MySQL查询优化：profile功能，，这里还需要注意一点就是，需要安装profile模块才能实现。
1、不过版本要在5.0.37之后。(SHOW PROFILES and SHOW PROFILE were added in MySQL 5.0.37.)
SELECT @@profiling;
来查看是否已经启用profile，如果profilng值为0，可以通过
SET profiling = 1;
来启用。启用profiling之后，我们执行一条查询语句，比如：
select count(*) from roi_summary;
然后show profiles查看如下：
+—————-+————+———————————-+
| Query_ID | Duration | Query |
+—————-+————+———————————-+
| 1 | 0.00021500 | select @@profiling |
| 2 | 0.05522700 | select count(*) from roi_summary |
+—————-+————+———————————-+
2 rows in set (0.00 sec)
其中ID为5的语句是刚执行的查询语句
2、变量profiling是用户变量，每次都得重新启用。
以下是我做的一些实验。数据很明显，就不多解释了。
mysql> use test
Database changed
mysql> set profiling=1;
Query OK, 0 rows affected (0.00 sec)
mysql> show tables;
+—————-+
| Tables_in_test |
+—————-+
| bag_item |
| bag_user |
| score |
| t |
+—————-+
4 rows in set (0.03 sec)
mysql> select count(*) from t;
+———-+
| count(*) |
+———-+
| 2097152 |
+———-+
1 row in set (0.74 sec)
mysql> show profiles;
+———-+————+————————+
| Query_ID | Duration | Query |
+———-+————+————————+
| 1 | 0.02717000 | show tables |
| 2 | 0.74770100 | select count(*) from t |
+———-+————+————————+
2 rows in set (0.00 sec)
mysql> show profile for query 2;
+——————————–+———-+
| Status | Duration |
+——————————–+———-+
| (initialization) | 0.000004 |
| checking query cache for query | 0.000044 |
| Opening tables| 0.000012 |
| System lock | 0.000017 |
| Table lock | 0.00003 |
| init | 0.000013 |
| optimizing | 0.000008 |
| statistics | 0.000013 |
| preparing | 0.000011 |
| executing | 0.000006 |
| Sending data | 0.747313 |
| end | 0.000014 |
| query end | 0.000006 |
| storing result in query cache | 0.000006 |
| freeing items | 0.000012 |
| closing tables| 0.000009 |
| logging slow query | 0.000183 |
+——————————–+———-+
17 rows in set (0.00 sec)
mysql> show profile block io,cpu for query 2;
+——————————–+———-+———-+————+————–+—————+
| Status | Duration | CPU_user | CPU_system | Block_ops_in | Block_ops_out |
+——————————–+———-+———-+————+————–+—————+
| (initialization) | 0.000004 | 0 | 0 | 0 | 0 |
| checking query cache for query | 0.000044 | 0 | 0 | 0 | 0 |
| Opening tables| 0.000012 | 0 | 0 | 0 | 0 |
| System lock | 0.000017 | 0 | 0 | 0 | 0 |
| Table lock | 0.00003 | 0 | 0 | 0 | 0 |
| init | 0.000013 | 0 | 0 | 0 | 0 |
| optimizing | 0.000008 | 0 | 0 | 0 | 0 |
| statistics | 0.000013 | 0 | 0 | 0 | 0 |
| preparing | 0.000011 | 0 | 0 | 0 | 0 |
| executing | 0.000006 | 0 | 0 | 0 | 0 |
| Sending data | 0.747313 | 0.746887 | 0 | 0 | 0 |
| end | 0.000014 | 0 | 0 | 0 | 0 |
| query end | 0.000006 | 0 | 0 | 0 | 0 |
| storing result in query cache | 0.000006 | 0 | 0 | 0 | 0 |
| freeing items | 0.000012 | 0 | 0 | 0 | 0 |
| closing tables| 0.000009 | 0 | 0 | 0 | 0 |
| logging slow query | 0.000183 | 0 | 0 | 0 | 0 |
+——————————–+———-+———-+————+————–+—————+
17 rows in set (0.00 sec)
mysql> insert into t(username) select username from t;
Query OK, 2097152 rows affected (34.17 sec)
Records: 2097152 Duplicates: 0 Warnings: 0