查看mysql的执行计划
这条SQL执行4分钟，message_message有数据1000w，学写了下mysql的执行计划。
select * from message_message where id in(select message_id
from message_message_tags where messagetag_id=59885) and (category=9 or category=1)
order by sum(like_count,favorite_count) desc limit 15; www.2cto.com
在开发的过程中随着数据量的增大而感受到
数据库的性能比较差从而延伸到响应速度慢，
如果是开发人员很多时候估计是处于一种茫然状态，或者直接交给DBA去处理这问题，如果有DBA您很幸运，
但是如果没有DBA的前提下我们怎么去处理这问题，可能唯一的方法就是看执行计划
(也可以直接用explain SQL来分析...)：
默认情况下Mysql的profiling是关闭的，所以首先必须打开profiling
Sql代码
set profiling="ON"
mysql> show variables like "%profi%";
+------------------------+-------+
| Variable_name | Value |
+------------------------+-------+
| profiling | ON |
www.2cto.com
show processlist; 查看现在在运行的所有进程列表，在进程列表中我们唯一需要的是ID
mysql> show processlist;
+----+------+----------------+-----------+---------+------+-------+-------------
-----+
| Id | User | Host | db | Command | Time | State | Info
|
+----+------+----------------+-----------+---------+------+-------+-------------
-----+
| 3 | root | localhost:2196 | click_log | Query | 0 | NULL | show process
list |
+----+------+----------------+-----------+---------+------+-------+-------------
mysql> show profile cpu,memory for query 3;
+--------------------+------------+----------+------------+
| Status | Duration | CPU_user | CPU_system |
+--------------------+------------+----------+------------+
| freeing items | 0.00001375 | NULL | NULL |
| logging slow query | 0.00001375 | NULL | NULL |
| cleaning up | 0.00000050 | NULL | NULL |
+--------------------+------------+----------+------------+
SHOW PROFILES Syntax:
SHOW PROFILE [type [, type] ... ]
[FOR QUERY n] www.2cto.com
[LIMIT row_count [OFFSET offset]]
type:
ALL
| BLOCK IO
| CONTEXT SWITCHES
| CPU
| IPC
| MEMORY
| PAGE FAULTS
| SOURCE
| SWAPS
作者 san_yun