高性能MySQL（三）：服务器性能剖析

select * from c LEFT JOIN c100w on c.id=c100w.id;  -- 联合查询
show PROFILES;  -- 查看查询耗时
select * from c;
show PROFILE for  query 1 ;

set @query_id=282;
select state,sum(DURATION) as total_r,
ROUND(100*sum(duration)/(select sum(duration) from information_schema.PROFILING
where QUERY_ID=@query_id),2) as pct_r,
count(*) as calls,
sum(duration)/count(*) as "r/call"
from information_schema.PROFILING
where QUERY_ID=@query_id
GROUP BY STATE
order by total_r desc

查询优化

select * from c LEFT JOIN c100w on c.id=c100w.id;  -- 联合查询
show PROFILES;  -- 查看查询耗时

select * from c;
show PROFILE for  query 1 ;

set @query_id=282;
select state,sum(DURATION) as total_r,
ROUND(100*sum(duration)/(select sum(duration) from information_schema.PROFILING
where QUERY_ID=@query_id),2) as pct_r,
count(*) as calls,
sum(duration)/count(*) as "r/call"
from information_schema.PROFILING
where QUERY_ID=@query_id
GROUP BY STATE
order by total_r desc

show profile

flush status;  -- 清除表缓存
show STATUS where variable_name like 'Handler%' or variable_name like 'Created%'  -- 计数器

select event_name,count_star,sum_timer_wait
from `performance_schema`.events_waits_summary_global_by_event_name
order by sum_timer_wait desc LIMIT 5