22.15 Performance Schema System Variables

The Performance Schema implements several system variables that provide configuration information:

mysql> SHOW VARIABLES LIKE 'perf%';
+--------------------------------------------------------+---------+
| Variable_name                                          | Value   |
+--------------------------------------------------------+---------+
| performance_schema                                     | ON      |
| performance_schema_accounts_size                       | 100     |
| performance_schema_digests_size                        | 200     |
| performance_schema_events_stages_history_long_size     | 10000   |
| performance_schema_events_stages_history_size          | 10      |
| performance_schema_events_statements_history_long_size | 10000   |
| performance_schema_events_statements_history_size      | 10      |
| performance_schema_events_waits_history_long_size      | 10000   |
| performance_schema_events_waits_history_size           | 10      |
| performance_schema_hosts_size                          | 100     |
| performance_schema_max_cond_classes                    | 80      |
| performance_schema_max_cond_instances                  | 1000    |
| performance_schema_max_file_classes                    | 50      |
| performance_schema_max_file_handles                    | 32768   |
| performance_schema_max_file_instances                  | 10000   |
| performance_schema_max_mutex_classes                   | 200     |
| performance_schema_max_mutex_instances                 | 1000000 |
| performance_schema_max_rwlock_classes                  | 30      |
| performance_schema_max_rwlock_instances                | 1000000 |
| performance_schema_max_socket_classes                  | 10      |
| performance_schema_max_socket_instances                | 1000    |
| performance_schema_max_stage_classes                   | 150     |
| performance_schema_max_statement_classes               | 165     |
| performance_schema_max_table_handles                   | 10000   |
| performance_schema_max_table_instances                 | 1000    |
| performance_schema_max_thread_classes                  | 50      |
| performance_schema_max_thread_instances                | 1000    |
| performance_schema_session_connect_attrs_size          | 512     |
| performance_schema_setup_actors_size                   | 100     |
| performance_schema_setup_objects_size                  | 100     |
| performance_schema_users_size                          | 100     |
+--------------------------------------------------------+---------+

Performance Schema system variables can be set at server startup on the command line or in option files, and many can be set at runtime. See Section 22.13, “Performance Schema Option and Variable Reference”.

The Performance Schema automatically sizes the values of several of its parameters at server startup if they are not set explicitly. For more information, see Section 22.3, “Performance Schema Startup Configuration”.

Performance Schema system variables have the following meanings:

• performance_schema

  Command-Line Format	--performance-schema[={OFF|ON}]
  System Variable	performance_schema
  Scope	Global
  Dynamic	No
  Type	Boolean
  Default Value	ON

  The value of this variable is ON or OFF to indicate whether the Performance Schema is enabled. By default, the value is ON. At server startup, you can specify this variable with no value or a value of ON or 1 to enable it, or with a value of OFF or 0 to disable it.

• performance_schema_accounts_size

  Command-Line Format	--performance-schema-accounts-size=#
  System Variable	performance_schema_accounts_size
  Scope	Global
  Dynamic	No
  Type	Integer
  Default Value	-1 (signifies autosizing; do not assign this literal value)
  Minimum Value	-1 (signifies autosizing; do not assign this literal value)
  Maximum Value	1048576

  The number of rows in the accounts table. If this variable is 0, the Performance Schema does not maintain connection statistics in the accounts table.

• performance_schema_digests_size

  Command-Line Format	--performance-schema-digests-size=#
  System Variable	performance_schema_digests_size
  Scope	Global
  Dynamic	No
  Type	Integer
  Default Value	-1 (signifies autosizing; do not assign this literal value)
  Minimum Value	-1
  Maximum Value	1048576

  The maximum number of rows in the events_statements_summary_by_digest table. If this maximum is exceeded such that a digest cannot be instrumented, the Performance Schema increments the Performance_schema_digest_lost status variable.

  For more information about statement digesting, see Section 22.10, “Performance Schema Statement Digests”.

• performance_schema_events_stages_history_long_size

  Command-Line Format	--performance-schema-events-stages-history-long-size=#
  System Variable	performance_schema_events_stages_history_long_size
  Scope	Global
  Dynamic	No
  Type	Integer
  Default Value	-1 (signifies autosizing; do not assign this literal value)

  The number of rows in the events_stages_history_long table.

