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--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: 

• OFF , FALSE , or 0 : Do not collect events for the consumer 

• ON , TRUE , or 1 : Collect events for the consumer 

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. Consumer names in the setup_consumers  table use underscores, but for consumers set at startup, dashes and underscores within the name are equivalent. 

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

mysql> SHOW VARIABLES LIKE ’perf%’; 

<img src='content_image/868121.jpg'>

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. 

<img src='content_image/868122.jpg'>

<img src='content_image/868123.jpg'>

## Note 

With the Performance Schema enabled, the number of Performance Schema instances affects the server memory footprint, perhaps to a large extent. The Performance Schema autoscales many parameters to use memory only as required; see Section 27.17, “The Performance Schema Memory-Allocation Model” . 

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 for wait events: 

[mysqld] performance_schema performance_schema_events_waits_history_size=20 performance_schema_events_waits_history_long_size=15000 

The Performance Schema automatically sizes the values of several of its parameters at server startup if they are not set explicitly. For example, it sizes the parameters that control the sizes of the events waits tables this way. The Performance Schema allocates memory incrementally, scaling its memory use to actual server load, instead of allocating all the memory it needs during server startup. Consequently, 

