MySQL 5.1 Reference Manual  /  ...  /  InnoDB Startup Options and System Variables

14.6.8 InnoDB 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 disable InnoDB 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 as var_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.

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

Table 14.5 InnoDB Option/Variable Reference

NameCmd-LineOption FileSystem VarStatus VarVar ScopeDynamic
foreign_key_checks  Yes SessionYes
have_innodb  Yes GlobalNo
ignore-builtin-innodbYesYes  GlobalNo
- Variable: ignore_builtin_innodb  Yes GlobalNo
innodbYesYes    
innodb_adaptive_flushingYesYesYes GlobalYes
innodb_adaptive_hash_indexYesYesYes GlobalNo
innodb_additional_mem_pool_sizeYesYesYes GlobalNo
innodb_autoextend_incrementYesYesYes GlobalYes
innodb_autoinc_lock_modeYesYesYes GlobalNo
innodb_buffer_pool_awe_mem_mbYesYesYes GlobalNo
Innodb_buffer_pool_pages_data   YesGlobalNo
Innodb_buffer_pool_pages_dirty   YesGlobalNo
Innodb_buffer_pool_pages_flushed   YesGlobalNo
Innodb_buffer_pool_pages_free   YesGlobalNo
Innodb_buffer_pool_pages_latched   YesGlobalNo
Innodb_buffer_pool_pages_misc   YesGlobalNo
Innodb_buffer_pool_pages_total   YesGlobalNo
Innodb_buffer_pool_read_ahead   YesGlobalNo
Innodb_buffer_pool_read_ahead_evicted   YesGlobalNo
Innodb_buffer_pool_read_ahead_rnd   YesGlobalNo
Innodb_buffer_pool_read_ahead_seq   YesGlobalNo
Innodb_buffer_pool_read_requests   YesGlobalNo
Innodb_buffer_pool_reads   YesGlobalNo
innodb_buffer_pool_sizeYesYesYes GlobalNo
Innodb_buffer_pool_wait_free   YesGlobalNo
Innodb_buffer_pool_write_requests   YesGlobalNo
innodb_change_bufferingYesYesYes GlobalYes
innodb_change_buffering_debugYesYesYes GlobalYes
innodb_checksumsYesYesYes GlobalNo
innodb_commit_concurrencyYesYesYes GlobalYes
innodb_concurrency_ticketsYesYesYes GlobalYes
innodb_data_file_pathYesYesYes GlobalNo
Innodb_data_fsyncs   YesGlobalNo
innodb_data_home_dirYesYesYes GlobalNo
Innodb_data_pending_fsyncs   YesGlobalNo
Innodb_data_pending_reads   YesGlobalNo
Innodb_data_pending_writes   YesGlobalNo
Innodb_data_read   YesGlobalNo
Innodb_data_reads   YesGlobalNo
Innodb_data_writes   YesGlobalNo
Innodb_data_written   YesGlobalNo
Innodb_dblwr_pages_written   YesGlobalNo
Innodb_dblwr_writes   YesGlobalNo
innodb_doublewriteYesYesYes GlobalNo
innodb_fast_shutdownYesYesYes GlobalYes
innodb_file_formatYesYesYes GlobalYes
innodb_file_format_checkYesYesYes GlobalYes
innodb_file_io_threadsYesYesYes GlobalNo
innodb_file_per_tableYesYesYes GlobalNo
innodb_flush_log_at_trx_commitYesYesYes GlobalYes
innodb_flush_methodYesYesYes GlobalNo
innodb_force_recoveryYesYesYes GlobalNo
Innodb_have_atomic_builtins   YesGlobalNo
innodb_io_capacityYesYesYes GlobalNo
innodb_limit_optimistic_insert_debugYesYesYes GlobalYes
innodb_lock_wait_timeoutYesYesYes VariesNo
innodb_locks_unsafe_for_binlogYesYesYes GlobalNo
innodb_log_arch_dirYesYesYes GlobalNo
innodb_log_archiveYesYesYes GlobalNo
innodb_log_buffer_sizeYesYesYes GlobalNo
innodb_log_file_sizeYesYesYes GlobalNo
innodb_log_files_in_groupYesYesYes GlobalNo
innodb_log_group_home_dirYesYesYes GlobalNo
Innodb_log_waits   YesGlobalNo
Innodb_log_write_requests   YesGlobalNo
Innodb_log_writes   YesGlobalNo
innodb_max_dirty_pages_pctYesYesYes GlobalYes
innodb_max_purge_lagYesYesYes GlobalYes
innodb_mirrored_log_groupsYesYesYes GlobalNo
innodb_old_blocks_pctYesYesYes GlobalYes
innodb_old_blocks_timeYesYesYes GlobalYes
innodb_open_filesYesYesYes GlobalNo
Innodb_os_log_fsyncs   YesGlobalNo
Innodb_os_log_pending_fsyncs   YesGlobalNo
Innodb_os_log_pending_writes   YesGlobalNo
Innodb_os_log_written   YesGlobalNo
Innodb_page_size   YesGlobalNo
Innodb_pages_created   YesGlobalNo
Innodb_pages_read   YesGlobalNo
Innodb_pages_written   YesGlobalNo
innodb_random_read_aheadYesYesYes GlobalYes
innodb_read_ahead_thresholdYesYesYes GlobalYes
innodb_read_io_threadsYesYesYes GlobalNo
innodb_replication_delayYesYesYes GlobalYes
innodb_rollback_on_timeoutYesYesYes GlobalNo
Innodb_row_lock_current_waits   YesGlobalNo
Innodb_row_lock_time   YesGlobalNo
Innodb_row_lock_time_avg   YesGlobalNo
Innodb_row_lock_time_max   YesGlobalNo
Innodb_row_lock_waits   YesGlobalNo
Innodb_rows_deleted   YesGlobalNo
Innodb_rows_inserted   YesGlobalNo
Innodb_rows_read   YesGlobalNo
Innodb_rows_updated   YesGlobalNo
innodb_spin_wait_delayYesYesYes GlobalYes
innodb_stats_methodYesYesYes GlobalYes
innodb_stats_on_metadataYesYesYes GlobalVaries
innodb_stats_sample_pagesYesYesYes GlobalYes
innodb-status-fileYesYes    
innodb_strict_modeYesYesYes BothYes
innodb_support_xaYesYesYes BothYes
innodb_sync_spin_loopsYesYesYes GlobalYes
innodb_table_locksYesYesYes BothYes
innodb_thread_concurrencyYesYesYes GlobalYes
innodb_thread_sleep_delayYesYesYes GlobalYes
innodb_trx_purge_view_update_only_debugYesYesYes GlobalYes
innodb_trx_rseg_n_slots_debugYesYesYes GlobalYes
innodb_use_legacy_cardinality_algorithmYesYesYes GlobalYes
innodb_use_sys_mallocYesYesYes GlobalNo
innodb_version  Yes GlobalNo
innodb_write_io_threadsYesYesYes GlobalNo
timed_mutexesYesYesYes GlobalYes
unique_checks  Yes SessionYes

