Event Wait Summary Tables

The event waits summary tables aggregate general information about event waits:

• events_waits_summary_global_by_event_name: Wait events summarized per event name
• events_waits_summary_by_instance: Wait events summarized per instance
• events_waits_summary_by_thread_by_event_name: Wait events summarized per thread and event name

For example:

mysql> SELECT * FROM events_waits_summary_global_by_event_name\G
...
*************************** 6. row ***************************
 EVENT_NAME: wait/synch/mutex/sql/MYSQL_BIN_LOG::LOCK_index
 COUNT_STAR: 8
SUM_TIMER_WAIT: 2119302
MIN_TIMER_WAIT: 196092
AVG_TIMER_WAIT: 264912
MAX_TIMER_WAIT: 569421
...
*************************** 9. row ***************************
 EVENT_NAME: wait/synch/mutex/sql/hash_filo::lock
 COUNT_STAR: 69
SUM_TIMER_WAIT: 16848828
MIN_TIMER_WAIT: 0
AVG_TIMER_WAIT: 244185
MAX_TIMER_WAIT: 735345
...

TRUNCATE TABLE is permitted for summary tables. It resets the counters to zero rather than removing rows.

The event wait summary tables have these grouping columns to indicate how events are aggregated:

• events_waits_summary_global_by_event_name has an EVENT_NAME column. Each row summarizes events for a given instrument. An instrument might be used to create multiple instances of the instrumented object. For example, if there is an instrument for a mutex that is created for each connection, there are as many instances as there are connections. The summary row for the instrument summarizes over all these instances.
• events_waits_summary_by_instance has EVENT_NAME and OBJECT_INSTANCE_BEGIN columns. Each row summarizes events for a given instrument instance. If an instrument is used to create multiple instances, each instance has a unique OBJECT_INSTANCE_BEGIN value, so these instances are summarized separately in this table.
• events_waits_summary_by_thread_by_event_name has THREAD_ID and EVENT_NAME columns. Each row summarizes events for a given thread and instrument.

The event waits summary tables have these summary columns containing aggregated values:

• COUNT_STAR

  The number of summarized events. This value includes all events, whether timed or not.

• SUM_TIMER_WAIT

  The total wait time of the summarized timed events. This value is calculated only for timed events because nontimed events have a wait time of NULL. The same is true for the other xxx_TIMER_WAIT values.

• MIN_TIMER_WAIT

  The minimum wait time of the summarized timed events.

• AVG_TIMER_WAIT

  The average wait time of the summarized timed events.

• MAX_TIMER_WAIT

  The maximum wait time of the summarized timed events.

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