The Performance Schema is disabled by default. To enable it, start the server with the performance_schema variable enabled. For example, use these lines in your my.cnf file:

[mysqld]
performance_schema

When the server starts, it writes Performance Schema status information to the error log:

If the server is unable to allocate any internal buffer during Performance Schema initialization, the Performance Schema disables itself and sets performance_schema to OFF, and the server runs without instrumentation.

As of MySQL 5.6.4, the Performance Schema permits instrument and consumer configuration at server startup, which previously was possible only at runtime using UPDATE statements for the setup_instruments and setup_consumers tables. This change was made because configuration at runtime is too late to disable instruments that have already been initialized during server startup. For example, the wait/sync/mutex/sql/LOCK_open mutex is initialized once during server startup, so attempts to disable the corresponding instrument at runtime have no effect.

To control an instrument at server startup, use an option of this form:

--performance_schema_instrument='instrument_name=value'

Here, instrument_name is an instrument name such as wait/sync/mutex/sql/LOCK_open, and value is one of these values:

Each --performance_schema_instrument option can specify only one instrument name, but multiple instances of the option can be given to configure multiple instruments. In addition, patterns are permitted in instrument names to configure instruments that match the pattern. To configure all condition synchronization instruments as enabled and counted, use this option:

--performance_schema_instrument='wait/synch/cond/%=counted'

To disable all instruments, use this option:

--performance_schema_instrument='%=off'

Longer instrument name strings take precedence over shorter pattern names, regardless of order. For information about specifying patterns to select instruments, see Section 20.2.3.2.2, “Naming Instruments or Consumers for Filtering Operations”.

An unrecognized instrument name is ignored. It is possible that a plugin installed later may create the instrument, at which time the name is recognized and configured.

To control a consumer at server startup, use an option of this form:

--performance_schema_consumer_consumer_name=value

Here, consumer_name is a consumer name such as events_waits_history, and value is one of these values:

For example, to enable the events_waits_history consumer, use this option:

--performance_schema_consumer_events_waits_history=on

The permitted consumer names can be found by examining the setup_consumers table. Patterns are not permitted.

The Performance Schema includes 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    |
...

The performance_schema variable is ON or OFF to indicate whether the Performance Schema is enabled or disabled. The other variables indicate table sizes (number of rows) or memory allocation values.

To change the value of Performance Schema system variables, set them at server startup. For example, put the following lines in a my.cnf file to change the sizes of the history tables:

[mysqld]
performance_schema
performance_schema_events_waits_history_size=20
performance_schema_events_waits_history_long_size=15000