MySQL 5.6 Reference Manual Including MySQL NDB Cluster 7.3-7.4 Reference Guide
The Performance Schema maintains tables for collecting current and recent stage events, and aggregates that information in summary tables. Section 22.12.5, “Performance Schema Stage Event Tables” describes the events on which stage summaries are based. See that discussion for information about the content of stage events, the current and historical stage event tables, and how to control stage event collection, which is disabled by default.
Example stage event summary information:
mysql>SELECT *
FROM performance_schema.events_stages_summary_global_by_event_name\G
... *************************** 5. row *************************** EVENT_NAME: stage/sql/checking permissions COUNT_STAR: 57 SUM_TIMER_WAIT: 26501888880 MIN_TIMER_WAIT: 7317456 AVG_TIMER_WAIT: 464945295 MAX_TIMER_WAIT: 12858936792 ... *************************** 9. row *************************** EVENT_NAME: stage/sql/closing tables COUNT_STAR: 37 SUM_TIMER_WAIT: 662606568 MIN_TIMER_WAIT: 1593864 AVG_TIMER_WAIT: 17907891 MAX_TIMER_WAIT: 437977248 ...
Each stage 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_stages_summary_by_account_by_event_name
has EVENT_NAME
,
USER
, and HOST
columns. Each row summarizes events for a given account
(user and host combination) and event name.
events_stages_summary_by_host_by_event_name
has EVENT_NAME
and
HOST
columns. Each row summarizes
events for a given host and event name.
events_stages_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_stages_summary_by_user_by_event_name
has EVENT_NAME
and
USER
columns. Each row summarizes
events for a given user and event name.
events_stages_summary_global_by_event_name
has an EVENT_NAME
column. Each row
summarizes events for a given event name.
Each stage summary table has these summary columns containing
aggregated values: COUNT_STAR
,
SUM_TIMER_WAIT
,
MIN_TIMER_WAIT
,
AVG_TIMER_WAIT
, and
MAX_TIMER_WAIT
. These columns are analogous
to the columns of the same names in the wait event summary
tables (see Section 22.12.9.1, “Wait Event Summary Tables”), except
that the stage summary tables aggregate events from
events_stages_current
rather than
events_waits_current
.
TRUNCATE TABLE
is permitted for
stage summary tables. It has these effects:
For summary tables not aggregated by account, host, or user, truncation resets the summary columns to zero rather than removing rows.
For summary tables aggregated by account, host, or user, truncation removes rows for accounts, hosts, or users with no connections, and resets the summary columns to zero for the remaining rows.
In addition, each stage summary table that is aggregated by
account, host, user, or thread is implicitly truncated by
truncation of the connection table on which it depends, or
truncation of
events_stages_summary_global_by_event_name
.
For details, see
Section 22.12.7, “Performance Schema Connection Tables”.