Spec-Zone .ru
спецификации, руководства, описания, API
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Spec-Zone .ru
спецификации, руководства, описания, API
|
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 contain NULL indicate which timers
you can use in setup_timers.
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.