MySQL innodb parameters

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InnoDB Startup Options and System Variables

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14.15.1 Changes toInnoDB Startup Options and System Variables

This section describes the InnoDB-related command options and 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 disableInnoDB checksums, you can use --innodb_checksums or --skip-innodb_checksums on the command line, or innodb_checksums or skip-innodb_checksums in an option file.

• 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 (see Section 5.1.5.2, “Dynamic System Variables”).

• For information about GLOBAL and SESSION variable scope modifiers, refer to the SET statement documentation.

• Certain options control the locations and layout of the InnoDB data files. Section 14.6, “InnoDB Configuration” explains how to use these options.

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

• For more information on specifying options and system variables, see Section 4.2.3, “Specifying Program Options”.

Table 14.4 InnoDB Option/Variable Reference

NameCmd-LineOption fileSystem VarStatus VarVar ScopeDynamicforeign_key_checks  Yes BothYeshave_innodb  Yes GlobalNoignore-builtin-innodbYesYes  GlobalNo- Variable: ignore_builtin_innodb  Yes GlobalNoinnodbYesYes    innodb_adaptive_flushingYesYesYes GlobalYesinnodb_adaptive_hash_indexYesYesYes GlobalYesinnodb_additional_mem_pool_sizeYesYesYes GlobalNoinnodb_autoextend_incrementYesYesYes GlobalYesinnodb_autoinc_lock_modeYesYesYes GlobalNoInnodb_buffer_pool_bytes_data   YesGlobalNoInnodb_buffer_pool_bytes_dirty   YesGlobalNoinnodb_buffer_pool_instancesYesYesYes GlobalNoInnodb_buffer_pool_pages_data   YesGlobalNoInnodb_buffer_pool_pages_dirty   YesGlobalNoInnodb_buffer_pool_pages_flushed   YesGlobalNoInnodb_buffer_pool_pages_free   YesGlobalNoInnodb_buffer_pool_pages_latched   YesGlobalNoInnodb_buffer_pool_pages_misc   YesGlobalNoInnodb_buffer_pool_pages_total   YesGlobalNoInnodb_buffer_pool_read_ahead   YesGlobalNoInnodb_buffer_pool_read_ahead_evicted   YesGlobalNoInnodb_buffer_pool_read_requests   YesGlobalNoInnodb_buffer_pool_reads   YesGlobalNoinnodb_buffer_pool_sizeYesYesYes GlobalNoInnodb_buffer_pool_wait_free   YesGlobalNoInnodb_buffer_pool_write_requests   YesGlobalNoinnodb_change_bufferingYesYesYes GlobalYesinnodb_checksumsYesYesYes GlobalNoinnodb_commit_concurrencyYesYesYes GlobalYesinnodb_concurrency_ticketsYesYesYes GlobalYesinnodb_data_file_pathYesYesYes GlobalNoInnodb_data_fsyncs   YesGlobalNoinnodb_data_home_dirYesYesYes GlobalNoInnodb_data_pending_fsyncs   YesGlobalNoInnodb_data_pending_reads   YesGlobalNoInnodb_data_pending_writes   YesGlobalNoInnodb_data_read   YesGlobalNoInnodb_data_reads   YesGlobalNoInnodb_data_writes   YesGlobalNoInnodb_data_written   YesGlobalNoInnodb_dblwr_pages_written   YesGlobalNoInnodb_dblwr_writes   YesGlobalNoinnodb_doublewriteYesYesYes GlobalNoinnodb_fast_shutdownYesYesYes GlobalYesinnodb_file_formatYesYesYes GlobalYesinnodb_file_format_checkYesYesYes GlobalNoinnodb_file_format_maxYesYesYes GlobalYesinnodb_file_per_tableYesYesYes GlobalYesinnodb_flush_log_at_trx_commitYesYesYes GlobalYesinnodb_flush_methodYesYesYes GlobalNoinnodb_force_load_corruptedYesYesYes GlobalNoinnodb_force_recoveryYesYesYes GlobalNoInnodb_have_atomic_builtins   YesGlobalNoinnodb_io_capacityYesYesYes GlobalYesinnodb_large_prefixYesYesYes GlobalYesinnodb_lock_wait_timeoutYesYesYes BothYesinnodb_locks_unsafe_for_binlogYesYesYes GlobalNoinnodb_log_buffer_sizeYesYesYes GlobalNoinnodb_log_file_sizeYesYesYes GlobalNoinnodb_log_files_in_groupYesYesYes GlobalNoinnodb_log_group_home_dirYesYesYes GlobalNoInnodb_log_waits   YesGlobalNoInnodb_log_write_requests   YesGlobalNoInnodb_log_writes   YesGlobalNoinnodb_max_dirty_pages_pctYesYesYes GlobalYesinnodb_max_purge_lagYesYesYes GlobalYesinnodb_mirrored_log_groupsYesYesYes GlobalNoinnodb_old_blocks_pctYesYesYes GlobalYesinnodb_old_blocks_timeYesYesYes GlobalYesinnodb_open_filesYesYesYes GlobalNoInnodb_os_log_fsyncs   YesGlobalNoInnodb_os_log_pending_fsyncs   YesGlobalNoInnodb_os_log_pending_writes   YesGlobalNoInnodb_os_log_written   YesGlobalNoInnodb_page_size   YesGlobalNoInnodb_pages_created   YesGlobalNoInnodb_pages_read   YesGlobalNoInnodb_pages_written   YesGlobalNoinnodb_print_all_deadlocksYesYesYes GlobalYesinnodb_purge_batch_sizeYesYesYes GlobalYesinnodb_purge_threadsYesYesYes GlobalNoinnodb_random_read_aheadYesYesYes GlobalYesinnodb_read_ahead_thresholdYesYesYes GlobalYesinnodb_read_io_threadsYesYesYes GlobalNoinnodb_replication_delayYesYesYes GlobalYesinnodb_rollback_on_timeoutYesYesYes GlobalNoinnodb_rollback_segmentsYesYesYes GlobalYesInnodb_row_lock_current_waits   YesGlobalNoInnodb_row_lock_time   YesGlobalNoInnodb_row_lock_time_avg   YesGlobalNoInnodb_row_lock_time_max   YesGlobalNoInnodb_row_lock_waits   YesGlobalNoInnodb_rows_deleted   YesGlobalNoInnodb_rows_inserted   YesGlobalNoInnodb_rows_read   YesGlobalNoInnodb_rows_updated   YesGlobalNoinnodb_spin_wait_delayYesYesYes GlobalYesinnodb_stats_methodYesYesYes GlobalYesinnodb_stats_on_metadataYesYesYes GlobalYesinnodb_stats_sample_pagesYesYesYes GlobalYesinnodb-status-fileYesYes    innodb_strict_modeYesYesYes BothYesinnodb_support_xaYesYesYes BothYesinnodb_sync_spin_loopsYesYesYes GlobalYesinnodb_table_locksYesYesYes BothYesinnodb_thread_concurrencyYesYesYes GlobalYesinnodb_thread_sleep_delayYesYesYes GlobalYesInnodb_truncated_status_writes   YesGlobalNoinnodb_use_native_aioYesYesYes GlobalNoinnodb_use_sys_mallocYesYesYes GlobalNoinnodb_version  Yes GlobalNoinnodb_write_io_threadsYesYesYes GlobalNotimed_mutexesYesYesYes GlobalYesunique_checks  Yes BothYes

InnoDB Command Options

• --ignore-builtin-innodb

  Deprecated5.5.22Command-Line Format--ignore-builtin-innodbOption-File Formatignore-builtin-innodbSystem Variable Nameignore_builtin_innodbVariable ScopeGlobalDynamic VariableNo Permitted ValuesTypeboolean

  In MySQL 5.1, this option caused the server to behave as if the built-in InnoDB were not present, which enabled InnoDB Plugin to be used instead. In MySQL 5.5,InnoDB is the default storage engine andInnoDB Plugin is not used, so this option has no effect. As of MySQL 5.5.22, it is deprecated and its use results in a warning.

• --innodb[=value]

  Controls loading of the InnoDB storage engine, if the server was compiled withInnoDB support. This option has a tristate format, with possible values ofOFF,ON, or FORCE. See Section 5.1.8.1, “Installing and Uninstalling Plugins”.

