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26.12.18.4 The performance_timers Table

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The performance_timers table shows which event timers are available:

  1. mysql> SELECT * FROM performance_schema.performance_timers;
  2. +-------------+-----------------+------------------+----------------+
  3. | TIMER_NAME  | TIMER_FREQUENCY | TIMER_RESOLUTION | TIMER_OVERHEAD |
  4. +-------------+-----------------+------------------+----------------+
  5. | CYCLE       |      2389029850 |                1 |             72 |
  6. | NANOSECOND  |      1000000000 |                1 |            112 |
  7. | MICROSECOND |         1000000 |                1 |            136 |
  8. | MILLISECOND |            1036 |                1 |            168 |
  9. +-------------+-----------------+------------------+----------------+

If the values associated with a given timer name are NULL, that timer is not supported on your platform. For an explanation of how event timing occurs, see Section 26.4.1, “Performance Schema Event Timing”.

The performance_timers table has these columns:

  • TIMER_NAME

    The timer name.

  • TIMER_FREQUENCY

    The number of timer units per second. For a cycle timer, the frequency is generally related to the CPU speed. For example, on a system with a 2.4GHz processor, the CYCLE may be close to 2400000000.

  • TIMER_RESOLUTION

    Indicates the number of timer units by which timer values increase. 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. The 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 amount 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 performance_timers table has these indexes:

  • None

TRUNCATE TABLE is not permitted for the performance_timers table.


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