The Performance Schema maintains tables for collecting current and recent wait events, and aggregates that information in summary tables. Section 22.10.4, “Performance Schema Wait Event Tables” describes the events on which wait summaries are based. See that discussion for information about the content of wait events, the current and recent wait event tables, and how to control wait event collection.
Example wait event summary information:
mysql> SELECT * FROM performance_schema.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
...
Each wait event summary table has one or more grouping columns
to indicate how the table aggregates events. Event names refer
to names of event instruments in the
setup_instruments
table:
events_waits_summary_by_instance
hasEVENT_NAME
andOBJECT_INSTANCE_BEGIN
columns. Each row summarizes events for a given event name and object. If an instrument is used to create multiple instances, each instance has a uniqueOBJECT_INSTANCE_BEGIN
value, so these instances are summarized separately in this table.events_waits_summary_by_thread_by_event_name
hasTHREAD_ID
andEVENT_NAME
columns. Each row summarizes events for a given thread and event name.events_waits_summary_global_by_event_name
has anEVENT_NAME
column. Each row summarizes events for a given event name. 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.
Each wait event summary table has these summary columns containing aggregated values:
COUNT_STAR
The number of summarized events. This value includes all events, whether timed or nontimed.
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
values.xxx
_TIMER_WAITMIN_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.
TRUNCATE TABLE
is permitted for
wait summary tables. It resets the summary columns to zero
rather than removing rows.