• performance_schema_events_stages_history_size

  Command-Line Format	--performance-schema-events-stages-history-size=#
  System Variable	performance_schema_events_stages_history_size
  Scope	Global
  Dynamic	No
  Type	Integer
  Default Value	-1 (signifies autosizing; do not assign this literal value)

  The number of rows per thread in the events_stages_history table.

• performance_schema_events_statements_history_long_size

  Command-Line Format	--performance-schema-events-statements-history-long-size=#
  System Variable	performance_schema_events_statements_history_long_size
  Scope	Global
  Dynamic	No
  Type	Integer
  Default Value	-1 (signifies autosizing; do not assign this literal value)

  The number of rows in the events_statements_history_long table.

• performance_schema_events_statements_history_size

  Command-Line Format	--performance-schema-events-statements-history-size=#
  System Variable	performance_schema_events_statements_history_size
  Scope	Global
  Dynamic	No
  Type	Integer
  Default Value	-1 (signifies autosizing; do not assign this literal value)

  The number of rows per thread in the events_statements_history table.

• performance_schema_events_waits_history_long_size

  Command-Line Format	--performance-schema-events-waits-history-long-size=#
  System Variable	performance_schema_events_waits_history_long_size
  Scope	Global
  Dynamic	No
  Type	Integer
  Default Value	-1 (signifies autosizing; do not assign this literal value)

  The number of rows in the events_waits_history_long table.

• performance_schema_events_waits_history_size

  Command-Line Format	--performance-schema-events-waits-history-size=#
  System Variable	performance_schema_events_waits_history_size
  Scope	Global
  Dynamic	No
  Type	Integer
  Default Value	-1 (signifies autosizing; do not assign this literal value)

  The number of rows per thread in the events_waits_history table.

• performance_schema_hosts_size

  Command-Line Format	--performance-schema-hosts-size=#
  System Variable	performance_schema_hosts_size
  Scope	Global
  Dynamic	No
  Type	Integer
  Default Value	-1 (signifies autosizing; do not assign this literal value)
  Minimum Value	-1 (signifies autosizing; do not assign this literal value)
  Maximum Value	1048576

  The number of rows in the hosts table. If this variable is 0, the Performance Schema does not maintain connection statistics in the hosts table.

• performance_schema_max_cond_classes

  Command-Line Format	--performance-schema-max-cond-classes=#
  System Variable	performance_schema_max_cond_classes
  Scope	Global
  Dynamic	No
  Type	Integer
  Default Value	80
  Minimum Value	0
  Maximum Value	256

  The maximum number of condition instruments. For information about how to set and use this variable, see Section 22.7, “Performance Schema Status Monitoring”.

• performance_schema_max_cond_instances

  Command-Line Format	--performance-schema-max-cond-instances=#
  System Variable	performance_schema_max_cond_instances
  Scope	Global
  Dynamic	No
  Type	Integer
  Default Value	-1 (signifies autosizing; do not assign this literal value)

  The maximum number of instrumented condition objects. For information about how to set and use this variable, see Section 22.7, “Performance Schema Status Monitoring”.

• performance_schema_max_digest_length

  Command-Line Format	--performance-schema-max-digest-length=#
  Introduced	5.6.26
  System Variable	performance_schema_max_digest_length
  Scope	Global
  Dynamic	No
  Type	Integer
  Default Value	1024
  Minimum Value	0
  Maximum Value	1048576

  The maximum number of bytes of memory reserved per statement for computation of normalized statement digest values in the Performance Schema. This variable is related to max_digest_length; see the description of that variable in Section 5.1.7, “Server System Variables”.

  For more information about statement digesting, including considerations regarding memory use, see Section 22.10, “Performance Schema Statement Digests”.

• performance_schema_max_file_classes

  Command-Line Format	--performance-schema-max-file-classes=#
  System Variable	performance_schema_max_file_classes
  Scope	Global
  Dynamic	No
  Type	Integer
  Default Value	50
  Minimum Value	0
  Maximum Value	256

  The maximum number of file instruments. For information about how to set and use this variable, see Section 22.7, “Performance Schema Status Monitoring”.

• performance_schema_max_file_handles

  Command-Line Format	--performance-schema-max-file-handles=#
  System Variable	performance_schema_max_file_handles
  Scope	Global
  Dynamic	No
  Type	Integer
  Default Value	32768

  The maximum number of opened file objects. For information about how to set and use this variable, see Section 22.7, “Performance Schema Status Monitoring”.

