show databases;
Database
information_schema
mtr
mysql
performance_schema
test
select count(*) from performance_schema.performance_timers;
count(*)
5
select count(*) from performance_schema.setup_consumers;
count(*)
12
select count(*) > 3 from performance_schema.setup_instruments;
count(*) > 3
1
select count(*) from performance_schema.setup_timers;
count(*)
4
show engine PERFORMANCE_SCHEMA status;
show status like "performance_schema%";
show variables like "performance_schema_users_size";
Variable_name	Value
performance_schema_users_size	0
select count(*) from performance_schema.users;
count(*)
0
select variable_value > 0 from information_schema.global_status
where variable_name like 'PERFORMANCE_SCHEMA_USERS_LOST';
variable_value > 0
1