分析mysql中sql语句的性能，可以使用show profiles查询语句，查看是否打开了profiles功能，根据query_id 查看某个查询的详细时间耗费等。
Show profiles是5.0.37之后添加的。
查看数据库版本：
复制代码 代码示例:
mysql> Select version();
+---------------------+
| version() |
+---------------------+
| 5.0.82-community-nt |
+---------------------+
1 row in set (0.00 sec)
版本是支持show profiles功能的。
开始进入mysql性能跟踪诊断过程。
查看是否打开了profiles功能，默认关闭：
复制代码 代码示例:
mysql> use test;
Database changed
mysql> show profiles;
Empty set (0.00 sec)
显示为空，说明profiles功能是关闭，开启profiles：
复制代码 代码示例:
mysql> set profiling=1;
Query OK, 0 rows affected (0.00 sec)
执行查询：
复制代码 代码示例:
mysql> explain select distinct player_idfrom task limit 20;
mysql> select distinct player_id from task ;
然后，执行 show profiles
复制代码 代码示例:
mysql> show profiles;
+----------+------------+------------------------------------------------------+
| Query_ID | Duration | Query |
+----------+------------+------------------------------------------------------+
| 1 | 0.00035225 | explain select distinct player_id from task limit 20 |
| 2 | 1.91772775 | select distinct player_id from task |
+----------+------------+------------------------------------------------------+
此时可以看到执行select distinct player_id from task 用了1.91772775秒的时间
根据query_id 查看某个查询的详细时间耗费
复制代码 代码示例:
mysql> show profile for query 2;
+----------------------+----------+
| Status | Duration |
+----------------------+----------+
| starting | 0.000052 |
| Opening tables | 0.000009 |
| System lock | 0.000003 |
| Table lock | 0.000007 |
| init | 0.000013 |
| optimizing | 0.000003 |
| statistics | 0.000009 |
| preparing | 0.000008 |
| Creating tmp table | 0.000074 |
| executing | 0.000002 |
| Copying to tmp table |1.916551 |
| Sending data | 0.000667 |
| end | 0.000004 |
| removing tmp table | 0.000065 |
| end | 0.000002 |
| end | 0.000002 |
| query end | 0.000003 |
| freeing items | 0.000245 |
| closing tables | 0.000006 |
| logging slow query | 0.000002 |
| cleaning up | 0.000003 |
+----------------------+----------+
可以看到红色字体部分耗费了大量时间，这是因为distinct查看会用到临时表。
查看占用cpu、 io等信息：
复制代码 代码示例:
mysql> show profile block io,cpu for query2;
+----------------------+----------+----------+------------+--------------+------
---------+
| Status | Duration | CPU_user |CPU_system | Block_ops_in | Block
_ops_out |
+----------------------+----------+----------+------------+--------------+------
---------+
| starting | 0.000052 | NULL | NULL | NULL |
NULL |
| Opening tables | 0.000009 | NULL | NULL | NULL |
NULL |
| System lock | 0.000003 | NULL | NULL | NULL |
NULL |
| Table lock | 0.000007 | NULL | NULL | NULL |
NULL |
| init | 0.000013 | NULL | NULL | NULL |
NULL |
| optimizing | 0.000003 | NULL | NULL | NULL |
NULL |
| statistics | 0.000009 | NULL | NULL | NULL |
NULL |
| preparing | 0.000008 | NULL | NULL | NULL |
NULL |
| Creating tmp table | 0.000074 | NULL | NULL | NULL |
NULL |
| executing | 0.000002 | NULL | NULL | NULL |
NULL |
| Copying to tmp table | 1.916551 | NULL | NULL | NULL |
NULL |
| Sending data | 0.000667 | NULL | NULL | NULL |
NULL |
| end | 0.000004 | NULL | NULL | NULL |
NULL |
| removing tmp table | 0.000065 | NULL | NULL | NULL |
NULL |
| end | 0.000002 | NULL | NULL | NULL |
NULL |
| end | 0.000002 | NULL | NULL | NULL |
NULL |
| query end | 0.000003 | NULL | NULL | NULL |
NULL |
| freeing items | 0.000245 | NULL | NULL | NULL |
NULL |
| closing tables | 0.000006 | NULL | NULL | NULL |
NULL |
| logging slow query | 0.000002 | NULL | NULL | NULL |
NULL |
| cleaning up | 0.000003 | NULL | NULL | NULL |
NULL |
+----------------------+----------+----------+------------+--------------+------
另外，可以看到memory,swaps,context switches,source等信息，show profiles输出的信息还是很丰富的。
参考：http://dev.mysql.com/doc/refman/5.0/en/show-profiles.html