InnoDB Command Options

InnoDB System Variables

  • ignore_builtin_innodb

    Introduced5.1.33
    Command-Line Format--ignore-builtin-innodb
    System VariableNameignore_builtin_innodb
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeboolean

    Whether the server was started with the --ignore-builtin-innodb option, which causes the server to behave as if the built-in InnoDB is not present. For more information, see the description of --ignore-builtin-innodb under InnoDB Command Options earlier in this section. This variable was added in MySQL 5.1.33.

  • innodb_adaptive_flushing

    Introduced5.1.38
    Command-Line Format--innodb_adaptive_flushing=#
    System VariableNameinnodb_adaptive_flushing
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultON

    (InnoDB Plugin only) InnoDB Plugin 1.0.4 and up uses a heuristic to determine when to flush dirty pages in the buffer pool. This heuristic is designed to avoid bursts of I/O activity and is used when innodb_adaptive_flushing is enabled (which is the default).

  • innodb_adaptive_hash_index

    Introduced5.1.24
    Command-Line Format--innodb_adaptive_hash_index=#
    System VariableNameinnodb_adaptive_hash_index
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeboolean
    DefaultON

    Whether the InnoDB adaptive hash index is enabled or disabled. The adaptive hash index feature is useful for some workloads, and not for others; conduct benchmarks with it both enabled and disabled, using realistic workloads. See Section 14.6.3.2.4, “Adaptive Hash Indexes” for details. This variable is enabled by default. Use --skip-innodb_adaptive_hash_index at server startup to disable it. This variable was added in MySQL 5.1.24.

  • innodb_additional_mem_pool_size

    Command-Line Format--innodb_additional_mem_pool_size=#
    System VariableNameinnodb_additional_mem_pool_size
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeinteger
    Default1048576
    Min Value524288
    Max Value4294967295

    The size in bytes of a memory pool InnoDB uses to store data dictionary information and other internal data structures. The more tables you have in your application, the more memory you need to allocate here. If InnoDB 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 1MB for the built-in InnoDB, 8MB for InnoDB Plugin.

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

  • innodb_autoextend_increment

    Command-Line Format--innodb_autoextend_increment=#
    System VariableNameinnodb_autoextend_increment
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default8
    Min Value1
    Max Value1000

    The increment size (in MB) for extending the size of an auto-extending shared 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 use innodb_file_per_table=1. Those files are auto-extending regardless of the value of innodb_autoextend_increment. The initial extensions are by small amounts, after which extensions occur in increments of 4MB.

  • innodb_buffer_pool_awe_mem_mb

    Removed5.1.13
    Command-Line Format--innodb_buffer_pool_awe_mem_mb=#
    System VariableNameinnodb_buffer_pool_awe_mem_mb
    Variable ScopeGlobal
    Dynamic VariableNo
    Platform SpecificWindows
    Permitted Values (Windows)Typeinteger
    Default0
    Min Value0
    Max Value63000

    The size of the buffer pool (in MB), if it is placed in the AWE memory. If it is greater than 0, innodb_buffer_pool_size is the window in the 32-bit address space of mysqld where InnoDB maps that AWE memory. A good value for innodb_buffer_pool_size is 500MB. The maximum possible value is 63000.

    To take advantage of AWE memory, you will need to recompile MySQL yourself. The current project settings needed for doing this can be found in the storage/innobase/os/os0proc.c source file.

    This variable was removed in MySQL 5.1.13. Before that, it is relevant only in 32-bit Windows. If your 32-bit Windows operating system supports more than 4GB memory, using so-called Address Windowing Extensions, you can allocate the InnoDB buffer pool into the AWE physical memory using this variable.

  • innodb_autoinc_lock_mode

    Introduced5.1.22
    Command-Line Format--innodb_autoinc_lock_mode=#
    System VariableNameinnodb_autoinc_lock_mode
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeinteger
    Default1
    Valid Values0
    1
    2

    The locking 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 14.6.6.5, “AUTO_INCREMENT Handling in InnoDB”, describes the characteristics of these modes.

