MySQL :: MySQL 8.4 Reference Manual :: 29.12.22.6 The performance_timers Table (original) (raw)

29.12.22.6 The performance_timers Table

The performance_timers table shows which event timers are available:

mysql> SELECT * FROM performance_schema.performance_timers;
+-------------+-----------------+------------------+----------------+
| TIMER_NAME  | TIMER_FREQUENCY | TIMER_RESOLUTION | TIMER_OVERHEAD |
+-------------+-----------------+------------------+----------------+
| CYCLE       |      2389029850 |                1 |             72 |
| NANOSECOND  |      1000000000 |                1 |            112 |
| MICROSECOND |         1000000 |                1 |            136 |
| MILLISECOND |            1036 |                1 |            168 |
| THREAD_CPU  |       339101694 |                1 |            798 |
+-------------+-----------------+------------------+----------------+

If the values associated with a given timer name areNULL, that timer is not supported on your platform. For an explanation of how event timing occurs, seeSection 29.4.1, “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, theCYCLE 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 no indexes.

TRUNCATE TABLE is not permitted for the performance_timers table.