  To disable InnoDB, use --innodb=OFF or --skip-innodb. In this case, because the default storage engine isInnoDB, the server will not start unless you also use--default-storage-engine to set the default to some other engine.

• --innodb-status-file

  Command-Line Format--innodb-status-fileOption-File Formatinnodb-status-file Permitted ValuesTypebooleanDefaultOFF

  Controls whether InnoDB creates a file named innodb_status.pid in the MySQL data directory. If enabled,InnoDB periodically writes the output ofSHOW ENGINE INNODB STATUS to this file.

  By default, the file is not created. To create it, start mysqld with the --innodb-status-file=1 option. The file is deleted during normal shutdown.

• --skip-innodb

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

InnoDB System Variables

• ignore_builtin_innodb

  Deprecated5.5.22Command-Line Format--ignore-builtin-innodbOption-File Formatignore-builtin-innodbSystem Variable Nameignore_builtin_innodbVariable ScopeGlobalDynamic VariableNo Permitted ValuesTypeboolean

  See the description of --ignore-builtin-innodb under “InnoDB Command Options” earlier in this section.

• innodb_adaptive_flushing

  Command-Line Format--innodb_adaptive_flushing=#Option-File Formatinnodb_adaptive_flushingSystem Variable Nameinnodb_adaptive_flushingVariable ScopeGlobalDynamic VariableYes Permitted ValuesTypebooleanDefaultON

  Specifies whether to dynamically adjust the rate of flushing dirty pages in the InnoDB buffer 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 14.16.2.2, “Configuring the Rate of InnoDB Buffer Pool Flushing” for more information. For general I/O tuning advice, seeSection 8.5.7, “Optimizing InnoDB Disk I/O”.

• innodb_adaptive_hash_index

  Command-Line Format--innodb_adaptive_hash_index=#Option-File Formatinnodb_adaptive_hash_indexSystem Variable Nameinnodb_adaptive_hash_indexVariable ScopeGlobalDynamic VariableYes Permitted ValuesTypebooleanDefaultON

  Whether the InnoDB adaptive 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 14.5.13.5, “Adaptive Hash Indexes” for details.

  This variable is enabled by default. As of MySQL 5.5, You can modify this parameter using theSET GLOBAL statement, without restarting the server. Changing the setting requires theSUPER privilege. 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_additional_mem_pool_size

  Command-Line Format--innodb_additional_mem_pool_size=#Option-File Formatinnodb_additional_mem_pool_sizeSystem Variable Nameinnodb_additional_mem_pool_sizeVariable ScopeGlobalDynamic VariableNo Permitted ValuesTypenumericDefault8388608Range2097152 .. 4294967295

  The size in bytes of a memory pool InnoDB uses to storedata dictionary information and other internal data structures. The more tables you have in your application, the more memory you need to allocate here. IfInnoDB runs out of memory in this pool, it starts to allocate memory from the operating system and writes warning messages to the MySQL error log. The default value is 8MB.

  This variable relates to the InnoDB internal memory allocator, which is unused ifinnodb_use_sys_malloc is enabled.

• innodb_autoextend_increment

  Command-Line Format--innodb_autoextend_increment=#Option-File Formatinnodb_autoextend_incrementSystem Variable Nameinnodb_autoextend_incrementVariable ScopeGlobalDynamic VariableYes Permitted ValuesTypenumericDefault64Range1 .. 1000

  The increment size (in MB) for extending the size of an auto-extending system tablespace file when it becomes full. The default value is 8. This variable does not affect the per-table tablespace files that are created if you useinnodb_file_per_table=1. Those files are auto-extending regardless of the value ofinnodb_autoextend_increment. 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=#Option-File Formatinnodb_autoinc_lock_modeSystem Variable Nameinnodb_autoinc_lock_modeVariable ScopeGlobalDynamic VariableNo Permitted ValuesTypenumericDefault1Valid Values012

  The lock mode to use for generating auto-increment values. The permissible values are 0, 1, or 2, for “traditional”, “consecutive”, or“interleaved” lock mode, respectively.Section 14.9.5, “AUTO_INCREMENT Handling in InnoDB”, describes the characteristics of these modes.

  This variable has a default of 1 (“consecutive” lock mode).

• innodb_buffer_pool_instances

  Introduced5.5.4Command-Line Format--innodb_buffer_pool_instances=#Option-File Formatinnodb_buffer_pool_instancesSystem Variable Nameinnodb_buffer_pool_instancesVariable ScopeGlobalDynamic VariableNo Permitted ValuesTypenumericDefault1Range1 .. 64

  The number of regions that the InnoDB buffer pool is divided into. For systems with buffer pools in the multi-gigabyte range, dividing the buffer pool into separate instances can improve concurrency, by reducing contention as different threads read and write to cached pages. Each page that is stored in or read from the buffer pool is assigned to one of the buffer pool instances randomly, using a hashing function. Each buffer pool manages its own free lists, flush lists, LRUs, and all other data structures connected to a buffer pool, and is protected by its own buffer pool mutex.

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

• innodb_buffer_pool_size

  Command-Line Format--innodb_buffer_pool_size=#Option-File Formatinnodb_buffer_pool_sizeSystem Variable Nameinnodb_buffer_pool_sizeVariable ScopeGlobalDynamic VariableNo Permitted ValuesPlatform Bit Size32TypenumericDefault134217728Range5242880 .. 2**32-1 Permitted ValuesPlatform Bit Size64TypenumericDefault134217728Range5242880 .. 2**64-1

  The size in bytes of the buffer pool, the memory area where InnoDB caches table and index data. The default value is 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.

  The larger you set this value, the less disk I/O is needed to access the same data in tables more than once. On a dedicated database server, you might set this to up to 80% of the machine physical memory size. Be prepared to scale back this value if these other issues occur:

  • Competition for physical memory might 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 size.

  • The address space 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 large installations, this initialization time might be significant. For example, on a modern Linux x86_64 server, initialization of a 10GB buffer pool takes approximately 6 seconds. See Section 8.9.1, “The InnoDB Buffer Pool”.

• innodb_change_buffering

  Command-Line Format--innodb_change_buffering=#Option-File Formatinnodb_change_bufferingSystem Variable Nameinnodb_change_bufferingVariable ScopeGlobalDynamic VariableYes Permitted Values (<= 5.5.3)TypeenumerationDefaultinsertsValid Valuesinsertsnone Permitted Values (>= 5.5.4)TypeenumerationDefaultallValid Valuesinsertsdeletespurgeschangesallnone

  Whether InnoDB performs change buffering, an optimization that delays write operations to secondary indexes so that the I/O operations can be performed sequentially. The permitted values areinserts (buffer insert operations), deletes (buffer delete operations; strictly speaking, the writes that mark index records for later deletion during a purge operation),changes (buffer insert and delete-marking operations),purges (buffer purge operations, the writes when deleted index entries are finally garbage-collected),all (buffer insert, delete-marking, and purge operations) andnone (do not buffer any operations). The default is all. For details, see Section 14.16.5, “Configuring InnoDB Change Buffering”.

• innodb_checksums

  Command-Line Format--innodb_checksumsOption-File Formatinnodb_checksumsSystem Variable Nameinnodb_checksumsVariable ScopeGlobalDynamic VariableNo Permitted ValuesTypebooleanDefaultON

  InnoDB can use checksum validation on all pages read from the disk to ensure extra fault tolerance against broken hardware or data files. This validation is enabled by default. However, under some rare circumstances (such as when running benchmarks) this extra safety feature is unneeded and can be disabled with--skip-innodb-checksums.

• innodb_commit_concurrency

  Command-Line Format--innodb_commit_concurrency=#Option-File Formatinnodb_commit_concurrencySystem Variable Nameinnodb_commit_concurrencyVariable ScopeGlobalDynamic VariableYes Permitted ValuesTypenumericDefault0Range0 .. 1000

  The number of threads that can commit at the same time. A value of 0 (the default) permits any number of transactions to commit simultaneously.

  The value of innodb_commit_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_concurrency_tickets

  Command-Line Format--innodb_concurrency_tickets=#Option-File Formatinnodb_concurrency_ticketsSystem Variable Nameinnodb_concurrency_ticketsVariable ScopeGlobalDynamic VariableYes Permitted ValuesTypenumericDefault500Range1 .. 4294967295

  Determines the number of threads that can enter InnoDB 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 “free tickets” equal to the value of innodb_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 500.

