21.7.4. Performance Schema Summary Tables

Summary tables provide aggregate information for terminated events over time. The tables in this group summarize event data in different ways.

This group contains tables with names that match the pattern '%summary%':

mysql> SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES
    -> WHERE TABLE_SCHEMA = 'performance_schema'
    -> AND TABLE_NAME LIKE '%summary%';
+----------------------------------------------+
| TABLE_NAME                                   |
+----------------------------------------------+
| events_waits_summary_by_instance             |
| events_waits_summary_by_thread_by_event_name |
| events_waits_summary_global_by_event_name    |
| file_summary_by_event_name                   |
| file_summary_by_instance                     |
+----------------------------------------------+

The events_waits_summary_global_by_event_name table was named EVENTS_WAITS_SUMMARY_BY_EVENT_NAME before MySQL 5.5.7.

Each summary table contains columns to hold aggregated information, and columns that show the groupings for which the aggregated values were computed. Tables that summarize events in similar ways have similar sets of columns, differing only in the columns that show what the groupings are.

Summary tables can be truncated with TRUNCATE TABLE. The effect is to reset the summary columns to 0 or NULL, not to remove rows. This enables you to clear collected values and restart aggregation. That might be useful, for example, after you have made a runtime configuration change.

events_waits_summary_by_xxx tables have these columns in common:

  • COUNT_STAR

    The number of summarized events. This value includes all events, whether timed or not.

  • 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 values.

  • 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.

The remaining columns in the events_waits_summary_by_xxx tables indicate how events were aggregated:

  • events_waits_summary_global_by_event_name has an EVENT_NAME column. Each row summarizes events for a given instrument. 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.

  • events_waits_summary_by_instance has EVENT_NAME and OBJECT_INSTANCE_BEGIN columns. Each row summarizes events for a given instrument instance. 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 instrument.

file_summary_by_xxx tables have these columns in common:

  • COUNT_READ

    The number of read operations in the summarized events.

  • COUNT_WRITE

    The number of write operations in the summarized events.

  • SUM_NUMBER_OF_BYTES_READ

    The number of bytes read in the summarized events.

  • SUM_NUMBER_OF_BYTES_WRITE

    The number of bytes written in the summarized events.

The remaining columns in the file_summary_by_xxx tables indicate how events were aggregated:

  • file_summary_by_event_name has an EVENT_NAME column. Each row summarizes events for a given instrument.

  • file_summary_by_instance has FILE_NAME and EVENT_NAME columns. Each row summarizes events for a given file.

Example:

mysql> SELECT * FROM events_waits_summary_global_by_event_name\G
...
*************************** 6. row ***************************
    EVENT_NAME: wait/synch/mutex/sql/MYSQL_BIN_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
...
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