  The value of performance_schema_max_file_handles should be greater than the value of open_files_limit: open_files_limit affects the maximum number of open file handles the server can support and performance_schema_max_file_handles affects how many of these file handles can be instrumented.

• performance_schema_max_file_instances

  Command-Line Format	--performance-schema-max-file-instances=#
  System Variable	performance_schema_max_file_instances
  Scope	Global
  Dynamic	No
  Type	Integer
  Default Value	-1 (signifies autosizing; do not assign this literal value)

  The maximum number of instrumented file objects. For information about how to set and use this variable, see Section 22.7, “Performance Schema Status Monitoring”.

• performance_schema_max_mutex_classes

  Command-Line Format	--performance-schema-max-mutex-classes=#
  System Variable	performance_schema_max_mutex_classes
  Scope	Global
  Dynamic	No
  Type	Integer
  Default Value	200
  Minimum Value	0
  Maximum Value	256

  The maximum number of mutex instruments. For information about how to set and use this variable, see Section 22.7, “Performance Schema Status Monitoring”.

• performance_schema_max_mutex_instances

  Command-Line Format	--performance-schema-max-mutex-instances=#
  System Variable	performance_schema_max_mutex_instances
  Scope	Global
  Dynamic	No
  Type	Integer
  Default Value	-1 (signifies autosizing; do not assign this literal value)

  The maximum number of instrumented mutex objects. For information about how to set and use this variable, see Section 22.7, “Performance Schema Status Monitoring”.

• performance_schema_max_rwlock_classes

  Command-Line Format	--performance-schema-max-rwlock-classes=#
  System Variable	performance_schema_max_rwlock_classes
  Scope	Global
  Dynamic	No
  Type	Integer
  Default Value (≥ 5.6.15)	40
  Default Value (≤ 5.6.14)	30
  Minimum Value	0
  Maximum Value	256

  The maximum number of rwlock instruments. For information about how to set and use this variable, see Section 22.7, “Performance Schema Status Monitoring”.

• performance_schema_max_rwlock_instances

  Command-Line Format	--performance-schema-max-rwlock-instances=#
  System Variable	performance_schema_max_rwlock_instances
  Scope	Global
  Dynamic	No
  Type	Integer
  Default Value	-1 (signifies autosizing; do not assign this literal value)

  The maximum number of instrumented rwlock objects. For information about how to set and use this variable, see Section 22.7, “Performance Schema Status Monitoring”.

• performance_schema_max_socket_classes

  Command-Line Format	--performance-schema-max-socket-classes=#
  System Variable	performance_schema_max_socket_classes
  Scope	Global
  Dynamic	No
  Type	Integer
  Default Value	10
  Minimum Value	0
  Maximum Value	256

  The maximum number of socket instruments. For information about how to set and use this variable, see Section 22.7, “Performance Schema Status Monitoring”.

• performance_schema_max_socket_instances

  Command-Line Format	--performance-schema-max-socket-instances=#
  System Variable	performance_schema_max_socket_instances
  Scope	Global
  Dynamic	No
  Type	Integer
  Default Value	-1 (signifies autosizing; do not assign this literal value)

  The maximum number of instrumented socket objects. For information about how to set and use this variable, see Section 22.7, “Performance Schema Status Monitoring”.

• performance_schema_max_stage_classes

  Command-Line Format	--performance-schema-max-stage-classes=#
  System Variable	performance_schema_max_stage_classes
  Scope	Global
  Dynamic	No
  Type	Integer
  Default Value	150
  Minimum Value	0
  Maximum Value	256

  The maximum number of stage instruments. For information about how to set and use this variable, see Section 22.7, “Performance Schema Status Monitoring”.

• performance_schema_max_statement_classes

  Command-Line Format	--performance-schema-max-statement-classes=#
  System Variable	performance_schema_max_statement_classes
  Scope	Global
  Dynamic	No
  Type	Integer
  Default Value	-1 (signifies autosizing; do not assign this literal value)

  The maximum number of statement instruments. For information about how to set and use this variable, see Section 22.7, “Performance Schema Status Monitoring”.

  The default value is calculated at server build time based on the number of commands in the client/server protocol and the number of SQL statement types supported by the server.

  This variable should not be changed, unless to set it to 0 to disable all statement instrumentation and save all memory associated with it. Setting the variable to nonzero values other than the default has no benefit; in particular, values larger than the default cause more memory to be allocated then is needed.

