiplier
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	50
  Minimum Value	0
  Maximum Value	100

  Defines a multiplier value used to determine the number of PAUSE instructions in spin-wait loops that occur when a thread waits to acquire a mutex or rw-lock.

  For more information, seeSection 17.8.8, “Configuring Spin Lock Polling”.

• innodb_stats_auto_recalc

  Command-Line Format	--innodb-stats-auto-recalc[={OFF|ON}]
  System Variable	innodb_stats_auto_recalc
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON

  CausesInnoDB to automatically recalculatepersistent 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_persistent option is enabled. Automatic statistics recalculation may also be configured by specifyingSTATS_AUTO_RECALC=1 in aCREATE TABLE orALTER TABLE statement. The amount of data sampled to produce the statistics is controlled by theinnodb_stats_persistent_sample_pages variable.

  For more information, seeSection 17.8.10.1, “Configuring Persistent Optimizer Statistics Parameters”.

• innodb_stats_include_delete_marked

  Command-Line Format	--innodb-stats-include-delete-marked[={OFF|ON}]
  System Variable	innodb_stats_include_delete_marked
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  By default,InnoDB reads uncommitted data when calculating statistics. In the case of an uncommitted transaction that deletes rows from a table,InnoDB excludes 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_marked can be enabled to ensure thatInnoDB includes delete-marked records when calculating persistent optimizer statistics.

  Wheninnodb_stats_include_delete_marked is enabled,ANALYZE TABLE considers delete-marked records when recalculating statistics.

  innodb_stats_include_delete_marked is a global setting that affects allInnoDB tables. It is only applicable to persistent optimizer statistics.

  For related information, seeSection 17.8.10.1, “Configuring Persistent Optimizer Statistics Parameters”.

• innodb_stats_method

  Command-Line Format	--innodb-stats-method=value
  System Variable	innodb_stats_method
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Enumeration
  Default Value	nulls_equal
  Valid Values	nulls_equal nulls_unequal nulls_ignored

  How the server treatsNULL values when collectingstatistics about the distribution of index values forInnoDB tables. Permitted values arenulls_equal,nulls_unequal, andnulls_ignored. Fornulls_equal, allNULL index values are considered equal and form a single value group with a size equal to the number ofNULL values. Fornulls_unequal,NULL values are considered unequal, and eachNULL forms a distinct value group of size 1. Fornulls_ignored,NULL values are ignored.

  The method used to generate table statistics influences how the optimizer chooses indexes for query execution, as described inSection 10.3.8, “InnoDB and MyISAM Index Statistics Collection”.

• innodb_stats_on_metadata

  Command-Line Format	--innodb-stats-on-metadata[={OFF|ON}]
  System Variable	innodb_stats_on_metadata
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  This option only applies when optimizerstatistics are configured to be non-persistent. Optimizer statistics are not persisted to disk wheninnodb_stats_persistent is disabled or when individual tables are created or altered withSTATS_PERSISTENT=0. For more information, seeSection 17.8.10.2, “Configuring Non-Persistent Optimizer Statistics Parameters”.

  Wheninnodb_stats_on_metadata is enabled,InnoDB updates non-persistentstatistics when metadata statements such asSHOW TABLE STATUS or when accessing the Information SchemaTABLES orSTATISTICS tables. (These updates are similar to what happens forANALYZE TABLE.) When disabled,InnoDB does 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 ofexecution plans for queries that involveInnoDB tables.

  To change the setting, issue the statementSET GLOBAL innodb_stats_on_metadata=mode, wheremode is eitherON orOFF (or1 or0). Changing the setting requires privileges sufficient to set global system variables (seeSection 7.1.9.1, “System Variable Privileges”) and immediately affects the operation of all connections.

• innodb_stats_persistent

  Command-Line Format	--innodb-stats-persistent[={OFF|ON}]
  System Variable	innodb_stats_persistent
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON

  Specifies whetherInnoDB index statistics are persisted to disk. Otherwise, statistics may be recalculated frequently which can lead to variations inquery execution plans. This setting is stored with each table when the table is created. You can setinnodb_stats_persistent at the global level before creating a table, or use theSTATS_PERSISTENT clause of theCREATE TABLE andALTER TABLE statements to override the system-wide setting and configure persistent statistics for individual tables.