• innodb_data_file_path

  Command-Line Format--innodb_data_file_path=nameOption-File Formatinnodb_data_file_pathSystem Variable Nameinnodb_data_file_pathVariable ScopeGlobalDynamic VariableNo Permitted ValuesTypestringDefaultibdata1:10M:autoextend

  The paths to individual InnoDB data files and their sizes. The full directory path to each data file is formed by concatenatinginnodb_data_home_dir to each path specified here. The file sizes are specified KB, MB or GB (1024MB) by appendingK,M or G to the size value. If specifying data file size in kilobytes (KB), do so in multiples of 1024. Otherwise, KB values are rounded off to nearest megabyte (MB) boundary. The sum of the sizes of the files must be at least slightly larger than 10MB. If you do not specify innodb_data_file_path, the default behavior is to create a single auto-extending data file, slightly larger than 10MB, namedibdata1. The size limit of individual files is determined by your operating system. You can set the file size to more than 4GB on those operating systems that support big files. You can alsouse raw disk partitions as data files. For detailed information on configuringInnoDBtablespace files, see Section 14.6, “InnoDB Configuration”.

• innodb_data_home_dir

  Command-Line Format--innodb_data_home_dir=pathOption-File Formatinnodb_data_home_dirSystem Variable Nameinnodb_data_home_dirVariable ScopeGlobalDynamic VariableNo Permitted ValuesTypedirectory name

  The common part of the directory path for all InnoDBdata files in thesystem tablespace. This setting does not affect the location of file-per-table tablespaces when innodb_file_per_table is enabled. The default value is the MySQL data directory. If you specify the value as an empty string, you can use absolute file paths ininnodb_data_file_path.

• innodb_doublewrite

  Command-Line Format--innodb-doublewriteOption-File Formatinnodb_doublewriteSystem Variable Nameinnodb_doublewriteVariable ScopeGlobalDynamic VariableNo Permitted ValuesTypeboolean

  If this variable is enabled (the default), InnoDB stores all data twice, first to thedoublewrite buffer, and then to the actual data files. This variable can be turned off with --skip-innodb_doublewrite for benchmarks or cases when top performance is needed rather than concern for data integrity or possible failures.

• innodb_fast_shutdown

  Command-Line Format--innodb_fast_shutdown[=#]Option-File Formatinnodb_fast_shutdownSystem Variable Nameinnodb_fast_shutdownVariable ScopeGlobalDynamic VariableYes Permitted ValuesTypenumericDefault1Valid Values012

  The InnoDB shutdown mode. If the value is 0, InnoDB does a slow shutdown, a full purge and an insert 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.

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

• innodb_file_format

  Command-Line Format--innodb_file_format=#Option-File Formatinnodb_file_formatSystem Variable Nameinnodb_file_formatVariable ScopeGlobalDynamic VariableYes Permitted Values (<= 5.5.6)TypestringDefaultBarracudaValid ValuesAntelopeBarracuda Permitted Values (>= 5.5.7)TypestringDefaultAntelopeValid ValuesAntelopeBarracuda

  The file format to use for new InnoDB tables. Currently,Antelope andBarracuda are supported. This applies only for tables that have their owntablespace, so for it to have an effect, innodb_file_per_table must be enabled. The Barracuda file format is required for certain InnoDB features such as table compression.

  Be aware that ALTER TABLE operations that recreate InnoDB tables (ALTER OFFLINE) will use the currentinnodb_file_format setting (the conditions outlined above still apply).

• innodb_file_format_check

  Command-Line Format--innodb_file_format_check=#Option-File Formatinnodb_file_format_checkSystem Variable Nameinnodb_file_format_checkVariable ScopeGlobalDynamic VariableNo Permitted ValuesTypestringDefaultAntelope Permitted Values (>= 5.5.1)TypestringDefaultBarracuda Permitted Values (>= 5.5.5)TypebooleanDefaultON

  As of MySQL 5.5.5, this variable can be set to 1 or 0 at server startup to enable or disable whetherInnoDB checks thefile format tag in the system tablespace (for example, Antelope or Barracuda). If the tag is checked and is higher than that supported by the current version ofInnoDB, an error occurs andInnoDB does not start. If the tag is not higher,InnoDB sets the value ofinnodb_file_format_max to the file format tag.

  Before MySQL 5.5.5, this variable can be set to 1 or 0 at server startup to enable or disable whetherInnoDB checks the file format tag in the shared tablespace. If the tag is checked and is higher than that supported by the current version ofInnoDB, an error occurs and InnoDB does not start. If the tag is not higher,InnoDB sets the value ofinnodb_file_format_check to the file format tag, which is the value seen at runtime.

  Note

  Despite the default value sometimes being displayed as ON orOFF, always use the numeric values 1 or 0 to turn this option on or off in your configuration file or command line.

• innodb_file_format_max

  Introduced5.5.5Command-Line Format--innodb_file_format_max=#Option-File Formatinnodb_file_format_maxSystem Variable Nameinnodb_file_format_maxVariable ScopeGlobalDynamic VariableYes Permitted ValuesTypestringDefaultAntelopeValid ValuesAntelopeBarracuda

  At server startup, InnoDB sets the value of this variable to thefile format tag in the system tablespace (for example, Antelope or Barracuda). If the server creates or opens a table with a “higher” file format, it sets the value of innodb_file_format_max to that format.

  This variable was added in MySQL 5.5.5.

• innodb_file_per_table

  Command-Line Format--innodb_file_per_tableOption-File Formatinnodb_file_per_tableSystem Variable Nameinnodb_file_per_tableVariable ScopeGlobalDynamic VariableYes Permitted Values (<= 5.5.6)TypebooleanDefaultON Permitted Values (>= 5.5.7)TypebooleanDefaultOFF

  When innodb_file_per_table is disabled, InnoDB stores the data for all tables and indexes in the ibdata files that make up the system tablespace. This setting reduces the performance overhead of filesystem operations for operations such asDROP TABLE or TRUNCATE TABLE. It is most appropriate for a server environment where entire storage devices are devoted to MySQL data. Because the system tablespace never shrinks, and is shared across all databases in aninstance, avoid loading huge amounts of temporary data on a space-constrained system wheninnodb_file_per_table=OFF. Set up a separate instance in such cases, so that you can drop the entire instance to reclaim the space.

  When innodb_file_per_table is enabled, InnoDB stores data and indexes for each newly created table in a separate .ibd file, rather than in the system tablespace. The storage for theseInnoDB tables is reclaimed when the tables are dropped or truncated. This setting enables several otherInnoDB features, such as table compression. See Section 14.8.2, “InnoDB File-Per-Table Mode” for details about such features as well as advantages and disadvantages of using file-per-table tablespaces.

  Be aware that enabling innodb_file_per_table also means that an ALTER TABLE operation will move InnoDB table from the system tablespace to an individual .ibd file in cases where ALTER TABLE recreates the table (ALTER OFFLINE).

  In MySQL 5.5 and higher, the configuration parameter innodb_file_per_table is dynamic, and can be setON orOFF using SET GLOBAL. Previously, the only way to set this parameter was in the MySQLconfiguration file (my.cnf or my.ini), and changing it required shutting down and restarting the server.

  Dynamically changing the value of this parameter requires the SUPER privilege and immediately affects the operation of all connections.

• innodb_flush_log_at_trx_commit

  Command-Line Format--innodb_flush_log_at_trx_commit[=#]Option-File Formatinnodb_flush_log_at_trx_commitSystem Variable Nameinnodb_flush_log_at_trx_commitVariable ScopeGlobalDynamic VariableYes Permitted ValuesTypeenumerationDefault1Valid Values012

  Controls the balance between strict ACID compliance for commit operations, and higher performance that is possible when commit-related I/O operations are rearranged and done in batches. You can achieve better performance by changing the default value, but then you can lose up to one second worth oftransactions in a crash.

  • The default value of 1 is required for full ACID compliance. With this value, thelog buffer is written out to the log file at each transaction commit and the flush to disk operation is performed on the log file.

  • With a value of 0, any mysqld process crash can erase the last second of transactions. The log buffer is written out to the log file once per second and the flush to disk operation is performed on the log file, but nothing is done at a transaction commit.

  • With a value of 2, an operating system crash or a power outage can erase the last second of commit records. The log buffer is written out to the file at each commit, but the flush to disk operation is not performed on it. However, the flushing on the log file takes place once per second also when the value is 2. Note that the once-per-second flushing is not 100% guaranteed to happen every second, due to process scheduling issues.

