MySQL 5.6 Reference Manual Including MySQL NDB Cluster 7.3-7.4 Reference Guide
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 |
| TICK | 105 | 1 | 2416 |
+-------------+-----------------+------------------+----------------+
If the values associated with a given timer name are
NULL, that timer is not supported on your
platform. The rows that do not contain NULL
indicate which timers you can use in
setup_timers. For an explanation
of how event timing occurs, see
Section 22.4.1, “Performance Schema Event Timing”.
The performance_timers table has
these columns:
TIMER_NAME
The name by which to refer to the timer when configuring
the setup_timers table.
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.
TRUNCATE TABLE is not permitted
for the performance_timers table.