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26.12.17.7 File I/O Summary Tables

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The Performance Schema maintains file I/O summary tables that aggregate information about I/O operations.

Example file I/O event summary information:

  1. mysql> SELECT * FROM performance_schema.file_summary_by_event_name\G
  2. ...
  3. *************************** 2. row ***************************
  4.                EVENT_NAME: wait/io/file/sql/binlog
  5.                COUNT_STAR: 31
  6.            SUM_TIMER_WAIT: 8243784888
  7.            MIN_TIMER_WAIT: 0
  8.            AVG_TIMER_WAIT: 265928484
  9.            MAX_TIMER_WAIT: 6490658832
  10. ...
  11. mysql> SELECT * FROM performance_schema.file_summary_by_instance\G
  12. ...
  13. *************************** 2. row ***************************
  14.                 FILE_NAME: /var/mysql/share/english/errmsg.sys
  15.                EVENT_NAME: wait/io/file/sql/ERRMSG
  16.                EVENT_NAME: wait/io/file/sql/ERRMSG
  17.     OBJECT_INSTANCE_BEGIN: 4686193384
  18.                COUNT_STAR: 5
  19.            SUM_TIMER_WAIT: 13990154448
  20.            MIN_TIMER_WAIT: 26349624
  21.            AVG_TIMER_WAIT: 2798030607
  22.            MAX_TIMER_WAIT: 8150662536
  23. ...

Each file I/O 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:

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

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

Each file I/O summary table has the following summary columns containing aggregated values. Some columns are more general and have values that are the same as the sum of the values of more fine-grained columns. In this way, aggregations at higher levels are available directly without the need for user-defined views that sum lower-level columns.

  • COUNT_STAR, SUM_TIMER_WAIT, MIN_TIMER_WAIT, AVG_TIMER_WAIT, MAX_TIMER_WAIT

    These columns aggregate all I/O operations.

  • COUNT_READ, SUM_TIMER_READ, MIN_TIMER_READ, AVG_TIMER_READ, MAX_TIMER_READ, SUM_NUMBER_OF_BYTES_READ

    These columns aggregate all read operations, including FGETS, FGETC, FREAD, and READ.

  • COUNT_WRITE, SUM_TIMER_WRITE, MIN_TIMER_WRITE, AVG_TIMER_WRITE, MAX_TIMER_WRITE, SUM_NUMBER_OF_BYTES_WRITE

    These columns aggregate all write operations, including FPUTS, FPUTC, FPRINTF, VFPRINTF, FWRITE, and PWRITE.

  • COUNT_MISC, SUM_TIMER_MISC, MIN_TIMER_MISC, AVG_TIMER_MISC, MAX_TIMER_MISC

    These columns aggregate all other I/O operations, including CREATE, DELETE, OPEN, CLOSE, STREAM_OPEN, STREAM_CLOSE, SEEK, TELL, FLUSH, STAT, FSTAT, CHSIZE, RENAME, and SYNC. There are no byte counts for these operations.

The file I/O summary tables have these indexes:

TRUNCATE TABLE is permitted for file I/O summary tables. It resets the summary columns to zero rather than removing rows.

The MySQL server uses several techniques to avoid I/O operations by caching information read from files, so it is possible that statements you might expect to result in I/O events will not. You may be able to ensure that I/O does occur by flushing caches or restarting the server to reset its state.


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Document created the 26/06/2006, last modified the 26/10/2018
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References

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