mysql的sql性能分析器

author：skate
time：2012/02/17
 
mysql的sql性能分析器
 
MySQL 的SQL性能分析器主要用途是显示SQL执行的整个过程中各项资源的使用情况。分析器可以更好的展示
出不良SQL的性能问题所在。
 
mysql sql profile的使用方法
 
1.开启mysql sql profile
 
检查mysql sql profile是否启用
mysql> select @@profiling;
+-------------+
| @@profiling |
+-------------+
|           0 |
+-------------+
1 row in set (0.01 sec)
 
默认情况下profiling 的值为0表示MySQL SQL Profiler处于OFF状态，如果开启SQL性能分析器后，profiling 的值将为1.
 
mysql> set profiling=1;
Query OK, 0 rows affected (0.03 sec)
 
mysql> select @@profiling;
+-------------+
| @@profiling |
+-------------+
|           1 |
+-------------+
1 row in set (0.01 sec)
 
 
上面可以看到profiling已经变为1了，但是这个是session级别的，系统是不支持的。如下测试
 
退出mysql
mysql> quit
Bye
[root@localhost ~]# mysql -uroot -p
Enter password:
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 3
Server version: 5.0.45-log Source distribution
 
Type 'help;' or '\h' for help. Type '\c' to clear the buffer.
 
查看profiling的值
mysql> select @@profiling;
+-------------+
| @@profiling |
+-------------+
|           0 |
+-------------+
1 row in set (0.01 sec)
 
发现已经变为默认值0了，那如果设置系统级会如何呢？
 
mysql> set global profiling=1;
ERROR 1228 (HY000): Variable 'profiling' is a SESSION variable and can't be used with SET GLOBAL
mysql>
 
看到这里报错了。所以mysql sql profile是session级别的。
 
2. 举个例如，看如何使用
 
mysql> create table t5 as select * from t1;
ERROR 1046 (3D000): No database selected
mysql> use backup;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A
 
Database changed
mysql> create table t5 as select * from t1;
Query OK, 2 rows affected (0.06 sec)
Records: 2  Duplicates: 0  Warnings: 0
 
mysql> select count(*) from t5;
+----------+
| count(*) |
+----------+
|        2 |
+----------+
1 row in set (0.00 sec)
 
mysql> select count(*) from t5;
+----------+
| count(*) |
+----------+
|        2 |
+----------+
1 row in set (0.00 sec)