  • InnoDB's crash recovery works regardless of the value. Transactions are either applied entirely or erased entirely.

  For the greatest possible durability and consistency in a replication setup usingInnoDB with transactions, useinnodb_flush_log_at_trx_commit=1 and sync_binlog=1 in your master servermy.cnf file.

  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. Then the durability of transactions is not guaranteed even with the setting 1, and in the worst case a power outage can even 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 using the Unix commandhdparm to disable the caching of disk writes in hardware caches, or use some other command specific to the hardware vendor.

• innodb_flush_method

  Command-Line Format--innodb_flush_method=nameOption-File Formatinnodb_flush_methodSystem Variable Nameinnodb_flush_methodVariable ScopeGlobalDynamic VariableNo Permitted ValuesType (Linux)stringDefaultfdatasyncValid ValuesfdatasyncO_DSYNCO_DIRECT Permitted ValuesType (HP-UX)stringDefaultfdatasyncValid ValuesfdatasyncO_DSYNCO_DIRECT Permitted ValuesType (Solaris)stringDefaultfdatasyncValid ValuesfdatasyncO_DSYNCO_DIRECT

  Controls the system calls used to flush data to the InnoDB data files and log files, which can influence I/O throughput. This variable is relevant only for Unix and Linux systems. On Windows systems, the flush method is alwaysasync_unbuffered and cannot be changed.

  By default, InnoDB uses the fsync() system call to flush both the data and log files. If innodb_flush_method option is set to O_DSYNC, InnoDB uses O_SYNC to open and flush the log files, andfsync() to flush the data files. IfO_DIRECT is specified (available on some GNU/Linux versions, FreeBSD, and Solaris),InnoDB usesO_DIRECT (ordirectio() on Solaris) to open the data files, and usesfsync() to flush both the data and log files. Note thatInnoDB usesfsync() instead offdatasync(), and it does not useO_DSYNC by default because there have been problems with it on many varieties of Unix.

  Depending on hardware configuration, setting innodb_flush_method toO_DIRECT can either have either a positive or negative effect on performance. Benchmark your particular configuration to decide which setting to use. The mix of read and write operations in your workload can also affect which setting performs better for you. 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's filesystem 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 the same type of hardware and workload that reflects your production environment. For general I/O tuning advice, seeSection 8.5.7, “Optimizing InnoDB Disk I/O”.

  Formerly, a value of fdatasync also specified the default behavior. This value was removed, due to confusion that a value offdatasync causedfsync() system calls rather thanfdatasync() for flushing. To obtain the default value now, do not set any value forinnodb_flush_method at startup.

• innodb_force_load_corrupted

  Introduced5.5.18Command-Line Format--innodb_force_load_corruptedOption-File Formatinnodb_force_load_corruptedSystem Variable Nameinnodb_force_load_corruptedVariable ScopeGlobalDynamic VariableNo Permitted ValuesTypebooleanDefaultOFF

  Lets InnoDB load tables at startup that are marked as corrupted. Use only during troubleshooting, to recover data that is otherwise inaccessible. When troubleshooting is complete, turn this setting back off and restart the server.

• innodb_force_recovery

  Command-Line Format--innodb_force_recovery=#Option-File Formatinnodb_force_recoverySystem Variable Nameinnodb_force_recoveryVariable ScopeGlobalDynamic VariableNo Permitted ValuesTypenumericDefault0Range0 .. 6

  The crash recovery mode, typically only changed in serious troubleshooting situations. Possible values are from 0 to 6. The meanings of these values are described inSection 14.21.2, “Starting InnoDB on a Corrupted Database”.

  Warning

  Only set this variable greater than 0 in an emergency situation, to dump your tables from a corrupt database. As a safety measure,InnoDB prevents any changes to its data when this variable is greater than 0. This restriction also prohibits some queries that useWHERE or ORDER BY clauses, because high values can prevent queries from using indexes, to guard against possible corrupt index data.

• innodb_io_capacity

  Command-Line Format--innodb_io_capacity=#Option-File Formatinnodb_io_capacitySystem Variable Nameinnodb_io_capacityVariable ScopeGlobalDynamic VariableYes Permitted ValuesPlatform Bit Size32TypenumericDefault200Range100 .. 2**32-1 Permitted ValuesPlatform Bit Size64TypenumericDefault200Range100 .. 2**64-1

  The innodb_io_capacity parameter sets an upper limit on the I/O activity performed by theInnoDB background tasks, such asflushing pages from the buffer pool and merging data from the insert buffer. The default value is 200. For busy systems capable of higher I/O rates, you can set a higher value at server startup, to help the server handle the background maintenance work associated with a high rate of row changes. For systems with individual 5400 RPM or 7200 RPM drives, you might lower the value to the former default of 100.

  The innodb_io_capacity limit is a total limit for all buffer pool instances. When dirty pages are flushed, theinnodb_io_capacity limit is divided equally among buffer pool instances.

  This parameter should be set to approximately the number of I/O operations that the system can perform per second. Ideally, keep this setting as low as practical, but not so low that these background activities fall behind. If the value is too high, data is removed from the buffer pool and insert buffer too quickly to provide significant benefit from the caching.

  The value represents an estimated proportion of the I/O operations per second (IOPS) available to older-generation disk drives that could perform about 100 IOPS. The current default of 200 reflects that modern storage devices are capable of much higher I/O rates.

  In general, you can increase the value as a function of the number of drives used forInnoDB I/O, particularly fast drives capable of high numbers of IOPS. For example, systems that use multiple disks or solid-state disks forInnoDB are likely to benefit from the ability to control this parameter.

  Although you can specify a very high number, in practice such large values have little if any benefit; for example, a value of one million would be considered very high.

  You can set the innodb_io_capacity value to any number 100 or greater, and the default value is200. You can set the value of this parameter in the MySQL option file (my.cnf ormy.ini) or change it dynamically with the SET GLOBAL command, which requires the SUPER privilege.

  See Section 14.16.9, “Configuring the InnoDB Master Thread I/O Rate” for more guidelines about this option. For general information about InnoDB I/O performance, seeSection 8.5.7, “Optimizing InnoDB Disk I/O”.

• innodb_large_prefix

  Introduced5.5.14Command-Line Format--innodb_large_prefixOption-File Formatinnodb_large_prefixSystem Variable Nameinnodb_large_prefixVariable ScopeGlobalDynamic VariableYes Permitted ValuesTypebooleanDefaultOFF

  Enable this option to allow index key prefixes longer than 767 bytes (up to 3072 bytes), forInnoDB tables that use theDYNAMIC andCOMPRESSED row formats. (Creating such tables also requires the option valuesinnodb_file_format=barracuda and innodb_file_per_table=true.) See Section 14.9.7, “Limits on InnoDB Tables” for the relevant maximums associated with index key prefixes under various settings.

  For tables using the REDUNDANT andCOMPACT row formats, this option does not affect the allowed key prefix length. It does introduce a new error possibility. When this setting is enabled, attempting to create an index prefix with a key length greater than 3072 for aREDUNDANT or COMPACT table causes anER_INDEX_COLUMN_TOO_LONG error.

• innodb_lock_wait_timeout

  Command-Line Format--innodb_lock_wait_timeout=#Option-File Formatinnodb_lock_wait_timeoutSystem Variable Nameinnodb_lock_wait_timeoutVariable ScopeGlobal, SessionDynamic VariableYes Permitted ValuesTypenumericDefault50Range1 .. 1073741824

  The length of time in seconds an InnoDB transaction waits for a row lock before giving up. The default value is 50 seconds. A transaction that tries to access a row that is locked by 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 is rolled back (not the entire transaction). To have the entire transaction roll back, start the server with the--innodb_rollback_on_timeout option. See also Section 14.21.4, “InnoDB Error Handling”.

  You might decrease this value for highly interactive applications or OLTP systems, to display user feedback quickly or put the update into a queue for processing later. You might increase this value for long-running back-end operations, such as a transform step in a data warehouse that waits for other large insert or update operations to finish.

  innodb_lock_wait_timeout applies to InnoDB row locks only. A MySQL table lock does not happen inside InnoDB and this timeout does not apply to waits for table locks.

  The lock wait timeout value does not apply to deadlocks, because InnoDB detects them immediately and rolls back one of the deadlocked transactions.