• performance_schema_max_table_handles

  Command-Line Format	--performance-schema-max-table-handles=#
  System Variable	performance_schema_max_table_handles
  Scope	Global
  Dynamic	No
  Type	Integer
  Default Value	-1 (signifies autosizing; do not assign this literal value)

  The maximum number of opened table objects. For information about how to set and use this variable, see Section 22.7, “Performance Schema Status Monitoring”.

• performance_schema_max_table_instances

  Command-Line Format	--performance-schema-max-table-instances=#
  System Variable	performance_schema_max_table_instances
  Scope	Global
  Dynamic	No
  Type	Integer
  Default Value	-1 (signifies autosizing; do not assign this literal value)

  The maximum number of instrumented table objects. For information about how to set and use this variable, see Section 22.7, “Performance Schema Status Monitoring”.

• performance_schema_max_thread_classes

  Command-Line Format	--performance-schema-max-thread-classes=#
  System Variable	performance_schema_max_thread_classes
  Scope	Global
  Dynamic	No
  Type	Integer
  Default Value	50
  Minimum Value	0
  Maximum Value	256

  The maximum number of thread instruments. For information about how to set and use this variable, see Section 22.7, “Performance Schema Status Monitoring”.

• performance_schema_max_thread_instances

  Command-Line Format	--performance-schema-max-thread-instances=#
  System Variable	performance_schema_max_thread_instances
  Scope	Global
  Dynamic	No
  Type	Integer
  Default Value	-1 (signifies autosizing; do not assign this literal value)

  The maximum number of instrumented thread objects. The value controls the size of the threads table. If this maximum is exceeded such that a thread cannot be instrumented, the Performance Schema increments the Performance_schema_thread_instances_lost status variable. For information about how to set and use this variable, see Section 22.7, “Performance Schema Status Monitoring”.

  The max_connections system variable affects how many threads are run in the server. performance_schema_max_thread_instances affects how many of these running threads can be instrumented. The default value of performance_schema_max_thread_instances is autosized based on the value of max_connections.

• performance_schema_session_connect_attrs_size

  Command-Line Format	--performance-schema-session-connect-attrs-size=#
  System Variable	performance_schema_session_connect_attrs_size
  Scope	Global
  Dynamic	No
  Type	Integer
  Default Value	-1 (signifies autosizing; do not assign this literal value)
  Minimum Value	-1
  Maximum Value	1048576

  The amount of preallocated memory per thread reserved to hold connection attribute key-value pairs. If the aggregate size of connection attribute data sent by a client is larger than this amount, the Performance Schema truncates the attribute data, increments the Performance_schema_session_connect_attrs_lost status variable, and writes a message to the error log indicating that truncation occurred if the log_warnings system variable value is greater than zero.

  The default value of performance_schema_session_connect_attrs_size is autosized at server startup. This value may be small, so if truncation occurs (Performance_schema_session_connect_attrs_lost becomes nonzero), you may wish to set performance_schema_session_connect_attrs_size explicitly to a larger value.

  Although the maximum permitted performance_schema_session_connect_attrs_size value is 1MB, the effective maximum is 64KB because the server imposes a limit of 64KB on the aggregate size of connection attribute data it will accept. If a client attempts to send more than 64KB of attribute data, the server rejects the connection. For more information, see Section 22.12.8, “Performance Schema Connection Attribute Tables”.

• performance_schema_setup_actors_size

  Command-Line Format	--performance-schema-setup-actors-size=#
  System Variable	performance_schema_setup_actors_size
  Scope	Global
  Dynamic	No
  Type	Integer
  Default Value	100

  The number of rows in the setup_actors table.

• performance_schema_setup_objects_size

  Command-Line Format	--performance-schema-setup-objects-size=#
  System Variable	performance_schema_setup_objects_size
  Scope	Global
  Dynamic	No
  Type	Integer
  Default Value	100

  The number of rows in the setup_objects table.

• performance_schema_users_size

  Command-Line Format	--performance-schema-users-size=#
  System Variable	performance_schema_users_size
  Scope	Global
  Dynamic	No
  Type	Integer
  Default Value	-1 (signifies autosizing; do not assign this literal value)
  Minimum Value	-1 (signifies autosizing; do not assign this literal value)
  Maximum Value	1048576

  The number of rows in the users table. If this variable is 0, the Performance Schema does not maintain connection statistics in the users table.