MySQL调优利器【show profiles】
show profiles
是mysql提供可用来分析当前会话中语句执行的资源消耗情况，可以用于SQL的调优测量。
默认情况下，参数处于关闭状态，并保存最近15次的运行结果
分析步骤
1、查看当前版本sql是否支持show profiles
mysql> show variables like 'profiling%';
+------------------------+-------+
| Variable_name | Value |
+------------------------+-------+
| profiling | OFF |
| profiling_history_size | 15 |
+------------------------+-------+
2、开启该功能
mysql> set global profiling=ON;
Query OK, 0 rows affected, 1 warning (0.00 sec)
之后重新连接mysql或新建会话生效。
3、随便执行下sql
## sql语句本身没太大含义 只是为了演示
select * from emp group by id limit 150000;
select * from emp group by id order by 5;
4、查看结果show profiles
mysql> show profiles;
+----------+------------+-------------------------------------------------------------+
| Query_ID | Duration | Query |
+----------+------------+-------------------------------------------------------------+
| 1 | 0.00492775 | select @@version_comment limit 1 |
| 2 | 0.00012475 | ues bigdata |
| 3 | 0.00019650 | SELECT DATABASE() |
| 4 | 0.00989825 | show databases |
| 5 | 0.00027950 | show tables |
| 6 | 0.00820250 | show variables like 'profiling%' |
| 7 | 0.00034350 | select * from emp group by id%10 limit 150000 |
| 8 | 0.00031925 | select id,empno,ename from emp group by id%10 limit 150000 |
| 9 | 0.13237350 | select id,empno,ename from emp group by id limit 150000 |
| 10 | 0.00033525 | select id,empno,ename from emp group by id limit 5 |
+----------+------------+-------------------------------------------------------------+
10 rows in set, 1 warning (0.00 sec)
5、诊断sql
show profile 参数 for query x(x表示show Profiles得到的query_id)
参数介绍:
1、ALL 显示所有的开销信息
2、BLOCK IO 显示块IO相关开销
3、CONTEXT SWITCHES 上下文切换相关开销
4、CPU 显示CPU相关开销信息
5、IPC 显示发送和接收相关开销信息
6、MEMORY 显示内存相关开销信息
7、PAGE FAULTS 显示页面错误相关开销信息
8、SOURCE 显示和Source_function、Source_file、Source_line相关的开销信息
9、SWAPS 显示交换次数相关开销的信息
举例：诊断Query_ID=9的SQL
show profile all for query 9;
mysql> show profile cpu,block io for query 9;
+----------------------+----------+----------+------------+--------------+---------------+
| Status | Duration | CPU_user | CPU_system | Block_ops_in | Block_ops_out |
+----------------------+----------+----------+------------+--------------+---------------+
| starting | 0.000084 | 0.000054 | 0.000009 | 0 | 0 |
| checking permissions | 0.000007 | 0.000005 | 0.000001 | 0 | 0 |
| Opening tables | 0.000016 | 0.000014 | 0.000002 | 0 | 0 |
| init | 0.000020 | 0.000018 | 0.000003 | 0 | 0 |
| System lock | 0.000009 | 0.000007 | 0.000001 | 0 | 0 |
| optimizing | 0.000004 | 0.000004 | 0.000001 | 0 | 0 |
| statistics | 0.000030 | 0.000025 | 0.000004 | 0 | 0 |
| preparing | 0.000014 | 0.000012 | 0.000002 | 0 | 0 |
| Sorting result | 0.000004 | 0.000003 | 0.000000 | 0 | 0 |
| executing | 0.000002 | 0.000002 | 0.000001 | 0 | 0 |
| Sending data | 0.132000 | 0.004110 | 0.127747 | 0 | 0 |
| end | 0.000018 | 0.000009 | 0.000001 | 0 | 0 |
| query end | 0.000011 | 0.000009 | 0.000002 | 0 | 0 |
| closing tables | 0.000011 | 0.000009 | 0.000002 | 0 | 0 |
| freeing items | 0.000129 | 0.000000 | 0.000129 | 0 | 0 |
| cleaning up | 0.000016 | 0.000000 | 0.000015 | 0 | 0 |
+----------------------+----------+----------+------------+--------------+---------------+
16 rows in set, 1 warning (0.00 sec)
其中status表示sql执行生命周期，Duration表示该步骤的耗时
可以看出Sending data耗时较大。
注意:如果status中出现了以下内容，说明sql出现了性能问题
1、converting heap to MyISAM 查询结果太大，内存都不够用了 往磁盘上放
2、Creating tmp table 创建临时表，用完再删(group by 有时也会创建临时表)
3、copying to tmp table on disk 把内存中临时表复制到磁盘
4、locked 表被锁了