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MySQL 5.5 Reference Manual  /  ...  /  Performance Schema Wait Event Tables

22.9.4 Performance Schema Wait Event Tables

The Performance Schema instruments waits, which are events that take time.

These tables store wait events:

The following sections describe the wait event tables. There are also summary tables that aggregate information about wait events; see Section 22.9.5.1, “Wait Event Summary Tables”.

Wait Event Configuration

To control collection of wait events, set the state of the relevant instruments and consumers:

  • The setup_instruments table contains instruments with names that begin with wait. Use these instruments to enable or disable collection of wait events.

  • The setup_consumers table contains consumer values with names corresponding to the current and recent wait event table names. Use these consumers to filter collection of wait events.

The wait instruments are enabled by default. For example:

mysql> SELECT * FROM setup_instruments
       WHERE NAME LIKE 'wait/io/file/innodb%';
+--------------------------------------+---------+-------+
| NAME                                 | ENABLED | TIMED |
+--------------------------------------+---------+-------+
| wait/io/file/innodb/innodb_data_file | YES     | YES   |
| wait/io/file/innodb/innodb_log_file  | YES     | YES   |
| wait/io/file/innodb/innodb_temp_file | YES     | YES   |
+--------------------------------------+---------+-------+

The wait consumers are enabled by default:

mysql> SELECT * FROM setup_consumers WHERE NAME LIKE '%waits%';
+---------------------------+---------+
| NAME                      | ENABLED |
+---------------------------+---------+
| events_waits_current      | YES     |
| events_waits_history      | YES     |
| events_waits_history_long | YES     |
+---------------------------+---------+

To control wait event collection, update the setup_instruments and setup_consumers tables:

  • Enable:

    UPDATE setup_instruments SET ENABLED = 'YES', TIMED = 'YES'
    WHERE NAME = 'wait/%';
    UPDATE setup_consumers SET ENABLED = 'YES'
    WHERE NAME LIKE '%waits%';
  • Disable:

    UPDATE setup_instruments SET ENABLED = 'NO', TIMED = 'NO'
    WHERE NAME = 'wait/%';
    UPDATE setup_consumers SET ENABLED = 'NO'
    WHERE NAME LIKE '%waits%';

To collect only specific wait events, enable only the corresponding wait instruments. To collect wait events only for specific wait event tables, enable the wait instruments but only the wait consumers corresponding to the desired tables.

The setup_timers table contains a row with a NAME value of wait that indicates the unit for wait event timing. The default unit is CYCLE:

mysql> SELECT * FROM setup_timers WHERE NAME = 'wait';
+------+------------+
| NAME | TIMER_NAME |
+------+------------+
| wait | CYCLE      |
+------+------------+

To change the timing unit, modify the TIMER_NAME value:

UPDATE setup_timers SET TIMER_NAME = 'NANOSECOND'
WHERE NAME = 'wait';

For additional information about configuring event collection, see Section 22.4, “Performance Schema Runtime Configuration”.


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