    This variable was added in MySQL 5.1.22 with a default of 1 (consecutive lock mode). Before 5.1.22, InnoDB uses traditional lock mode.

  • innodb_buffer_pool_size

    Command-Line Format--innodb_buffer_pool_size=#
    System VariableNameinnodb_buffer_pool_size
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted Values (<= 5.1.27)Typeinteger
    Default8388608
    Min Value1048576
    Permitted Values (32-bit platforms, >= 5.1.28)Typeinteger
    Default134217728
    Min Value1048576
    Max Value2**32-1
    Permitted Values (64-bit platforms, >= 5.1.28)Typeinteger
    Default134217728
    Min Value1048576
    Max Value2**64-1

    The size in bytes of the memory buffer InnoDB uses to cache data and indexes of its tables. The default value is 128MB, increased from a historical default of 8MB. In MySQL 5.1.28 and later, 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.

    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 large installations, 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 8.10.2, “The InnoDB Buffer Pool”.

  • innodb_change_buffering

    Introduced5.1.38
    Command-Line Format--innodb_change_buffering=#
    System VariableNameinnodb_change_buffering
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeenumeration
    Defaultinserts
    Valid Valuesinserts
    none

    (InnoDB Plugin only) Whether InnoDB performs insert buffering. The permitted values none (do not buffer any operations) and inserts (buffer insert operations). The default is inserts. For details, see Section 14.6.3.2.3, “Insert Buffering”.

  • innodb_change_buffering_debug

    Introduced5.1.53
    Command-Line Format--innodb_change_buffering_debug=#
    System VariableNameinnodb_change_buffering_debug
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default0
    Max Value2

    Sets a debug flag for InnoDB change buffering. A value of 1 forces all changes to the change buffer. A value of 2 causes a crash at merge. A default value of 0 indicates that the change buffering debug flag is not set. This option is only available when debugging support is compiled in using the WITH_DEBUG CMake option.

  • innodb_checksums

    Command-Line Format--innodb_checksums
    System VariableNameinnodb_checksums
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeboolean
    DefaultON

    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=#
    System VariableNameinnodb_commit_concurrency
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default0
    Min Value0
    Max Value1000

    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.

    As of MySQL 5.1.36, the value of innodb_commit_concurrency cannot be changed at runtime from zero to nonzero or vice versa. The value can still be changed from one nonzero value to another.

  • innodb_concurrency_tickets

    Command-Line Format--innodb_concurrency_tickets=#
    System VariableNameinnodb_concurrency_tickets
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default500
    Min Value1
    Max Value4294967295

    The number of threads that can enter InnoDB concurrently is determined by the innodb_thread_concurrency variable. A thread is placed in a queue when it tries to enter InnoDB if the number of threads has already reached the concurrency limit. When a thread is permitted to enter InnoDB, it is given a number of free tickets equal to the value of innodb_concurrency_tickets, and the thread can enter and leave InnoDB 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 enter InnoDB. The default value is 500.

    With a small innodb_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 small innodb_concurrency_tickets value is that large transactions must loop through the queue many times before they can complete, which extends the length of time required to complete their task.

    With a large innodb_concurrency_tickets value, large transactions spend less time waiting for a position at the end of the queue (controlled by innodb_thread_concurrency) and more time retrieving rows. Large transactions also require fewer trips through the queue to complete their task. The disadvantage of a large innodb_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 non-zero innodb_thread_concurrency value, you may need to adjust the innodb_concurrency_tickets value up or down to find the optimal balance between larger and smaller transactions. The SHOW ENGINE INNODB STATUS report shows the number of tickets remaining for an executing transaction in its current pass through the queue.

  • innodb_data_file_path

    Command-Line Format--innodb_data_file_path=name
    System VariableNameinnodb_data_file_path
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypestring
    Defaultibdata1:10M:autoextend

    The paths to individual data files and their sizes. The full directory path to each data file is formed by concatenating innodb_data_home_dir to each path specified here. The file sizes are specified MB or GB (1024MB) by appending M or G to the size value. 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, named ibdata1. 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 also use raw disk partitions as data files. For detailed information on configuring InnoDB tablespace files, see Section 14.6.2, “InnoDB Configuration”.

  • innodb_data_home_dir

    Command-Line Format--innodb_data_home_dir=dir_name
    System VariableNameinnodb_data_home_dir
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypedirectory name

    The common part of the directory path for all InnoDB data files in the shared tablespace. This setting does not affect the location of per-file 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 in innodb_data_file_path.

  • innodb_doublewrite

    Command-Line Format--innodb-doublewrite
    System VariableNameinnodb_doublewrite
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeboolean
    DefaultON

    If this variable is enabled (the default), InnoDB stores all data twice, first to the doublewrite 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[=#]
    System VariableNameinnodb_fast_shutdown
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default1
    Valid Values0
    1
    2

    The InnoDB shutdown mode. By default, the value is 1, which causes a fast shutdown (the normal type of shutdown). If the value is 0, InnoDB does a full purge and an insert buffer merge before a shutdown. These operations can take minutes, or even hours in extreme cases. If the value is 1, InnoDB skips these operations at shutdown. If the value is 2, InnoDB will just flush its logs and then shut down cold, as if MySQL had crashed; no committed transaction will be lost, but crash recovery will be done at the next startup. A value of 2 cannot be used on NetWare.

  • innodb_file_format

    Introduced5.1.38
    Command-Line Format--innodb_file_format=#
    System VariableNameinnodb_file_format
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted Values (>= 5.1.38)Typestring
    DefaultAntelope
    Valid ValuesAntelope
    Barracuda

    (InnoDB Plugin only) The file format to use for new InnoDB tables. Currently Antelope and Barracuda are supported. This applies only for tables that have their own tablespace, 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.