  For more information, seeSection 17.8.10.1, “Configuring Persistent Optimizer Statistics Parameters”.

• innodb_stats_persistent_sample_pages

  Command-Line Format	--innodb-stats-persistent-sample-pages=#
  System Variable	innodb_stats_persistent_sample_pages
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	20
  Minimum Value	1
  Maximum Value	18446744073709551615

  The number of indexpages to sample when estimatingcardinality and otherstatistics for an indexed column, such as those calculated byANALYZE TABLE. Increasing the value improves the accuracy of index statistics, which can improve thequery execution plan, at the expense of increased I/O during the execution ofANALYZE TABLE for anInnoDB table. For more information, seeSection 17.8.10.1, “Configuring Persistent Optimizer Statistics Parameters”.

  Note

  Setting a high value forinnodb_stats_persistent_sample_pages could result in lengthyANALYZE TABLE execution time. To estimate the number of database pages accessed byANALYZE TABLE, seeSection 17.8.10.3, “Estimating ANALYZE TABLE Complexity for InnoDB Tables”.

  innodb_stats_persistent_sample_pages only applies wheninnodb_stats_persistent is enabled for a table; wheninnodb_stats_persistent is disabled,innodb_stats_transient_sample_pages applies instead.

• innodb_stats_transient_sample_pages

  Command-Line Format	--innodb-stats-transient-sample-pages=#
  System Variable	innodb_stats_transient_sample_pages
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	8
  Minimum Value	1
  Maximum Value	18446744073709551615

  The number of indexpages to sample when estimatingcardinality and otherstatistics for an indexed column, such as those calculated byANALYZE TABLE. The default value is 8. Increasing the value improves the accuracy of index statistics, which can improve thequery execution plan, at the expense of increased I/O when opening anInnoDB table or recalculating statistics. For more information, seeSection 17.8.10.2, “Configuring Non-Persistent Optimizer Statistics Parameters”.

  Note

  Setting a high value forinnodb_stats_transient_sample_pages could result in lengthyANALYZE TABLE execution time. To estimate the number of database pages accessed byANALYZE TABLE, seeSection 17.8.10.3, “Estimating ANALYZE TABLE Complexity for InnoDB Tables”.

  innodb_stats_transient_sample_pages only applies wheninnodb_stats_persistent is disabled for a table; wheninnodb_stats_persistent is enabled,innodb_stats_persistent_sample_pages applies instead. Takes the place ofinnodb_stats_sample_pages. For more information, seeSection 17.8.10.2, “Configuring Non-Persistent Optimizer Statistics Parameters”.

• innodb_status_output

  Command-Line Format	--innodb-status-output[={OFF|ON}]
  System Variable	innodb_status_output
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  Enables or disables periodic output for the standardInnoDB Monitor. Also used in combination withinnodb_status_output_locks to enable or disable periodic output for theInnoDB Lock Monitor. For more information, seeSection 17.17.2, “Enabling InnoDB Monitors”.

• innodb_status_output_locks

  Command-Line Format	--innodb-status-output-locks[={OFF|ON}]
  System Variable	innodb_status_output_locks
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  Enables or disables theInnoDB Lock Monitor. When enabled, theInnoDB Lock Monitor prints additional information about locks inSHOW ENGINE INNODB STATUS output and in periodic output printed to the MySQL error log. Periodic output for theInnoDB Lock Monitor is printed as part of the standardInnoDB Monitor output. The standardInnoDB Monitor must therefore be enabled for theInnoDB Lock Monitor to print data to the MySQL error log periodically. For more information, seeSection 17.17.2, “Enabling InnoDB Monitors”.

• innodb_strict_mode

  Command-Line Format	--innodb-strict-mode[={OFF|ON}]
  System Variable	innodb_strict_mode
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON

  Wheninnodb_strict_mode is enabled,InnoDB returns errors rather than warnings when checking for invalid or incompatible table options.

  It checks thatKEY_BLOCK_SIZE,ROW_FORMAT,DATA DIRECTORY,TEMPORARY, andTABLESPACE options are compatible with each other and other settings.

  innodb_strict_mode=ON also enables a row size check when creating or altering a table, to preventINSERT orUPDATE from failing due to the record being too large for the selected page size.

