MYSQL的profiling功能要在Mysql版本5.0.37以上才能使用。

查看profile是否开启

mysql> show variables like '%profil%';

+------------------------+-------+
| Variable_name     | Value |
+------------------------+-------+
| 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
+------------------------+-------+
2 rows in set (0.00 sec)

基于会话级别开启

mysql> set profiling = 1;     --关闭则用set profiling = off

Query OK, 0 rows affected (0.00 sec)

mysql> select distinct d.account,a.server_id from tab_appserver_user a
  -> inner join tab_department_parent b on a.key_id = b.parent_id
  -> inner join tab_department_member c on b.department_id = c.department_id and c.state=1
  -> and c.isdefault=1 inner join tab_user_info d on c.user_id = d.user_id and d.state=1
  -> where a.type=1 
  -> union          
  -> select distinct b.account,a.server_id from tab_appserver_user a
  -> inner join tab_user_info b on a.key_id = b.user_id and b.state=1
  -> where a.type=0;

查看是否设置生效：

select @@profiling;

默认是0，设置成功是1

运行SQL语句：

mysql> select * FROM hx_line WHERE id = '1455023';

查看profiles

mysql> show profiles;

+----------+------------+---------------------------------------------+
| Query_ID | Duration  | Query                    |
+----------+------------+---------------------------------------------+
|    1 | 0.00036150 | select * FROM hx_line WHERE id = '1455023' |
+----------+------------+---------------------------------------------+

查看具体某条的profile

mysql> show profile FOR QUERY 1;

+------------------------+-------+
| Variable_name     | Value |
+------------------------+-------+
| 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
+------------------------+-------+
2 rows in set (0.00 sec)

0

我们看到了一个简单的查询，MYSQL内部做了24次操作。
另外，看到了一堆query cache的操作，试着把query_cache_size=0，把query_cache关闭，再次测试：

mysql> show profile FOR QUERY 1;

+------------------------+-------+
| Variable_name     | Value |
+------------------------+-------+
| 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
+------------------------+-------+
2 rows in set (0.00 sec)

2

当开启了query_cache的情况下，需要多操作6次，在这个示例里面多化了0.000087s。

查询这条语句对CPU的使用情况：

+------------------------+-------+
| Variable_name     | Value |
+------------------------+-------+
| 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
+------------------------+-------+
2 rows in set (0.00 sec)

3

+------------------------+-------+
| Variable_name     | Value |
+------------------------+-------+
| 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
+------------------------+-------+
2 rows in set (0.00 sec)

4

查看io及cpu的消耗

+------------------------+-------+
| Variable_name     | Value |
+------------------------+-------+
| 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
+------------------------+-------+
2 rows in set (0.00 sec)

5

+------------------------+-------+
| Variable_name     | Value |
+------------------------+-------+
| 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
+------------------------+-------+
2 rows in set (0.00 sec)

6

使用查询语句对消耗进行排序

+------------------------+-------+
| Variable_name     | Value |
+------------------------+-------+
| 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
+------------------------+-------+
2 rows in set (0.00 sec)

7

+------------------------+-------+
| Variable_name     | Value |
+------------------------+-------+
| 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
+------------------------+-------+
2 rows in set (0.00 sec)

8

show profile额外一些命令：
* ALL - displays all information
* BLOCK IO - displays counts for block input and output Operations
* CONTEXT SWITCHES - displays counts for voluntary and involuntary context switches
* ipC - displays counts for messages sent and received
* MEMORY - is not currently implemented
* PAGE FAULTS - displays counts for major and minor page faults
* SOURCE - displays the names of functions from the source code, together with the name and line number of the file in which the function occurs
* SWAPS - displays swap counts

最后说明：profile是一个非常量化的子标，可以根据这些量化指标来比较各项资源的消耗，有利于我们对该语句的整体把控！