分析SQL执行带来的开销是优化SQL的常用手段，在MySQL数据库中，可以通过配置profiling参数来启用SQL剖析。
它只能在session级别来设置，设置后影响当前session；当它开启后，后续执行的SQL语句都将记录其资源开销，诸如IO，上下文，CPU，MEMORY等。

实验环境：

mysql> select version();

+------------+

| version() |

+------------+

| 5.7.17-log |

+------------+

1 row in set (0.00 sec)

与profile相关的三个参数：

mysql> show variables like '%profil%';

+------------------------+-------+

| Variable_name | Value |

+------------------------+-------+

| have_profiling | YES | ---用于控制是否由系统变量开启或禁用profiling

| profiling | OFF |---开启SQL语句剖析功能

| profiling_history_size | 15 |---设置保留profiling的数目，缺省为15，范围为0至100，为0时将禁用profiling

+------------------------+-------+

3 rows in set (0.01 sec)

开启profiling,有个警告，这个参数在以后会被删除，用information_scheam.PROFILING替代。

mysql> set profiling=1;

Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> show warnings;
+---------+------+----------------------------------------------------------------------+
| Level| Code | Message |
+---------+------+----------------------------------------------------------------------+
| Warning | 1287 | '@@profiling' is deprecated and will be removed in a future release. |
+---------+------+----------------------------------------------------------------------+

执行一条sql测试一下:

select * from oms3.customers where `type` = 1 AND `status` < 7 AND `isarea` = 6 AND `into_time`>='2016-12-01'AND `into_time`<='2017-01-02 23:59:59' order by score desc limit 40,20

sql执行很慢，执行完成之后查看:

mysql> show profiles;

+----------+--------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

| Query_ID | Duration | Query |

+----------+--------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

| 7 | 0.00022275 | SELECT * FROM setup_actors |

| 8 | 0.00016050 | SELECT DATABASE() |

| 9 | 0.00032350 | show databases |

| 10 | 0.00024050 | show tables |

| 11 | 0.00019250 | SELECT * FROM setup_actors |

| 12 | 0.00183950 | show variables like "profiling_hist%" |

| 13 | 0.00192500 | show variables like '%profil%' |

| 14 | 0.00011550 | show warnings |

| 15 | 0.00044725 | help 'show profile' |

| 16 | 0.00013875 | set profiling=1 |

| 17 | 0.00011550 | show warnings |

| 18 | 0.00025075 | select * from customers where `type` = 1 AND `status` < 7 AND `isarea` = 6 AND `into_time`>='2016-12-01'AND `into_time`<='2017-01-02 23:59:59' order by score desc limit 40,20 |

| 19 | 333.19133875 | select * from oms3.customers where `type` = 1 AND `status` < 7 AND `isarea` = 6 AND `into_time`>='2016-12-01'AND `into_time`<='2017-01-02 23:59:59' order by score desc limit 40,20 |

| 20 | 0.00011250 | show profilings |

| 21 | 0.00010975 | show profilings |

+----------+--------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

15 rows in set, 1 warning (0.00 sec)

mysql> set @query_id=19;---上面显示是query_id为19

Query OK, 0 rows affected (0.00 sec)

mysql> select STATE,sum(duration) as Total_R, ---用这条sql查询具体是哪里出问题，这条sql引用于《High Performance MySQL,Third Edition》

-> 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;

+----------------------+------------+-------+-------+----------------+

| STATE | Total_R | Pct_R | calls | R/Call |

+----------------------+------------+-------+-------+----------------+

| Sending data | 332.162424 | 99.69 | 1 | 332.1624240000 | ---这个state基本占用了全部的资源，那么对这条sql的优化就着重于减少io上。

| statistics | 1.027729 | 0.31 | 1 | 1.0277290000 |

| Opening tables | 0.000519 | 0.00 | 1 | 0.0005190000 |

| freeing items | 0.000157 | 0.00 | 1 | 0.0001570000 |

| starting | 0.000147 | 0.00 | 1 | 0.0001470000 |

| init | 0.000123 | 0.00 | 1 | 0.0001230000 |

| logging slow query | 0.000096 | 0.00 | 1 | 0.0000960000 |

| preparing | 0.000035 | 0.00 | 1 | 0.0000350000 |

| cleaning up | 0.000019 | 0.00 | 1 | 0.0000190000 |

| optimizing | 0.000016 | 0.00 | 1 | 0.0000160000 |

| end | 0.000014 | 0.00 | 1 | 0.0000140000 |

| System lock | 0.000014 | 0.00 | 1 | 0.0000140000 |

| closing tables | 0.000013 | 0.00 | 1 | 0.0000130000 |

| query end | 0.000013 | 0.00 | 1 | 0.0000130000 |

| Sorting result | 0.000010 | 0.00 | 1 | 0.0000100000 |

| checking permissions | 0.000009 | 0.00 | 1 | 0.0000090000 |

| executing | 0.000003 | 0.00 | 1 | 0.0000030000 |

+----------------------+------------+-------+-------+----------------+

17 rows in set, 18 warnings (0.00 sec)

其他用法：

mysql> SHOW PROFILE CPU FOR QUERY 2;

+----------------------+----------+----------+------------+

| Status | Duration | CPU_user | CPU_system |

+----------------------+----------+----------+------------+

| checking permissions | 0.000040 | 0.000038 | 0.000002 |

| creating table | 0.000056 | 0.000028 | 0.000028 |

| After create | 0.011363 | 0.000217 | 0.001571 |

| query end | 0.000375 | 0.000013 | 0.000028 |

| freeing items | 0.000089 | 0.000010 | 0.000014 |

| logging slow query | 0.000019 | 0.000009 | 0.000010 |

| cleaning up | 0.000005 | 0.000003 | 0.000002 |

+----------------------+----------+----------+------------+

更多用法详见：

help show profiles;