  You can enable or disableinnodb_strict_mode on the command line when startingmysqld, or in a MySQLconfiguration file. You can also enable or disableinnodb_strict_mode at runtime with the statementSET [GLOBAL|SESSION] innodb_strict_mode=mode, wheremode is eitherON orOFF. Changing theGLOBAL setting requires privileges sufficient to set global system variables (seeSection 7.1.9.1, “System Variable Privileges”) and affects the operation of all clients that subsequently connect. Any client can change theSESSION setting forinnodb_strict_mode, and the setting affects only that client.

  As of MySQL 8.0.26, setting the session value of this system variable is a restricted operation. The session user must have privileges sufficient to set restricted session variables. SeeSection 7.1.9.1, “System Variable Privileges”.

• innodb_sync_array_size

  Command-Line Format	--innodb-sync-array-size=#
  System Variable	innodb_sync_array_size
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	1
  Minimum Value	1
  Maximum Value	1024

  Defines 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.

• innodb_sync_spin_loops

  Command-Line Format	--innodb-sync-spin-loops=#
  System Variable	innodb_sync_spin_loops
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	30
  Minimum Value	0
  Maximum Value	4294967295

  The number of times a thread waits for anInnoDB mutex to be freed before the thread is suspended.

• innodb_sync_debug

  Command-Line Format	--innodb-sync-debug[={OFF|ON}]
  System Variable	innodb_sync_debug
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  Enables sync debug checking for theInnoDB storage engine. This option is only available if debugging support is compiled in using theWITH_DEBUGCMake option.

• innodb_table_locks

  Command-Line Format	--innodb-table-locks[={OFF|ON}]
  System Variable	innodb_table_locks
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON

  Ifautocommit = 0,InnoDB honorsLOCK TABLES; MySQL does not return fromLOCK TABLES ... WRITE until all other threads have released all their locks to the table. The default value ofinnodb_table_locks is 1, which means thatLOCK TABLES causes InnoDB to lock a table internally ifautocommit = 0.

  innodb_table_locks = 0 has no effect for tables locked explicitly withLOCK TABLES ... WRITE. It does have an effect for tables locked for read or write byLOCK TABLES ... WRITE implicitly (for example, through triggers) or byLOCK TABLES ... READ.

  For related information, seeSection 17.7, “InnoDB Locking and Transaction Model”.

• innodb_temp_data_file_path

  Command-Line Format	--innodb-temp-data-file-path=file_name
  System Variable	innodb_temp_data_file_path
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	String
  Default Value	ibtmp1:12M:autoextend

  Defines the relative path, name, size, and attributes of global temporary tablespace data files. The global temporary tablespace stores rollback segments for changes made to user-created temporary tables.

  If no value is specified forinnodb_temp_data_file_path, the default behavior is to create a single auto-extending data file namedibtmp1 in theinnodb_data_home_dir directory. The initial file size is slightly larger than 12MB.

  The syntax for a global temporary tablespace data file specification includes the file name, file size, andautoextend andmax attributes:

  file_name:file_size[:autoextend[:max:max_file_size]]

  The global temporary tablespace data file cannot have the same name as anotherInnoDB data file. Any inability or error creating the global temporary tablespace data file is treated as fatal and server startup is refused.

  File sizes are specified in KB, MB, or GB by appendingK,M orG to the size value. The sum of file sizes must be slightly larger than 12MB.

  The size limit of individual files is determined by the operating system. File size can be more than 4GB on operating systems that support large files. Use of raw disk partitions for global temporary tablespace data files is not supported.

  Theautoextend andmax attributes can be used only for the data file specified last in theinnodb_temp_data_file_path setting. For example:

  [mysqld]innodb_temp_data_file_path=ibtmp1:50M;ibtmp2:12M:autoextend:max:500M

  Theautoextend option causes the data file to automatically increase in size when it runs out of free space. Theautoextend increment is 64MB by default. To modify the increment, change theinnodb_autoextend_increment variable setting.

  The directory path for global temporary tablespace data files is formed by concatenating the paths defined byinnodb_data_home_dir andinnodb_temp_data_file_path.

