The Performance Schema maintains tables for collecting current and recent wait events, and aggregates that information in summary tables. Section 22.8.4, “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 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
has EVENT_NAME and
OBJECT_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 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 event name.
events_waits_summary_global_by_event_name
has an EVENT_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
xxx_TIMER_WAIT
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.
TRUNCATE TABLE is permitted for
wait summary tables. It resets the summary columns to zero
rather than removing rows.