  • innodb_file_format_check

    Introduced5.1.38
    Command-Line Format--innodb_file_format_check=#
    System VariableNameinnodb_file_format_check
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted Values (<= 5.1.41)Typestring
    DefaultAntelope
    Permitted Values (>= 5.1.42)Typestring
    DefaultBarracuda

    (InnoDB Plugin only) This variable can be set to 1 or 0 at server startup to enable or disable whether InnoDB checks the file format tag in the shared tablespace (for example, Antelope or Barracuda). If the tag is checked and is higher than that supported by the current version of InnoDB, an error occurs and InnoDB does not start. If the tag is not higher, InnoDB sets the value of innodb_file_format_check to the file format tag, which is the value seen at runtime.

  • innodb_file_io_threads

    Command-Line Format--innodb_file_io_threads=#
    System VariableNameinnodb_file_io_threads
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeinteger
    Default4
    Min Value4
    Max Value64

    The number of file I/O threads in InnoDB. Normally, this should be left at the default value of 4, but disk I/O on Windows may benefit from a larger number. On Unix, increasing the number has no effect; InnoDB always uses the default value.

    With InnoDB Plugin, this variable is unused. Use innodb_read_io_threads and innodb_write_io_threads instead.

  • innodb_file_per_table

    Command-Line Format--innodb_file_per_table
    System VariableNameinnodb_file_per_table
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeboolean
    DefaultOFF

    If innodb_file_per_table is disabled (the default), InnoDB creates tables in the system tablespace. If innodb_file_per_table is enabled, InnoDB creates each new table using its own .ibd file for storing data and indexes, rather than in the system tablespace. See Section 14.6.5.4, “InnoDB File-Per-Table Tablespaces” for information about advantages, disadvantages, and features, such as InnoDB table compression, that only work for tables stored in separate tablespaces.

  • innodb_flush_log_at_trx_commit

    Command-Line Format--innodb_flush_log_at_trx_commit[=#]
    System VariableNameinnodb_flush_log_at_trx_commit
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeenumeration
    Default1
    Valid Values0
    1
    2

    If the value of innodb_flush_log_at_trx_commit is 0, 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. When the value is 1 (the default), the log buffer is written out to the log file at each transaction commit and the flush to disk operation is performed on the log file. When the value is 2, 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.

    The default value of 1 is required for full ACID compliance. You can achieve better performance by setting the value different from 1, but then you can lose up to one second worth of transactions in a crash. With a value of 0, any mysqld process crash can erase the last second of transactions. With a value of 2, only an operating system crash or a power outage can erase the last second of transactions. InnoDB's crash recovery works regardless of the value.

    For the greatest possible durability and consistency in a replication setup using InnoDB with transactions, use innodb_flush_log_at_trx_commit=1 and sync_binlog=1 in your master server my.cnf file.

    Caution

    Many operating systems and some disk hardware fool the flush-to-disk operation. They may tell mysqld that the flush has taken place, even though it has not. Then the durability of transactions is not guaranteed even with the setting 1, and in the worst case a power outage can even corrupt the InnoDB database. 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 command hdparm 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=name
    System VariableNameinnodb_flush_method
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted Values (Unix, <= 5.1.23)Typestring
    DefaultNULL
    Valid Valuesfdatasync
    O_DSYNC
    littlesync
    nosync
    O_DIRECT
    Permitted Values (Unix, >= 5.1.24)Typestring
    DefaultNULL
    Valid Valuesfsync
    littlesync
    nosync
    O_DSYNC
    O_DIRECT
    Permitted Values (Windows)Typestring
    DefaultNULL
    Valid Valuesasync_unbuffered
    normal
    unbuffered

    Defines the method used to flush data to the InnoDB data files and log files, which can affect I/O throughput.

    If innodb_flush_method=NULL on a Unix-like system, the fsync option is used by default. If innodb_flush_method=NULL on Windows, the async_unbuffered option is used by default.

    The innodb_flush_method options for Unix-like systems include:

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

    • O_DSYNC: InnoDB uses O_SYNC to open and flush the log files, and fsync() to flush the data files. InnoDB does not use O_DSYNC directly because there have been problems with it on many varieties of Unix.

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

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

    • O_DIRECT: InnoDB uses O_DIRECT (or directio() on Solaris) to open the data files, and uses fsync() to flush both the data and log files. This option is available on some GNU/Linux versions, FreeBSD, and Solaris.

    The innodb_flush_method options for Windows systems include:

    • async_unbuffered: InnoDB uses Windows asynchronous I/O and non-buffered I/O. async_unbuffered is the default setting on Windows systems.

    • normal: InnoDB uses a simulated asynchronous I/O and buffered I/O. This option is used for internal performance testing and is currently unsupported. Use at your own risk.

    • unbuffered: InnoDB uses a simulated asynchronous I/O and non-buffered I/O. This option is used for internal performance testing and is currently unsupported. Use at your own risk.

    How each settings affects performance depends on hardware configuration and workload. Benchmark your particular configuration to decide which setting to use, or whether to keep the default setting. Examine the Innodb_data_fsyncs status variable to see the overall number of fsync() calls for each setting. The mix of read and write operations in your workload can affect how a setting performs. For example, on a system with a hardware RAID controller and battery-backed write cache, O_DIRECT can help to avoid double buffering between the InnoDB buffer pool and the operating system's file system cache. On some systems where InnoDB data and log files are located on a SAN, the default value or O_DSYNC might be faster for a read-heavy workload with mostly SELECT statements. Always test this parameter with hardware and workload that reflect your production environment.