  As of MySQL 5.5, innodb_lock_wait_timeout can be set at runtime with theSET GLOBAL orSET SESSION statement. Changing theGLOBAL setting requires theSUPER privilege 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_locks_unsafe_for_binlog

  Command-Line Format--innodb_locks_unsafe_for_binlogOption-File Formatinnodb_locks_unsafe_for_binlogSystem Variable Nameinnodb_locks_unsafe_for_binlogVariable ScopeGlobalDynamic VariableNo Permitted ValuesTypebooleanDefaultOFF

  This variable affects how InnoDB uses gap locking for searches and index scans. Normally,InnoDB uses an algorithm callednext-key locking that combines index-row locking with gap locking.InnoDB performs row-level locking in such a way that when it searches or scans a table index, it sets shared or exclusive locks on the index records it encounters. Thus, the row-level locks are actually index-record locks. In addition, a next-key lock on an index record also affects the “gap” before that index record. That is, a next-key lock is an index-record lock plus a gap lock on the gap preceding the index record. If one session has a shared or exclusive lock on record R in an index, another session cannot insert a new index record in the gap immediately beforeR in the index order. SeeSection 14.5.6, “InnoDB Record, Gap, and Next-Key Locks”.

  By default, the value of innodb_locks_unsafe_for_binlog is 0 (disabled), which means that gap locking is enabled:InnoDB uses next-key locks for searches and index scans. To enable the variable, set it to 1. This causes gap locking to be disabled:InnoDB uses only index-record locks for searches and index scans.

  Enabling innodb_locks_unsafe_for_binlog does not disable the use of gap locking for foreign-key constraint checking or duplicate-key checking.

  The effect of enabling innodb_locks_unsafe_for_binlog is similar to but not identical to setting the transaction isolation level toREAD COMMITTED:

  • Enabling innodb_locks_unsafe_for_binlog is a global setting and affects all sessions, whereas the isolation level can be set globally for all sessions, or individually per session.

  • innodb_locks_unsafe_for_binlog can be set only at server startup, whereas the isolation level can be set at startup or changed at runtime.

  READ COMMITTED therefore offers finer and more flexible control thaninnodb_locks_unsafe_for_binlog. For additional details about the effect of isolation level on gap locking, seeSection 13.3.6, “SET TRANSACTION Syntax”.

  Enabling innodb_locks_unsafe_for_binlog may cause phantom problems because other sessions can insert new rows into the gaps when gap locking is disabled. Suppose that there is an index on theid column of the child table and that you want to read and lock all rows from the table having an identifier value larger than 100, with the intention of updating some column in the selected rows later:

  SELECT * FROM child WHERE id > 100 FOR UPDATE;

  The query scans the index starting from the first record where id is greater than 100. If the locks set on the index records in that range do not lock out inserts made in the gaps, another session can insert a new row into the table. Consequently, if you were to execute the sameSELECT again within the same transaction, you would see a new row in the result set returned by the query. This also means that if new items are added to the database,InnoDB does not guarantee serializability. Therefore, ifinnodb_locks_unsafe_for_binlog is enabled, InnoDB guarantees at most an isolation level ofREAD COMMITTED. (Conflict serializability is still guaranteed.) For additional information about phantoms, seeSection 14.5.7, “Avoiding the Phantom Problem Using Next-Key Locking”.

  Enabling innodb_locks_unsafe_for_binlog has additional effects:

  • For UPDATE or DELETE statements, InnoDB holds locks only for rows that it updates or deletes. Record locks for nonmatching rows are released after MySQL has evaluated theWHERE condition. This greatly reduces the probability of deadlocks, but they can still happen.

  • For UPDATE statements, if a row is already locked, InnoDB performs a “semi-consistent” read, returning the latest committed version to MySQL so that MySQL can determine whether the row matches theWHERE condition of theUPDATE. If the row matches (must be updated), MySQL reads the row again and this timeInnoDB either locks it or waits for a lock on it.

  Consider the following example, beginning with this table:

  CREATE TABLE t (a INT NOT NULL, b INT) ENGINE = InnoDB;INSERT INTO t VALUES (1,2),(2,3),(3,2),(4,3),(5,2);COMMIT;

  In this case, table has no indexes, so searches and index scans use the hidden clustered index for record locking (seeSection 14.5.13.2, “Clustered and Secondary Indexes”).

  Suppose that one client performs an UPDATE using these statements:

  SET autocommit = 0;UPDATE t SET b = 5 WHERE b = 3;

  Suppose also that a second client performs an UPDATE by executing these statements following those of the first client:

  SET autocommit = 0;UPDATE t SET b = 4 WHERE b = 2;

  As InnoDB executes each UPDATE, it first acquires an exclusive lock for each row, and then determines whether to modify it. IfInnoDB does not modify the row and innodb_locks_unsafe_for_binlog is enabled, it releases the lock. Otherwise,InnoDB retains the lock until the end of the transaction. This affects transaction processing as follows.

  If innodb_locks_unsafe_for_binlog is disabled, the firstUPDATE acquires x-locks and does not release any of them:

  x-lock(1,2); retain x-lockx-lock(2,3); update(2,3) to (2,5); retain x-lockx-lock(3,2); retain x-lockx-lock(4,3); update(4,3) to (4,5); retain x-lockx-lock(5,2); retain x-lock

  The second UPDATE blocks as soon as it tries to acquire any locks (because first update has retained locks on all rows), and does not proceed until the firstUPDATE commits or rolls back:

  x-lock(1,2); block and wait for first UPDATE to commit or roll back

  If innodb_locks_unsafe_for_binlog is enabled, the firstUPDATE acquires x-locks and releases those for rows that it does not modify:

  x-lock(1,2); unlock(1,2)x-lock(2,3); update(2,3) to (2,5); retain x-lockx-lock(3,2); unlock(3,2)x-lock(4,3); update(4,3) to (4,5); retain x-lockx-lock(5,2); unlock(5,2)

  For the second UPDATE, InnoDB does a“semi-consistent” read, returning the latest committed version of each row to MySQL so that MySQL can determine whether the row matches theWHERE condition of the UPDATE:

  x-lock(1,2); update(1,2) to (1,4); retain x-lockx-lock(2,3); unlock(2,3)x-lock(3,2); update(3,2) to (3,4); retain x-lockx-lock(4,3); unlock(4,3)x-lock(5,2); update(5,2) to (5,4); retain x-lock

• innodb_log_buffer_size

  Command-Line Format--innodb_log_buffer_size=#Option-File Formatinnodb_log_buffer_sizeSystem Variable Nameinnodb_log_buffer_sizeVariable ScopeGlobalDynamic VariableNo Permitted ValuesTypenumericDefault8388608Range262144 .. 4294967295

  The size in bytes of the buffer that InnoDB uses to write to thelog files on disk. The default value is 8MB. A large log buffer enables large transactions to run without a 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 general I/O tuning advice, seeSection 8.5.7, “Optimizing InnoDB Disk I/O”.

• innodb_log_file_size

  Command-Line Format--innodb_log_file_size=#Option-File Formatinnodb_log_file_sizeSystem Variable Nameinnodb_log_file_sizeVariable ScopeGlobalDynamic VariableNo Permitted ValuesTypenumericDefault5242880Range1048576 .. 4GB / innodb_log_files_in_group

  The size in bytes of each log file in a log group. The combined size of log files (innodb_log_file_size *innodb_log_files_in_group) cannot exceed a maximum value that is slightly less than 4GB. A pair of 2047 MB log files, for example, would allow you to approach the range limit but not exceed it. The default value is 5MB. Sensible values range from 1MB to 1/N-th of the size of the buffer pool, whereN is the number of log files in the group. The larger the value, the less checkpoint flush activity is needed in the buffer pool, saving disk I/O. Larger log files also makecrash recovery slower, although improvements to recovery performance in MySQL 5.5 and higher make the log file size less of a consideration. For general I/O tuning advice, seeSection 8.5.7, “Optimizing InnoDB Disk I/O”.

• innodb_log_files_in_group

  Command-Line Format--innodb_log_files_in_group=#Option-File Formatinnodb_log_files_in_groupSystem Variable Nameinnodb_log_files_in_groupVariable ScopeGlobalDynamic VariableNo Permitted ValuesTypenumericDefault2Range2 .. 100

  The number of log files in the log group. InnoDB writes to the files in a circular fashion. The default (and recommended) value is 2. The location of these files is specified byinnodb_log_group_home_dir.

