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20.7.6. Performance Schema Miscellaneous Tables

The PERFORMANCE_TIMERS table shows which event timers are available: 

mysql> SELECT * FROM PERFORMANCE_TIMERS;
+-------------+-----------------+------------------+----------------+
| TIMER_NAME  | TIMER_FREQUENCY | TIMER_RESOLUTION | TIMER_OVERHEAD |
+-------------+-----------------+------------------+----------------+
| CYCLE       |      2389029850 |                1 |             72 |
| NANOSECOND  |            NULL |             NULL |           NULL |
| MICROSECOND |         1000000 |                1 |            585 |
| MILLISECOND |            1035 |                1 |            738 |
| TICK        |             101 |                1 |            630 |
+-------------+-----------------+------------------+----------------+

If the values associated with a given timer name are NULL, that timer is not supported on your platform. The rows that do not have NULL indicate which timers you can use.

The PERFORMANCE_TIMERS table has these columns:

  • TIMER_NAME

    The name by which to refer to the timer.

  • TIMER_FREQUENCY

    The number of timer units per second. For a cycle timer, the frequency is generally related to the CPU speed. The CYCLE value of 2388761194 was obtained on a system with a 2.4GHz processor.

  • TIMER_RESOLUTION

    Indicates the number of timer units by which timer values increase at a time. If a timer has a resolution of 10, its value increases by 10 each time.

  • TIMER_OVERHEAD

    The minimal number of cycles of overhead to obtain one timing with the given timer. Performance Schema determines this value by invoking the timer 20 times during initialization and picking the smallest value. The total overhead really is twice this because the instrumentation invokes the timer at the start and end of each event. The timer code is called only for timed events, so this overhead does not apply for nontimed events.

The PROCESSLIST table has these columns:

  • THREAD_ID

    This is the unique identifier of an instrumented thread.

  • ID

    For threads that are displayed in INFORMATION_SCHEMA.PROCESSLIST, this is the INFORMATION_SCHEMA.ID value. ID is not unique, and is 0 for threads not associated with a user connection, such as server internal background threads.

  • NAME

    NAME is the name associated with the instrumentation of the code in the server. For example, thread/sql/one_connection corresponds to the thread function in the code responsible for handling a user connection.