  Before runningInnoDB in read-only mode, setinnodb_temp_data_file_path to a location outside of the data directory. The path must be relative to the data directory. For example:

  --innodb-temp-data-file-path=../../../tmp/ibtmp1:12M:autoextend

  For more information, seeGlobal Temporary Tablespace.

• innodb_temp_tablespaces_dir

  Command-Line Format	--innodb-temp-tablespaces-dir=dir_name
  Introduced	8.0.13
  System Variable	innodb_temp_tablespaces_dir
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Directory name
  Default Value	#innodb_temp

  Defines the location whereInnoDB creates a pool of session temporary tablespaces at startup. The default location is the#innodb_temp directory in the data directory. A fully qualified path or path relative to the data directory is permitted.

  As of MySQL 8.0.16, session temporary tablespaces always store user-created temporary tables and internal temporary tables created by the optimizer usingInnoDB. (Previously, the on-disk storage engine for internal temporary tables was determined by theinternal_tmp_disk_storage_engine system variable, which is no longer supported. SeeStorage Engine for On-Disk Internal Temporary Tables.)

  For more information, seeSession Temporary Tablespaces.

• innodb_thread_concurrency

  Command-Line Format	--innodb-thread-concurrency=#
  System Variable	innodb_thread_concurrency
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	0
  Minimum Value	0
  Maximum Value	1000

  Defines the maximum number of threads permitted inside ofInnoDB. A value of 0 (the default) is interpreted as infinite concurrency (no limit). This variable is intended for performance tuning on high concurrency systems.

  InnoDB tries to keep the number of threads insideInnoDB less than or equal to theinnodb_thread_concurrency limit. Threads waiting for locks are not counted in the number of concurrently executing threads.

  The correct setting depends on workload and computing environment. 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. Test a range of values to determine the setting that provides the best performance.innodb_thread_concurrency is a dynamic variable, which permits experimenting with different settings on a live test system. If a particular setting performs poorly, you can quickly setinnodb_thread_concurrency back 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 consistently small and does not affect performance, setinnodb_thread_concurrency=0 (no limit).

  • If your workload is consistently heavy or occasionally spikes, set aninnodb_thread_concurrency value and adjust it until you find the number of threads that provides the best performance. For example, suppose that your system typically has 40 to 50 users, but periodically the number increases to 60, 70, or more. Through testing, you find that performance remains largely stable with a limit of 80 concurrent users. In this case, setinnodb_thread_concurrency to 80.

  • If you do not wantInnoDB to use more than a certain number of virtual CPUs for user threads (20 virtual CPUs, for example), setinnodb_thread_concurrency to this number (or possibly lower, depending on performance testing). If your goal is to isolate MySQL from other applications, consider binding themysqld process exclusively to the virtual CPUs. Be aware, however, that exclusive binding can result in non-optimal hardware usage if themysqld process is not consistently busy. In this case, you can bind themysqld process to the virtual CPUs but allow other applications to use some or all of the virtual CPUs.

    Note

    From an operating system perspective, using a resource management solution to manage how CPU time is shared among applications may be preferable to binding themysqld process. For example, you could assign 90% of virtual CPU time to a given application while other critical processesare not running, and scale that value back to 40% when other critical processesare running.

  • In some cases, the optimalinnodb_thread_concurrency setting can be smaller than the number of virtual CPUs.

  • Aninnodb_thread_concurrency value that is too high can cause performance regression due to increased contention on system internals and resources.

  • Monitor and analyze your system regularly. Changes to workload, number of users, or computing environment may require that you adjust theinnodb_thread_concurrency setting.

  A value of 0 disables thequeries inside InnoDB andqueries in queue counters in theROW OPERATIONS section ofSHOW ENGINE INNODB STATUS output.

  For related information, seeSection 17.8.4, “Configuring Thread Concurrency for InnoDB”.

• innodb_thread_sleep_delay

  Command-Line Format	--innodb-thread-sleep-delay=#
  System Variable	innodb_thread_sleep_delay
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	10000
  Minimum Value	0
  Maximum Value	1000000
  Unit	microseconds

  How longInnoDB threads sleep before joining theInnoDB queue, in microseconds. The default value is 10000. A value of 0 disables sleep. You can setinnodb_adaptive_max_sleep_delay to the highest value you would allow forinnodb_thread_sleep_delay, andInnoDB automatically adjustsinnodb_thread_sleep_delay up 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, seeSection 17.8.4, “Configuring Thread Concurrency for InnoDB”.