• innodb_log_group_home_dir

  Command-Line Format--innodb_log_group_home_dir=pathOption-File Formatinnodb_log_group_home_dirSystem Variable Nameinnodb_log_group_home_dirVariable ScopeGlobalDynamic VariableNo Permitted ValuesTypedirectory name

  The directory path to the InnoDB redo log files, whose number is specified by innodb_log_files_in_group. If you do not specify anyInnoDB log variables, the default is to create two files namedib_logfile0 andib_logfile1 in the MySQL data directory. Their size is given by the size of theinnodb_log_file_size system variable.

• innodb_max_dirty_pages_pct

  Command-Line Format--innodb_max_dirty_pages_pct=#Option-File Formatinnodb_max_dirty_pages_pctSystem Variable Nameinnodb_max_dirty_pages_pctVariable ScopeGlobalDynamic VariableYes Permitted ValuesTypenumericDefault75Range0 .. 99

  InnoDB tries to flush data from the buffer pool so that the percentage of dirty pages does not exceed this value. Specify an integer in the range from 0 to 99. The default value is 75.

  For additional information about this variable, see Section 14.16.2.2, “Configuring the Rate of InnoDB Buffer Pool Flushing”. For general I/O tuning advice, seeSection 8.5.7, “Optimizing InnoDB Disk I/O”.

• innodb_max_purge_lag

  Command-Line Format--innodb_max_purge_lag=#Option-File Formatinnodb_max_purge_lagSystem Variable Nameinnodb_max_purge_lagVariable ScopeGlobalDynamic VariableYes Permitted ValuesTypenumericDefault0Range0 .. 4294967295

  This variable controls how to delay INSERT, UPDATE, and DELETE operations when purge operations are lagging (see Section 14.5.12, “InnoDB Multi-Versioning”). The default value is 0 (no delays).

  The InnoDB transaction system maintains a list of transactions that have index records delete-marked byUPDATE or DELETE operations. The length of this list represents thepurge_lag value. Whenpurge_lag exceedsinnodb_max_purge_lag, eachINSERT, UPDATE, and DELETE operation is delayed by ((purge_lag/innodb_max_purge_lag)×10)–5 milliseconds. The delay is computed in the beginning of a purge batch, every ten seconds. The operations are not delayed if purge cannot run because of an oldconsistent read view that could see the rows to be purged.

  A typical setting for a problematic workload might be 1 million, assuming that transactions are small, only 100 bytes in size, and it is permissible to have 100MB of unpurgedInnoDB table rows.

  The lag value is displayed as the history list length in the TRANSACTIONS section of InnoDB Monitor output. For example, if the output includes the following lines, the lag value is 20:

  ------------TRANSACTIONS------------Trx id counter 0 290328385Purge done for trx's n:o < 0 290315608 undo n:o < 0 17History list length 20

  For general I/O tuning advice, see Section 8.5.7, “Optimizing InnoDB Disk I/O”.

• innodb_mirrored_log_groups

  Has no effect.

• innodb_old_blocks_pct

  Command-Line Format--innodb_old_blocks_pct=#Option-File Formatinnodb_old_blocks_pctSystem Variable Nameinnodb_old_blocks_pctVariable ScopeGlobalDynamic VariableYes Permitted ValuesTypenumericDefault37Range5 .. 95

  Specifies the approximate percentage of the InnoDBbuffer pool used for the old block sublist. The range of values is 5 to 95. The default value is 37 (that is, 3/8 of the pool). SeeSection 14.16.2.3, “Making the Buffer Pool Scan Resistant” for more information. SeeSection 8.9.1, “TheInnoDB Buffer Pool” for information about buffer pool management, such as theLRU algorithm and eviction policies.

• innodb_old_blocks_time

  Command-Line Format--innodb_old_blocks_time=#Option-File Formatinnodb_old_blocks_timeSystem Variable Nameinnodb_old_blocks_timeVariable ScopeGlobalDynamic VariableYes Permitted ValuesTypenumericDefault0Range0 .. 2**32-1

  Non-zero values protect against the buffer pool being filled up 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 (ms) a block inserted into the old sublist must stay there after its first access before it can be moved to the new sublist. If the value is 0, a block inserted into the old sublist moves immediately to the new sublist the first time it is accessed, no matter how soon after insertion the access occurs. If the value is greater than 0, blocks remain in the old sublist until an access occurs at least that many ms 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.

  This variable is often used in combination with innodb_old_blocks_pct. See Section 14.16.2.3, “Making the Buffer Pool Scan Resistant” for more information. SeeSection 8.9.1, “The InnoDB Buffer Pool” for information about buffer pool management, such as theLRU algorithm and eviction policies.

• innodb_open_files

  Command-Line Format--innodb_open_files=#Option-File Formatinnodb_open_filesSystem Variable Nameinnodb_open_filesVariable ScopeGlobalDynamic VariableNo Permitted ValuesTypenumericDefault300Range10 .. 4294967295

  This variable is relevant only if you use multiple InnoDBtablespaces. It specifies the maximum number of .ibd files that MySQL can keep open at one time. The minimum value is 10. The default value is 300.

  The file descriptors used for .ibd files are forInnoDB tables only. They are independent of those specified by the--open-files-limit server option, and do not affect the operation of the table cache.

• innodb_print_all_deadlocks

  Introduced5.5.30Command-Line Format--innodb_print_all_deadlocks=#Option-File Formatinnodb_print_all_deadlocksSystem Variable Nameinnodb_print_all_deadlocksVariable ScopeGlobalDynamic VariableYes Permitted ValuesTypebooleanDefaultOFF

  When this option is enabled, information about all deadlocks in InnoDB 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 happening 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 or SELECT ... FOR UPDATE statements for multiple tables, so that each transaction accesses the tables in the same order, thus avoiding the deadlock condition.

• innodb_purge_batch_size

  Introduced5.5.4Command-Line Format--innodb_purge_batch_size=#Option-File Formatinnodb_purge_batch_sizeSystem Variable Nameinnodb_purge_batch_sizeVariable ScopeGlobalDynamic VariableYes Permitted Values (>= 5.5.4)TypenumericDefault20Range1 .. 5000

  The granularity of changes, expressed in units of redo log records, that trigger a purge operation, flushing the changed buffer pool blocks to disk. This option is intended for tuning performance in combination with the settinginnodb_purge_threads=n, and typical users do not need to modify it.

• innodb_purge_threads

  Introduced5.5.4Command-Line Format--innodb_purge_threads=#Option-File Formatinnodb_purge_threadsSystem Variable Nameinnodb_purge_threadsVariable ScopeGlobalDynamic VariableNo Permitted Values (>= 5.5.4)TypenumericDefault0Range0 .. 1

  The number of background threads devoted to the InnoDB purge operation. Currently, can only be 0 (the default) or 1. The default value of 0 signifies that the purge operation is performed as part of themaster thread. Running the purge operation in its own thread can reduce internal contention within InnoDB, improving scalability. Currently, the performance gain might be minimal because the background thread might encounter different kinds of contention than before. This feature primarily lays the groundwork for future performance work.

• innodb_random_read_ahead

  Introduced5.5.16Command-Line Format--innodb_random_read_ahead=#Option-File Formatinnodb_random_read_aheadSystem Variable Nameinnodb_random_read_aheadVariable ScopeGlobalDynamic VariableYes Permitted ValuesTypebooleanDefaultOFF

  Enables the random read-ahead technique for optimizing InnoDB I/O. This is a setting that was originally on by default, then was removed in MySQL 5.5, and now is available but turned off by default. SeeSection 14.16.2.1, “Configuring InnoDB Buffer Pool Prefetching (Read-Ahead)” for details about the performance considerations for the different types of read-ahead requests. For general I/O tuning advice, seeSection 8.5.7, “Optimizing InnoDB Disk I/O”.

