select * from performance_schema.performance_timers;
TIMER_NAME	TIMER_FREQUENCY	TIMER_RESOLUTION	TIMER_OVERHEAD
CYCLE	<frequency>	<resolution>	<overhead>
NANOSECOND	<frequency>	<resolution>	<overhead>
MICROSECOND	<frequency>	<resolution>	<overhead>
MILLISECOND	<frequency>	<resolution>	<overhead>
TICK	<frequency>	<resolution>	<overhead>
select * from performance_schema.performance_timers
where timer_name='CYCLE';
TIMER_NAME	TIMER_FREQUENCY	TIMER_RESOLUTION	TIMER_OVERHEAD
CYCLE	<frequency>	<resolution>	<overhead>
insert into performance_schema.performance_timers
set timer_name='FOO', timer_frequency=1,
timer_resolution=2, timer_overhead=3;
ERROR 42000: INSERT command denied to user 'root'@'localhost' for table 'performance_timers'
update performance_schema.performance_timers
set timer_frequency=12 where timer_name='CYCLE';
ERROR 42000: UPDATE command denied to user 'root'@'localhost' for table 'performance_timers'
delete from performance_schema.performance_timers;
ERROR 42000: DELETE command denied to user 'root'@'localhost' for table 'performance_timers'
delete from performance_schema.performance_timers
where timer_name='CYCLE';
ERROR 42000: DELETE command denied to user 'root'@'localhost' for table 'performance_timers'
LOCK TABLES performance_schema.performance_timers READ;
ERROR 42000: SELECT, LOCK TABLES command denied to user 'root'@'localhost' for table 'performance_timers'
UNLOCK TABLES;
LOCK TABLES performance_schema.performance_timers WRITE;
ERROR 42000: SELECT, LOCK TABLES command denied to user 'root'@'localhost' for table 'performance_timers'
UNLOCK TABLES;
#
# MDEV-25325 column_comment for performance_schema tables
#
select column_name, column_comment 
from information_schema.columns 
where table_schema='performance_schema' and table_name='performance_timers';
column_name	column_comment
TIMER_NAME	Time name, used in the setup_timers table.
TIMER_FREQUENCY	Number of timer units per second. Dependent on the processor speed.
TIMER_RESOLUTION	Number of timer units by which timed values increase each time.
TIMER_OVERHEAD	Minimum timer overhead, determined during initialization by calling the timer 20 times and selecting the smallest value. Total overhead will be at least double this, as the timer is called at the beginning and end of each timed event.