show profile调优
有时候使用explain执行计划发现其实是命中了索引的，但是还是很慢，此时可以使用profile功能，show profile是mysql提供的可以用来分析当前会话中语句执行的资源消耗情况，如CPU、IO、IPC、SWAP以及发生的PAGE FAULTS等，可以用于SQL调优的测量
配置
默认情况下是关闭的
sql
mysql> show variables like '%profiling%';
+------------------------+-------+
| Variable_name | Value |
+------------------------+-------+
| have_profiling | YES |
| profiling | OFF |
| profiling_history_size | 15 |
+------------------------+-------+
have_profiling 表示当前mysql版本支持show profile功能
profiling 表示当前功能是否开启
profiling_history_size 表示可以保留的历史数量(sql条数)开启show profile
sql
set profiling = 1;查看
查看历史sql记录
sql
-- 由于上边的配置是15，所以最多显示最近15条记录
show profiles;根据query_id来分析该条sql的性能问题
sql
show profile cpu,block io for query 18;
+----------------------+----------+----------+------------+--------------+---------------+
| Status | Duration | CPU_user | CPU_system | Block_ops_in | Block_ops_out |
+----------------------+----------+----------+------------+--------------+---------------+
| starting | 0.000084 | 0.000067 | 0.000013 | 0 | 0 |
| checking permissions | 0.000014 | 0.000008 | 0.000005 | 0 | 0 |
| Opening tables | 0.000039 | 0.000036 | 0.000003 | 0 | 0 |
| init | 0.000017 | 0.000015 | 0.000002 | 0 | 0 |
| System lock | 0.000009 | 0.000008 | 0.000001 | 0 | 0 |
| optimizing | 0.000004 | 0.000003 | 0.000001 | 0 | 0 |
| statistics | 0.000011 | 0.000010 | 0.000001 | 0 | 0 |
| preparing | 0.000009 | 0.000008 | 0.000001 | 0 | 0 |
| executing | 0.000003 | 0.000002 | 0.000001 | 0 | 0 |
| Sending data | 0.000039 | 0.000037 | 0.000001 | 0 | 0 |
| end | 0.000004 | 0.000003 | 0.000002 | 0 | 0 |
| query end | 0.000007 | 0.000006 | 0.000001 | 0 | 0 |
| closing tables | 0.000008 | 0.000007 | 0.000001 | 0 | 0 |
| freeing items | 0.000016 | 0.000007 | 0.000009 | 0 | 0 |
| cleaning up | 0.000015 | 0.000013 | 0.000001 | 0 | 0 |
+----------------------+----------+----------+------------+--------------+---------------+该查询展示出了这条sql完整的执行生命周期
可以查询的类型有
- all 显示所有开销
- block io 显示块io开销
- cpu 显示cpu开销
- context switches 上下文切换开销
- ipc 发送和接收相关开销
- memory 内存开销
- page faults 页面错误相关开销
- source 显示Source_function、Source_file、Source_line相关开销
- swaps 交换次数相关开销
PROFILING表
除了使用show profiles;来查询之外，还可以使用information_schema.PROFILING表来进行查询，且可以进行排序等操作
sql
select state,sum(duration) as total_r,
round(100*sum(duration)/ (select sum(duration) from information_schema.PROFILING where query_id = 71),2) as pct_r,
count(*) as calls
from information_schema.PROFILING
where query_id = 71
group by state
order by total_r desc如何判断哪些是出现问题的？
如果在执行过程中存在以下情况，则需要进行优化
- converting HEAP to MyISAM 查询结果太大，内存不够用了，开始使用磁盘
- create tmp table 创建临时表
- Copying to tmp table on disk 将内存中的临时表复制到磁盘
- locked
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