#### 27.12.21.4 The performance\_timers Table

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 The [`performance_timers`](performance-schema-performance-timers-table.html) 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 are `NULL`, that timer is not supported on your platform. For an explanation of how event timing occurs, see [Section 27.4.1, “Performance Schema Event Timing”](performance-schema-timing.html).

 The [`performance_timers`](performance-schema-performance-timers-table.html) 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`](performance-schema-performance-timers-table.html) table has no indexes.

[`TRUNCATE TABLE`](truncate-table.html) is not permitted for the [`performance_timers`](performance-schema-performance-timers-table.html) table.