• innodb_tmpdir

  Command-Line Format	--innodb-tmpdir=dir_name
  System Variable	innodb_tmpdir
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Directory name
  Default Value	NULL

  Used to define an alternate directory for temporary sort files created during onlineALTER TABLE operations that rebuild the table.

  OnlineALTER TABLE operations that rebuild the table also create anintermediate table file in the same directory as the original table. Theinnodb_tmpdir option 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 ($TMPDIR on Unix,%TEMP% on Windows, or the directory specified by the--tmpdir configuration option). If a directory is specified, existence of the directory and permissions are only checked wheninnodb_tmpdir is configured using aSET statement. 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 TABLE operation reports an error ifinnodb_tmpdir is set to an invalid directory.innodb_tmpdir overrides the MySQLtmpdir setting but only for onlineALTER TABLE operations.

  TheFILE privilege is required to configureinnodb_tmpdir.

  Theinnodb_tmpdir option was introduced to help avoid overflowing a temporary file directory located on atmpfs file system. Such overflows could occur as a result of large temporary sort files created during onlineALTER TABLE operations that rebuild the table.

  In replication environments, only consider replicating theinnodb_tmpdir setting if all servers have the same operating system environment. Otherwise, replicating theinnodb_tmpdir setting could result in a replication failure when running onlineALTER TABLE operations that rebuild the table. If server operating environments differ, it is recommended that you configureinnodb_tmpdir on each server individually.

  For more information, seeSection 17.12.3, “Online DDL Space Requirements”. For information about onlineALTER TABLE operations, seeSection 17.12, “InnoDB and Online DDL”.

• innodb_trx_purge_view_update_only_debug

  Command-Line Format	--innodb-trx-purge-view-update-only-debug[={OFF|ON}]
  System Variable	innodb_trx_purge_view_update_only_debug
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  Pauses 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 theWITH_DEBUGCMake option.

• innodb_trx_rseg_n_slots_debug

  Command-Line Format	--innodb-trx-rseg-n-slots-debug=#
  System Variable	innodb_trx_rseg_n_slots_debug
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	0
  Minimum Value	0
  Maximum Value	1024

  Sets a debug flag that limitsTRX_RSEG_N_SLOTS to a given value for thetrx_rsegf_undo_find_free function that looks for free slots for undo log segments. This option is only available if debugging support is compiled in using theWITH_DEBUGCMake option.

• innodb_undo_directory

  Command-Line Format	--innodb-undo-directory=dir_name
  System Variable	innodb_undo_directory
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Directory name

  The path whereInnoDB creates undo tablespaces. Typically used to place undo tablespaces on a different storage device.

  There is no default value (it is NULL). If theinnodb_undo_directory variable is undefined, undo tablespaces are created in the data directory.

  The default undo tablespaces (innodb_undo_001 andinnodb_undo_002) created when the MySQL instance is initialized always reside in the directory defined by theinnodb_undo_directory variable.

  Undo tablespaces created usingCREATE UNDO TABLESPACE syntax are created in the directory defined by theinnodb_undo_directory variable if a different path is not specified.

  For more information, seeSection 17.6.3.4, “Undo Tablespaces”.

• innodb_undo_log_encrypt

  Command-Line Format	--innodb-undo-log-encrypt[={OFF|ON}]
  System Variable	innodb_undo_log_encrypt
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  Controls encryption of undo log data for tables encrypted using theInnoDBdata-at-rest encryption feature. Only applies to undo logs that reside in separateundo tablespaces. SeeSection 17.6.3.4, “Undo Tablespaces”. Encryption is not supported for undo log data that resides in the system tablespace. For more information, seeUndo Log Encryption.

• innodb_undo_log_truncate

  Command-Line Format	--innodb-undo-log-truncate[={OFF|ON}]
  System Variable	innodb_undo_log_truncate
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON

  When enabled, undo tablespaces that exceed the threshold value defined byinnodb_max_undo_log_size are marked for truncation. Only undo tablespaces can be truncated. Truncating undo logs that reside in the system tablespace is not supported. For truncation to occur, there must be at least two undo tablespaces.