    Prior to MySQL 5.1.24, the default innodb_flush_method option was named fdatasync. When fdatasync was specified, InnoDB used the fsync() system call to flush both the data and log files. To avoid confusing the fdatasync option name with the fdatasync() system call, the option name was changed to fsync in MySQL 5.1.24.

  • innodb_force_recovery

    Command-Line Format--innodb_force_recovery=#
    System VariableNameinnodb_force_recovery
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeinteger
    Default0
    Min Value0
    Max Value6

    The crash recovery mode. Possible values are from 0 to 6. For the meanings of these values and important information about innodb_force_recovery, see Section 14.6.12.2, “Forcing InnoDB Recovery”.

    Warning

    Only set this variable to a value greater than 0 in an emergency situation, so that you can start InnoDB and dump your tables. As a safety measure, InnoDB prevents INSERT, UPDATE, or DELETE operations when innodb_force_recovery is greater than 0.

  • innodb_io_capacity

    Introduced5.1.38
    Command-Line Format--innodb_io_capacity=#
    System VariableNameinnodb_io_capacity
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted Values (32-bit platforms)Typeinteger
    Default200
    Min Value100
    Max Value2**32-1
    Permitted Values (64-bit platforms)Typeinteger
    Default200
    Min Value100
    Max Value2**64-1

    (InnoDB Plugin only) An upper limit on the I/O activity performed by the InnoDB background tasks, such as flushing 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.

    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 for InnoDB I/O, particularly fast drives capable of high numbers of IOPS. For example, systems that use multiple disks or solid-state disks for InnoDB 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 is 200. You can set the value of this parameter in the MySQL option file (my.cnf or my.ini) or change it dynamically with the SET GLOBAL command, which requires the SUPER privilege.

    See Configuring the InnoDB Master Thread I/O Rate for more guidelines about this option. For general information about InnoDB I/O performance, see Section 8.6.7, “Optimizing InnoDB Disk I/O”.

    This variable was added in MySQL 5.1.38.

  • innodb_limit_optimistic_insert_debug

    Introduced5.1.68
    Command-Line Format--innodb_limit_optimistic_insert_debug=#
    System VariableNameinnodb_limit_optimistic_insert_debug
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default0
    Min Value0
    Max Value2**32-1

    Limits the number of records per B-tree page. A default value of 0 means that no limit is imposed. This option is only available if debugging support is compiled in using the WITH_DEBUG CMake option.

  • innodb_lock_wait_timeout

    Command-Line Format--innodb_lock_wait_timeout=#
    System Variable (<= 5.1.37)Nameinnodb_lock_wait_timeout
    Variable ScopeGlobal
    Dynamic VariableNo
    System Variable (>= 5.1.38)Nameinnodb_lock_wait_timeout
    Variable ScopeGlobal, Session
    Dynamic VariableNo
    Permitted ValuesTypeinteger
    Default50
    Min Value1
    Max Value1073741824

    The timeout 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 another InnoDB 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 14.6.12.4, “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.

    InnoDB does detect transaction deadlocks in its own lock table immediately and rolls back one transaction. The lock wait timeout value does not apply to such a wait.

    For the built-in InnoDB, this variable can be set only at server startup. For InnoDB Plugin, it can be set at startup or changed at runtime, and has both global and session values.

  • innodb_locks_unsafe_for_binlog

    Command-Line Format--innodb_locks_unsafe_for_binlog
    System VariableNameinnodb_locks_unsafe_for_binlog
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeboolean
    DefaultOFF

    This variable affects how InnoDB uses gap locking for searches and index scans. Normally, InnoDB uses an algorithm called next-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 before R in the index order. See Section 14.6.4.2, “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 to READ 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 than innodb_locks_unsafe_for_binlog. For additional details about the effect of isolation level on gap locking, see Section 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 the id 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 same SELECT 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, if innodb_locks_unsafe_for_binlog is enabled, InnoDB guarantees at most an isolation level of READ COMMITTED. (Conflict serializability is still guaranteed.) For additional information about phantoms, see Section 14.6.4.3, “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 the WHERE 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 the WHERE condition of the UPDATE. If the row matches (must be updated), MySQL reads the row again and this time InnoDB 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 (see Section 14.6.3.2.1, “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. If InnoDB 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 first UPDATE acquires x-locks and does not release any of them:

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

    For the second UPDATE, 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 the WHERE condition of the UPDATE:

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

    Semi-consistent read is available as of MySQL 5.1.5. Before 5.1.5, the second UPDATE proceeds part way before it blocks. It begins acquiring x-locks, and blocks when it tries to acquire one for a row still locked by first UPDATE. The second UPDATE does not proceed until the first UPDATE commits or rolls back:

    x-lock(1,2); update(1,2) to (1,4); retain x-lock
    x-lock(2,3); block and wait for first UPDATE to commit or roll back
    

    In this case, the second UPDATE must wait for a commit or rollback of the first UPDATE, even though it affects different rows. The first UPDATE has an exclusive lock on row (2,3) that it has not released. As the second UPDATE scans rows, it tries to acquire an exclusive lock for that same row, which it cannot have. Thus, before MySQL 5.1.5, enabling innodb_locks_unsafe_for_binlog still does not permit operations such as UPDATE to overtake other similar operations (such as another UPDATE) even when they affect different rows.

  • innodb_log_arch_dir

    This variable is deprecated, and was removed in MySQL 5.1.21.

