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MySQL 5.7 Reference Manual
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The Performance Schema maintains tables for collecting current and recent stage events, and aggregates that information in summary tables. Section 21.9.5, “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 recent stage event tables, and how to control stage event collection.

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.

All stage summary tables have 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 event wait summary tables (see Section, “Event Wait Summary Tables”), except that the stage summary tables aggregate events from events_stages_current rather than events_waits_current.

Example stage event summary information:

mysql> SELECT * FROM events_stages_summary_global_by_event_name\G
*************************** 5. row ***************************
    EVENT_NAME: stage/sql/checking permissions
    COUNT_STAR: 57
SUM_TIMER_WAIT: 26501888880
AVG_TIMER_WAIT: 464945295
MAX_TIMER_WAIT: 12858936792
*************************** 9. row ***************************
    EVENT_NAME: stage/sql/closing tables
    COUNT_STAR: 37
SUM_TIMER_WAIT: 662606568
AVG_TIMER_WAIT: 17907891
MAX_TIMER_WAIT: 437977248

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

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