  Theinnodb_purge_rseg_truncate_frequency variable can be used to expedite truncation of undo tablespaces.

  For more information, seeTruncating Undo Tablespaces.

• innodb_undo_tablespaces

  Command-Line Format	--innodb-undo-tablespaces=#
  Deprecated	Yes
  System Variable	innodb_undo_tablespaces
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	2
  Minimum Value	2
  Maximum Value	127

  Defines the number ofundo tablespaces used byInnoDB. The default and minimum value is 2.

  Note

  Theinnodb_undo_tablespaces variable is deprecated and is no longer configurable as of MySQL 8.0.14. Expect it to be removed in a future release.

  For more information, seeSection 17.6.3.4, “Undo Tablespaces”.

• innodb_use_fdatasync

  Command-Line Format	--innodb-use-fdatasync[={OFF|ON}]
  Introduced	8.0.26
  System Variable	innodb_use_fdatasync
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  On platforms that supportfdatasync() system calls, enabling theinnodb_use_fdatasync variable permits usingfdatasync() instead offsync() system calls for operating system flushes. Anfdatasync() call does not flush changes to file metadata unless required for subsequent data retrieval, providing a potential performance benefit.

  A subset ofinnodb_flush_method settings such asfsync,O_DSYNC, andO_DIRECT usefsync() system calls. Theinnodb_use_fdatasync variable is applicable when using those settings.

• innodb_use_native_aio

  Command-Line Format	--innodb-use-native-aio[={OFF|ON}]
  System Variable	innodb_use_native_aio
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON

  Specifies whether to use theasynchronous I/O subsystem. This variable cannot be changed while the server is running. Normally, you do not need to configure this option, because it is enabled by default.

  This feature improves the scalability of heavily I/O-bound systems, which typically show many pending reads/writes inSHOW ENGINE INNODB STATUS output.

  Running with a large number ofInnoDB I/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 preventsInnoDB from starting, you can start the server withinnodb_use_native_aio=0. This option may also be disabled automatically during startup ifInnoDB detects a potential problem such as a combination oftmpdir location,tmpfs file system, and Linux kernel that does not support AIO ontmpfs.

  For more information, seeSection 17.8.6, “Using Asynchronous I/O on Linux”.

• innodb_validate_tablespace_paths

  Command-Line Format	--innodb-validate-tablespace-paths[={OFF|ON}]
  Introduced	8.0.21
  System Variable	innodb_validate_tablespace_paths
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON

  Controls tablespace file path validation. At startup,InnoDB validates the paths of known tablespace files against tablespace file paths stored in the data dictionary in case tablespace files have been moved to a different location. Theinnodb_validate_tablespace_paths variable permits disabling tablespace path validation. This feature is intended for environments where tablespaces files are not moved. Disabling path validation improves startup time on systems with a large number of tablespace files.

  Warning

  Starting the server with tablespace path validation disabled after moving tablespace files can lead to undefined behavior.

  For more information, seeSection 17.6.3.7, “Disabling Tablespace Path Validation”.

• innodb_version

  TheInnoDB version number. In MySQL 8.0, separate version numbering forInnoDB does not apply and this value is the same theversion number of the server.

• innodb_write_io_threads

  Command-Line Format	--innodb-write-io-threads=#
  System Variable	innodb_write_io_threads
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	4
  Minimum Value	1
  Maximum Value	64

  The number of I/O threads for write operations inInnoDB. The default value is 4. Its counterpart for read threads isinnodb_read_io_threads. For more information, seeSection 17.8.5, “Configuring the Number of Background InnoDB I/O Threads”. For general I/O tuning advice, seeSection 10.5.8, “Optimizing InnoDB Disk I/O”.

  Note

  On Linux systems, running multiple MySQL servers (typically more than 12) with default settings forinnodb_read_io_threads,innodb_write_io_threads, and the Linuxaio-max-nr setting can exceed system limits. Ideally, increase theaio-max-nr setting; as a workaround, you might reduce the settings for one or both of the MySQL variables.

  Also take into consideration the value ofsync_binlog, which controls synchronization of the binary log to disk.

  For general I/O tuning advice, seeSection 10.5.8, “Optimizing InnoDB Disk I/O”.