• innodb_read_ahead_threshold

  Command-Line Format--innodb_read_ahead_threshold=#Option-File Formatinnodb_read_ahead_thresholdSystem Variable Nameinnodb_read_ahead_thresholdVariable ScopeGlobalDynamic VariableYes Permitted ValuesTypenumericDefault56Range0 .. 64

  Controls the sensitivity of linear read-ahead that InnoDB uses to prefetch pages into thebuffer pool. IfInnoDB reads at least innodb_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. The default is 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 this read-ahead mechanism, and how many of them are evicted from the buffer pool without ever being accessed, can be useful to help fine-tune theinnodb_read_ahead_threshold parameter. As of MySQL 5.5,SHOW ENGINE INNODB STATUS output displays counter information from theInnodb_buffer_pool_read_ahead andInnodb_buffer_pool_read_ahead_evicted global status variables. These variables indicate the number of pages brought into thebuffer pool by read-ahead requests, and the number of such pages evicted from the buffer pool without ever being accessed respectively. These counters provide global values since the last server restart.

  SHOW ENGINE INNODB STATUS also shows the rate at which the read-ahead pages are read in 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 of SHOW ENGINE INNODB STATUS and are displayed in theBUFFER POOL AND MEMORY section of the output.

  See Section 14.16.2.1, “Configuring InnoDB Buffer Pool Prefetching (Read-Ahead)” for more information. For general I/O tuning advice, seeSection 8.5.7, “Optimizing InnoDB Disk I/O”.

• innodb_read_io_threads

  Command-Line Format--innodb_read_io_threads=#Option-File Formatinnodb_read_io_threadsSystem Variable Nameinnodb_read_io_threadsVariable ScopeGlobalDynamic VariableNo Permitted ValuesTypenumericDefault4Range1 .. 64

  The number of I/O threads for read operations in InnoDB. The default value is 4. Its counterpart for write threads isinnodb_write_io_threads. See Section 14.16.7, “Configuring the Number of Background InnoDB I/O Threads” for more information. For general I/O tuning advice, seeSection 8.5.7, “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 Linux aio-max-nr setting can exceed system limits. Ideally, increase the aio-max-nr setting; as a workaround, you might reduce the settings for one or both of the MySQL configuration options.

• innodb_replication_delay

  Command-Line Format--innodb_replication_delay=#Option-File Formatinnodb_replication_delaySystem Variable Nameinnodb_replication_delayVariable ScopeGlobalDynamic VariableYes Permitted ValuesTypenumericDefault0Range0 .. 4294967295

  The replication thread delay (in ms) on a slave server if innodb_thread_concurrency is reached.

• innodb_rollback_on_timeout

  Command-Line Format--innodb_rollback_on_timeoutOption-File Formatinnodb_rollback_on_timeoutSystem Variable Nameinnodb_rollback_on_timeoutVariable ScopeGlobalDynamic VariableNo Permitted ValuesTypebooleanDefaultOFF

  In MySQL 5.5, InnoDB rolls 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 (the same behavior as in MySQL 4.1).

• innodb_rollback_segments

  Introduced5.5.11Command-Line Format--innodb_rollback_segments=#Option-File Formatinnodb_rollback_segmentsSystem Variable Nameinnodb_rollback_segmentsVariable ScopeGlobalDynamic VariableYes Permitted ValuesTypenumericDefault128Range1 .. 128

  Defines how many of the rollback segments in the system tablespace that InnoDB uses within a transaction. You might reduce this value from its default of 128 if a smaller number of rollback segments performs better for your workload.

• innodb_spin_wait_delay

  Command-Line Format--innodb_spin_wait_delay=#Option-File Formatinnodb_spin_wait_delaySystem Variable Nameinnodb_spin_wait_delayVariable ScopeGlobalDynamic VariableYes Permitted ValuesTypenumericDefault6Range0 .. 4294967295

  The maximum delay between polls for a spin lock. The low-level implementation of this mechanism varies depending on the combination of hardware and operating system, so the delay does not correspond to a fixed time interval. The default value is 6. SeeSection 14.16.11, “Configuring Spin Lock Polling” for more information.

• innodb_stats_method

  Introduced5.5.10Command-Line Format--innodb_stats_method=nameOption-File Formatinnodb_stats_methodSystem Variable Nameinnodb_stats_methodVariable ScopeGlobalDynamic VariableYes Permitted ValuesTypeenumerationDefaultnulls_equalValid Valuesnulls_equalnulls_unequalnulls_ignored

  How the server treats NULL values when collectingstatistics about the distribution of index values for InnoDB tables. This variable has three possible values,nulls_equal,nulls_unequal, andnulls_ignored. Fornulls_equal, allNULL index values are considered equal and form a single value group that has 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. For nulls_ignored,NULL values are ignored.

  The method that is used for generating table statistics influences how the optimizer chooses indexes for query execution, as described inSection 8.3.7, “InnoDB and MyISAM Index Statistics Collection”.

• innodb_stats_on_metadata

  Introduced5.5.4Command-Line Format--innodb_stats_on_metadataOption-File Formatinnodb_stats_on_metadataSystem Variable Nameinnodb_stats_on_metadataVariable ScopeGlobalDynamic VariableYes Permitted ValuesTypebooleanDefaultON

  When this variable is enabled (which is the default, as before the variable was created),InnoDB updatesstatistics when metadata statements such as SHOW TABLE STATUS or SHOW INDEX are run, or when accessing the INFORMATION_SCHEMA tables TABLES or STATISTICS. (These updates are similar to what happens forANALYZE TABLE.) When disabled, InnoDB does not update statistics during these operations. Disabling this variable 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 statement SET GLOBAL innodb_stats_on_metadata=mode, wheremode is eitherON or OFF (or1 or 0). Changing this setting requires theSUPER privilege and immediately affects the operation of all connections.

• innodb_stats_sample_pages

  Command-Line Format--innodb_stats_sample_pages=#Option-File Formatinnodb_stats_sample_pagesSystem Variable Nameinnodb_stats_sample_pagesVariable ScopeGlobalDynamic VariableYes Permitted ValuesTypenumericDefault8Range1 .. 2**64-1

  The number of index pages to sample for index distribution statistics such as are calculated by ANALYZE TABLE. The default value is 8. For additional information, seeSection 14.16.15, “Configuring Optimizer Statistics Parameters”.

  Setting a high value for innodb_stats_sample_pages could result in lengthyANALYZE TABLE execution time. To estimate the number of database pages accessed byANALYZE TABLE, see Section 14.16.16, “Estimating ANALYZE TABLE Complexity forInnoDB Tables”.

• innodb_strict_mode

  Command-Line Format--innodb_strict_mode=#Option-File Formatinnodb_strict_modeSystem Variable Nameinnodb_strict_modeVariable ScopeGlobal, SessionDynamic VariableYes Permitted ValuesTypebooleanDefaultOFF

  When innodb_strict_mode is ON, InnoDB returns errors rather than warnings for certain conditions. The default value isOFF.

  Strict mode helps guard against ignored typos and syntax errors in SQL, or other unintended consequences of various combinations of operational modes and SQL statements. When innodb_strict_mode isON, InnoDB raises error conditions in certain cases, rather than issuing a warning and processing the specified statement (perhaps with unintended behavior). This is analogous tosql_mode in MySQL, which controls what SQL syntax MySQL accepts, and determines whether it silently ignores errors, or validates input syntax and data values.

  The innodb_strict_mode setting affects the handling of syntax errors forCREATE TABLE, ALTER TABLE and CREATE INDEX statements. innodb_strict_mode also enables a record size check, so that anINSERT orUPDATE never fails due to the record being too large for the selected page size.

  Oracle recommends enabling innodb_strict_mode when usingROW_FORMAT andKEY_BLOCK_SIZE clauses onCREATE TABLE,ALTER TABLE, and CREATE INDEX statements. When innodb_strict_mode is OFF, InnoDB ignores conflicting clauses and creates the table or index, with only a warning in the message log. The resulting table might have different behavior than you intended, such as having no compression when you tried to create a compressed table. When innodb_strict_mode is ON, such problems generate an immediate error and the table or index is not created, avoiding a troubleshooting session later.

  You can turn innodb_strict_mode ON or OFF on the command line when you start mysqld, or in the configuration file my.cnf or my.ini. You can also enable or disable innodb_strict_mode at runtime with the statementSET [GLOBAL|SESSION] innodb_strict_mode=mode, wheremode is eitherON orOFF. Changing theGLOBAL setting requires theSUPER privilege 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.

