- 21.7.4 Performance Schema Summary Tables
- 21.7.4.1 Event Wait Summary Tables
- 21.7.4.2 File I/O 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 nameevents_waits_summary_by_instance: Wait events summarized per instanceevents_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/BINARY_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
wait 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_namehas anEVENT_NAMEcolumn. 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_instancehasEVENT_NAMEandOBJECT_INSTANCE_BEGINcolumns. Each row summarizes events for a given instrument instance. If an instrument is used to create multiple instances, each instance has a uniqueOBJECT_INSTANCE_BEGINvalue, so these instances are summarized separately in this table.events_waits_summary_by_thread_by_event_namehasTHREAD_IDandEVENT_NAMEcolumns. Each row summarizes events for a given thread and instrument.
The event waits summary tables have these summary columns containing aggregated values:
COUNT_STARThe number of summarized events. This value includes all events, whether timed or not.
SUM_TIMER_WAITThe 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 otherxxx_TIMER_WAITMIN_TIMER_WAITThe minimum wait time of the summarized timed events.
AVG_TIMER_WAITThe average wait time of the summarized timed events.
MAX_TIMER_WAITThe maximum wait time of the summarized timed events.
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