  • innodb_log_archive

    This variable is deprecated, and was removed in MySQL 5.1.18.

  • innodb_log_buffer_size

    Command-Line Format--innodb_log_buffer_size=#
    System VariableNameinnodb_log_buffer_size
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeinteger
    Default1048576
    Min Value1048576
    Max Value4294967295

    The size in bytes of the buffer that InnoDB uses to write to the log files on disk. The default value is 1MB for the built-in InnoDB, 8MB for InnoDB Plugin. Sensible values range from 1MB to 8MB. A large log buffer enables large transactions to run without a need to write the log to disk before the transactions commit. Thus, if you have big transactions, making the log buffer larger saves disk I/O.

  • innodb_log_file_size

    Command-Line Format--innodb_log_file_size=#
    System VariableNameinnodb_log_file_size
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeinteger
    Default5242880
    Min Value1048576
    Max Value4GB / 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, where N 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. But larger log files also mean that recovery is slower in case of a crash.

  • innodb_log_files_in_group

    Command-Line Format--innodb_log_files_in_group=#
    System VariableNameinnodb_log_files_in_group
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeinteger
    Default2
    Min Value2
    Max Value100

    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.

  • innodb_log_group_home_dir

    Command-Line Format--innodb_log_group_home_dir=dir_name
    System VariableNameinnodb_log_group_home_dir
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypedirectory name

    The directory path to the InnoDB log files. If you do not specify any InnoDB log variables, the default is to create two files named ib_logfile0 and ib_logfile1 in the MySQL data directory. Their size is given by the size of the innodb_log_file_size system variable.

  • innodb_max_dirty_pages_pct

    Command-Line Format--innodb_max_dirty_pages_pct=#
    System VariableNameinnodb_max_dirty_pages_pct
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypenumeric
    Default90
    Min Value0
    Max Value100

    This is an integer in the range from 0 to 100. The default value is 90 for the built-in InnoDB, 75 for InnoDB Plugin. The main thread in InnoDB tries to write pages from the buffer pool so that the percentage of dirty (not yet written) pages will not exceed this value.

  • innodb_max_purge_lag

    Command-Line Format--innodb_max_purge_lag=#
    System VariableNameinnodb_max_purge_lag
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default0
    Min Value0
    Max Value4294967295

    This variable controls how to delay INSERT, UPDATE, and DELETE operations when purge operations are lagging (see Section 14.6.3.1, “InnoDB Multi-Versioning”). The default value 0 (no delays).

    The InnoDB transaction system maintains a list of transactions that have index records delete-marked by UPDATE or DELETE operations. Let the length of this list be purge_lag. When purge_lag exceeds innodb_max_purge_lag, each INSERT, 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 old consistent 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 unpurged InnoDB 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 290328385
    Purge done for trx's n:o < 0 290315608 undo n:o < 0 17
    History list length 20
    
  • innodb_mirrored_log_groups

    Has no effect.

  • innodb_old_blocks_pct

    Introduced5.1.41
    Command-Line Format--innodb_old_blocks_pct=#
    System VariableNameinnodb_old_blocks_pct
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default37
    Min Value5
    Max Value95

    (InnoDB Plugin only) Specifies the approximate percentage of the InnoDB buffer 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). See Section 8.10.2, “The InnoDB Buffer Pool” for information about buffer pool management, such as the LRU algorithm and eviction policies.

    This variable was added in MySQL 5.1.41.

  • innodb_old_blocks_time

    Introduced5.1.41
    Command-Line Format--innodb_old_blocks_time=#
    System VariableNameinnodb_old_blocks_time
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default0
    Min Value0
    Max Value2**32-1

    (InnoDB Plugin only) 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. The default 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 8.10.2, “The InnoDB Buffer Pool” for information about buffer pool management, such as the LRU algorithm and eviction policies.

    This variable was added in MySQL 5.1.41.

  • innodb_open_files

    Command-Line Format--innodb_open_files=#
    System VariableNameinnodb_open_files
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeinteger
    Default300
    Min Value10
    Max Value4294967295

    This variable is relevant only if you use multiple InnoDB tablespaces. 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 for InnoDB 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_random_read_ahead

    Introduced5.1.59
    Command-Line Format--innodb_random_read_ahead=#
    System VariableNameinnodb_random_read_ahead
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    Enables the random read-ahead technique for optimizing InnoDB I/O. Random read-ahead functionality was removed from the InnoDB Plugin (version 1.0.4) and was therefore not included in MySQL 5.5.0 when InnoDB Plugin became the built-in version of InnoDB. Random read-ahead was reintroduced in MySQL 5.1.59 and 5.5.16 and higher along with the innodb_random_read_ahead configuration option, which is disabled by default.

    See 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, see Section 8.6.7, “Optimizing InnoDB Disk I/O”.

  • innodb_read_ahead_threshold

    Introduced5.1.38
    Command-Line Format--innodb_read_ahead_threshold=#
    System VariableNameinnodb_read_ahead_threshold
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default56
    Min Value0
    Max Value64

    (InnoDB Plugin only) Controls the sensitivity of linear read-ahead that InnoDB uses to prefetch pages into the buffer pool. If InnoDB reads at least innodb_read_ahead_threshold pages sequentially from an extent (64 pages), it initiates an asynchronous read for the entire following extent. The permissible range of values is 0 to 64. The default is 56: InnoDB must read at least 56 pages sequentially from an extent to initiate an asynchronous read for the following extent.

    This variable was added in MySQL 5.1.38.