• innodb_support_xa

  Command-Line Format--innodb_support_xaOption-File Formatinnodb_support_xaSystem Variable Nameinnodb_support_xaVariable ScopeGlobal, SessionDynamic VariableYes Permitted ValuesTypebooleanDefaultTRUE

  Enables InnoDB support for two-phase commit in XA transactions, causing an extra disk flush for transaction preparation. This setting is the default. The XA mechanism is used internally and is essential for any server that has its binary log turned on and is accepting changes to its data from more than one thread. If you turn it off, transactions can be written to the binary log in a different order from the one in which the live database is committing them. This can produce different data when the binary log is replayed in disaster recovery or on a replication slave. Do not turn it off on a replication master server unless you have an unusual setup where only one thread is able to change data.

  For a server that is accepting data changes from only one thread, it is safe and recommended to turn off this option to improve performance forInnoDB tables. For example, you can turn it off on replication slaves where only the replication SQL thread is changing data.

  You can also turn off this option if you do not need it for safe binary logging or replication, and you also do not use an external XA transaction manager.

• innodb_sync_spin_loops

  Command-Line Format--innodb_sync_spin_loops=#Option-File Formatinnodb_sync_spin_loopsSystem Variable Nameinnodb_sync_spin_loopsVariable ScopeGlobalDynamic VariableYes Permitted ValuesTypenumericDefault30Range0 .. 4294967295

  The number of times a thread waits for an InnoDB mutex to be freed before the thread is suspended. The default value is 30.

• innodb_table_locks

  Command-Line Format--innodb_table_locksOption-File Formatinnodb_table_locksSystem Variable Nameinnodb_table_locksVariable ScopeGlobal, SessionDynamic VariableYes Permitted ValuesTypebooleanDefaultTRUE

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

  As of MySQL 5.5.3, innodb_table_locks = 0 has no effect for tables locked explicitly withLOCK TABLES ... WRITE. It still has an effect for tables locked for read or write byLOCK TABLES ... WRITE implicitly (for example, through triggers) or byLOCK TABLES ... READ.

• innodb_thread_concurrency

  Command-Line Format--innodb_thread_concurrency=#Option-File Formatinnodb_thread_concurrencySystem Variable Nameinnodb_thread_concurrencyVariable ScopeGlobalDynamic VariableYes Permitted ValuesTypenumericDefault0Range0 .. 1000

  InnoDB tries to keep the number of operating system threads concurrently insideInnoDB less than or equal to the limit given by this variable. Once the number of threads reaches this limit, additional threads are placed into a wait state within a FIFO queue for execution. Threads waiting for locks are not counted in the number of concurrently executing threads.

  The correct value for this variable is dependent on environment and workload. Try a range of different values to determine what value works for your applications. A recommended value is 2 times the number of CPUs plus the number of disks.

  The range of this variable is 0 to 1000. A value of 0 (the default) is interpreted as infinite concurrency (no concurrency checking). Disabling thread concurrency checking enables InnoDB to create as many threads as it needs. A value of 0 also disables thequeries inside InnoDB and queries in queue counters in theROW OPERATIONS section ofSHOW ENGINE INNODB STATUS output.

• innodb_thread_sleep_delay

  Command-Line Format--innodb_thread_sleep_delay=#Option-File Formatinnodb_thread_sleep_delaySystem Variable Nameinnodb_thread_sleep_delayVariable ScopeGlobalDynamic VariableYes Permitted Values (<= 5.5.36)Platform Bit Size32TypenumericDefault10000Range0 .. 4294967295 Permitted Values (<= 5.5.36)Platform Bit Size64TypenumericDefault10000Range0 .. 18446744073709551615 Permitted Values (>= 5.5.37)TypenumericDefault10000Range0 .. 1000000

  How long InnoDB threads sleep before joining the InnoDB queue, in microseconds. The default value is 10,000. A value of 0 disables sleep.

• innodb_use_native_aio

  Introduced5.5.4Command-Line Format--innodb_use_native_aio=#Option-File Formatinnodb_use_native_aioSystem Variable Nameinnodb_use_native_aioVariable ScopeGlobalDynamic VariableNo Permitted ValuesTypebooleanDefaultON

  Specifies whether to use the Linux asynchronous I/O subsystem. This variable applies to Linux systems only, and cannot be changed while the server is running. Normally, you do not need to touch this option, because it is enabled by default.

  As of MySQL 5.5, the asynchronous I/O capability that InnoDB has on Windows systems is available on Linux systems. (Other Unix-like systems continue to use synchronous I/O calls.) This feature improves the scalability of heavily I/O-bound systems, which typically show many pending reads/writes in the output of the command SHOW ENGINE INNODB STATUS\G.

  Running with a large number of InnoDB 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 prevents InnoDB from starting, you can start the server with innodb_use_native_aio=0 disabled (use innodb_use_native_aio=0 in the option file). This option may also be turned off automatically during startup ifInnoDB detects a potential problem such as a combination oftmpdir location, tmpfs filesystem, and Linux kernel that does not support AIO ontmpfs.

  This variable was added in MySQL 5.5.4.

• innodb_use_sys_malloc

  Command-Line Format--innodb_use_sys_malloc=#Option-File Formatinnodb_use_sys_mallocSystem Variable Nameinnodb_use_sys_mallocVariable ScopeGlobalDynamic VariableNo Permitted ValuesTypebooleanDefaultON

  Whether InnoDB uses the operating system memory allocator (ON) or its own (OFF). The default value isON. SeeSection 14.16.4, “Configuring the Memory Allocator for InnoDB” for more information.

• innodb_version

  The InnoDB version number. Starting in 5.5.30, the separate numbering forInnoDB is discontinued and this value is the same as for theversion variable.

• innodb_write_io_threads

  Command-Line Format--innodb_write_io_threads=#Option-File Formatinnodb_write_io_threadsSystem Variable Nameinnodb_write_io_threadsVariable ScopeGlobalDynamic VariableNo Permitted ValuesTypenumericDefault4Range1 .. 64

  The number of I/O threads for write operations in InnoDB. The default value is 4. Its counterpart for read threads isinnodb_read_io_threads. See Section 14.16.7, “Configuring the Number of Background InnoDB I/O Threads” for more information. For general I/O tuning advice, seeSection 8.5.7, “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 Linux aio-max-nr setting can exceed system limits. Ideally, increase the aio-max-nr setting; as a workaround, you might reduce the settings for one or both of the MySQL configuration options.

You should also take into consideration the value of sync_binlog, which controls synchronization of the binary log to disk.

For general I/O tuning advice, see Section 8.5.7, “Optimizing InnoDB Disk I/O”.

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User Comments

Posted by Morgan Tocker on December 28 2006 1:21am[Delete] [Edit]

Be careful when being too aggressive with settings like innodb_buffer_pool_size. Although your system might have a lot of RAM installed, a 32-bit Linux operating can't allocate more than 2.2-2.7G* per process.

* This limit varies in different kernels.

Posted by Sunny Walia on April 4 2007 1:55am[Delete] [Edit]

I am using innodb_file_per_table to separate the files out so when i delete database, we can get our disk usage back. I go into details in my blog which I hope helps somebody.
http://crazytoon.com/2007/04/03/mysql-ibdata-files-do-not-shrink-on-database-deletion-innodb/

Posted by Brian Aker on August 16 2007 3:08pm[Delete] [Edit]

Commentary on Innodb parameters for an 8way machine:
http://krow.livejournal.com/542306.html

Posted by Willem de Groot on September 20 2007 3:39pm[Delete] [Edit]

Changing innodb_log_file_size can yield strange errors, such as: Incorrect information in file: './db010840/notifications.frm'

This is particularly of importance when performing a file based sync to setup replication. If you have a different (or no) innodb_log_file_size setting at the slave, you will be puzzled for hours (I was).

Posted by Simon Mudd on October 13 2009 3:25pm[Delete] [Edit]

NOTE: The time to Initialise the innodb buffer pool is roughly proportional to the size of the pool created. On large installations[*] this initialisation time may be significant.

[*] 2009/10 Initialising a 10 GB buffer pool takes 6 seconds, larger configurations may take proportionally longer.

Posted by K Thomas Kuruvilla on July 16 2012 4:32pm[Delete] [Edit]

It would have been better if the parameters given in here were with concrete examples. I hope it would be done in the future releases.

Posted by Morgan Tocker on November 15 2013 11:34pm[Delete] [Edit]

I wrote a guide for what to tune in MySQL 5.6 after installation here:
http://www.tocker.ca/2013/09/17/what-to-tune-in-mysql-56-after-installation.html