  • innodb_read_io_threads

    Introduced5.1.38
    Command-Line Format--innodb_read_io_threads=#
    System VariableNameinnodb_read_io_threads
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeinteger
    Default4
    Min Value1
    Max Value64

    (InnoDB Plugin only) The number of I/O threads for read operations in InnoDB. The default value is 4.

    Note

    On Linux systems, running multiple MySQL servers (typically more than 12) with default settings for innodb_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.

    This variable was added in MySQL 5.1.38.

  • innodb_replication_delay

    Introduced5.1.38
    Command-Line Format--innodb_replication_delay=#
    System VariableNameinnodb_replication_delay
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default0
    Min Value0
    Max Value4294967295

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

    This variable was added in MySQL 5.1.38.

  • innodb_rollback_on_timeout

    Introduced5.1.15
    Command-Line Format--innodb_rollback_on_timeout
    System VariableNameinnodb_rollback_on_timeout
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeboolean
    DefaultOFF

    In MySQL 5.1, InnoDB rolls back only the last statement on a transaction timeout by default. If --innodb_rollback_on_timeout is specified, a transaction timeout causes InnoDB to abort and roll back the entire transaction (the same behavior as in MySQL 4.1). This variable was added in MySQL 5.1.15.

  • innodb_spin_wait_delay

    Introduced5.1.38
    Command-Line Format--innodb_spin_wait_delay=#
    System VariableNameinnodb_spin_wait_delay
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default6
    Min Value0
    Max Value4294967295

    (InnoDB Plugin only) 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.

    This variable was added in MySQL 5.1.38.

  • innodb_stats_method

    Introduced5.1.56
    Command-Line Format--innodb_stats_method=name
    System VariableNameinnodb_stats_method
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeenumeration
    Defaultnulls_equal
    Valid Valuesnulls_equal
    nulls_unequal
    nulls_ignored

    How the server treats NULL values when collecting statistics about the distribution of index values for InnoDB tables. This variable has three possible values, nulls_equal, nulls_unequal, and nulls_ignored. For nulls_equal, all NULL index values are considered equal and form a single value group that has a size equal to the number of NULL values. For nulls_unequal, NULL values are considered unequal, and each NULL 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 in Section 8.3.7, “InnoDB and MyISAM Index Statistics Collection”.

  • innodb_stats_on_metadata

    Introduced5.1.17
    Command-Line Format--innodb_stats_on_metadata
    System Variable (<= 5.1.31)Nameinnodb_stats_on_metadata
    Variable ScopeGlobal
    Dynamic VariableNo
    System Variable (>= 5.1.32)Nameinnodb_stats_on_metadata
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultON

    When this variable is enabled (which is the default, as before the variable was created), InnoDB updates statistics during metadata statements such as SHOW TABLE STATUS or SHOW INDEX, or when accessing the INFORMATION_SCHEMA tables TABLES or STATISTICS. (These updates are similar to what happens for ANALYZE 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 of execution plans for queries that involve InnoDB tables.

    This variable was added in MySQL 5.1.17.

  • innodb_stats_sample_pages

    Introduced5.1.38
    Command-Line Format--innodb_stats_sample_pages=#
    System VariableNameinnodb_stats_sample_pages
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default8
    Min Value1
    Max Value2**64-1

    (InnoDB Plugin only) The number of index pages to sample for index distribution statistics such as are calculated by ANALYZE TABLE. The default value is 8.

    This variable was added in MySQL 5.1.38.

  • innodb_strict_mode

    Introduced5.1.38
    Command-Line Format--innodb_strict_mode=#
    System VariableNameinnodb_strict_mode
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

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

    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 is ON, InnoDB raises error conditions in certain cases, rather than issuing a warning and processing the specified statement (perhaps with unintended behavior). This is analogous to sql_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 for CREATE TABLE, ALTER TABLE and CREATE INDEX statements. innodb_strict_mode also enables a record size check, so that an INSERT or UPDATE never fails due to the record being too large for the selected page size.

    Oracle recommends enabling innodb_strict_mode when using ROW_FORMAT and KEY_BLOCK_SIZE clauses on CREATE 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 statement SET [GLOBAL|SESSION] innodb_strict_mode=mode, where mode is either ON or OFF. Changing the GLOBAL setting requires the SUPER privilege and affects the operation of all clients that subsequently connect. Any client can change the SESSION setting for innodb_strict_mode, and the setting affects only that client.

  • innodb_support_xa

    Command-Line Format--innodb_support_xa
    System VariableNameinnodb_support_xa
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultTRUE

    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 for InnoDB 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=#
    System VariableNameinnodb_sync_spin_loops
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default20
    Min Value0
    Max Value4294967295

    The number of times a thread waits for an InnoDB mutex to be freed before the thread is suspended. The default value is 20 for the built-in InnoDB, 30 for InnoDB Plugin.

  • innodb_table_locks

    Command-Line Format--innodb_table_locks
    System VariableNameinnodb_table_locks
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultTRUE

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

  • innodb_thread_concurrency

    Command-Line Format--innodb_thread_concurrency=#
    System VariableNameinnodb_thread_concurrency
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default8
    Min Value0
    Max Value1000

    InnoDB tries to keep the number of operating system threads concurrently inside InnoDB less than or equal to the limit given by this variable (InnoDB uses operating system threads to process user transactions). Once the number of threads reaches this limit, additional threads are placed into a wait state within a First In, First Out (FIFO) queue for execution. Threads waiting for locks are not counted in the number of concurrently executing threads.

    The range of this variable is 0 to 1000. A value of 20 or higher is interpreted as infinite concurrency before MySQL 5.1.12. From 5.1.12 on, you can disable thread concurrency checking by setting the value to 0. Disabling thread concurrency checking enables InnoDB to create as many threads as it needs. A value of 0 also disables the queries inside InnoDB and queries in queue counters in the ROW OPERATIONS section of SHOW ENGINE INNODB STATUS output.

    The default value for the built-in InnoDB is 20 before MySQL 5.1.11 and 8 from 5.1.11 on. The default for the InnoDB Plugin is 0.

    Consider setting this variable if your MySQL instance shares CPU resources with other applications, or if your workload or number of concurrent users is growing. The correct setting depends on workload, computing environment, and the version of MySQL that you are running. You will need to test a range of values to determine the setting that provides the best performance. innodb_thread_concurrency is a dynamic variable, which allows you to experiment with different settings on a live test system. If a particular setting performs poorly, you can quickly set innodb_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 less than 64, set innodb_thread_concurrency=0.

    • If your workload is consistently heavy or occasionally spikes, start by setting innodb_thread_concurrency=128, and lowering the value to 96, 80, 64, and so on, until you find the number of threads that provides the best performance. For example, suppose your system typically has 40 to 50 users, but periodically the number increases to 60, 70, or even 200. You find that performance is stable at 80 concurrent users but starts to show a regression above this number. In this case, you would set innodb_thread_concurrency=80 to avoid impacting performance.

    • If you do not want InnoDB to use more than a certain number of vCPUs for user threads (20 vCPUs for example), set innodb_thread_concurrency to this number (or possibly lower, depending on performance results). If your goal is to isolate MySQL from other applications, you may consider binding the mysqld process exclusively to the vCPUs. Be aware, however, that exclusive binding could result in non-optimal hardware usage if the mysqld process is not consistently busy. In this case, you might bind the mysqld process to the vCPUs but also allow other applications to use some or all of the vCPUs.

      Note

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

    • innodb_thread_concurrency values that are too high can cause performance regression due to increased contention on system internals and resources.

    • In some cases, the optimal innodb_thread_concurrency setting can be smaller than the number of vCPUs.

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

  • innodb_thread_sleep_delay

    Command-Line Format--innodb_thread_sleep_delay=#
    System VariableNameinnodb_thread_sleep_delay
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted Values (32-bit platforms)Typeinteger
    Default10000
    Min Value0
    Max Value4294967295
    Permitted Values (64-bit platforms)Typeinteger
    Default10000
    Min Value0
    Max Value18446744073709551615

    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_trx_purge_view_update_only_debug

    Introduced5.1.68
    Command-Line Format--innodb_trx_purge_view_update_only_debug=#
    System VariableNameinnodb_trx_purge_view_update_only_debug
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    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 the WITH_DEBUG CMake option.

  • innodb_trx_rseg_n_slots_debug

    Introduced5.1.62
    Command-Line Format--innodb_trx_rseg_n_slots_debug=#
    System VariableNameinnodb_trx_rseg_n_slots_debug
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default0
    Max Value1024

    Sets a debug flag that limits TRX_RSEG_N_SLOTS to a given value for the trx_rsegf_undo_find_free function which looks for a free slot for an undo log segment. This option is only available if debugging support is compiled in using the WITH_DEBUG CMake option.

  • innodb_use_legacy_cardinality_algorithm

    Introduced5.1.35
    Command-Line Format--innodb_use_legacy_cardinality_algorithm=#
    System VariableNameinnodb_use_legacy_cardinality_algorithm
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultON

    InnoDB uses random numbers to generate dives into indexes for calculating index cardinality. However, under certain conditions, the algorithm does not generate random numbers, so ANALYZE TABLE sometimes does not update cardinality estimates properly. An alternative algorithm was introduced in MySQL 5.1.35 with better randomization properties, and the innodb_use_legacy_cardinality_algorithm, system variable which algorithm to use. The default value of the variable is 1 (ON), to use the original algorithm for compatibility with existing applications. The variable can be set to 0 (OFF) to use the new algorithm with improved randomness.

    This variable is not used in InnoDB Plugin because the improved algorithm is used by default. Also, the number of random dives can be changed by modifying the innodb_stats_sample_pages system variable.

  • innodb_use_sys_malloc

    Introduced5.1.38
    Command-Line Format--innodb_use_sys_malloc=#
    System VariableNameinnodb_use_sys_malloc
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeboolean
    DefaultON

    (InnoDB Plugin only) Whether InnoDB uses the operating system memory allocator (ON) or its own (OFF). The default value is ON.

    This variable was added in MySQL 5.1.38.

  • innodb_version

    (InnoDB Plugin only) The InnoDB version number. Starting in 5.1.68, the separate numbering for InnoDB is discontinued and this value is the same as for the version variable.

    This variable was added in MySQL 5.1.38.

  • innodb_write_io_threads

    Introduced5.1.38
    Command-Line Format--innodb_write_io_threads=#
    System VariableNameinnodb_write_io_threads
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeinteger
    Default4
    Min Value1
    Max Value64

    (InnoDB Plugin only) The number of I/O threads for write operations in InnoDB. The default value is 4.

    Note

    On Linux systems, running multiple MySQL servers (typically more than 12) with default settings for innodb_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.

    This variable was added in MySQL 5.1.38.

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


User Comments
  Posted by Morgan Tocker on December 28, 2006
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 Brian Aker on August 16, 2007
Commentary on Innodb parameters for an 8way machine:
http://krow.livejournal.com/542306.html
  Posted by Willem de Groot on September 20, 2007
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
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 Morgan Tocker on November 15, 2013
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
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