查看mysql语句运行时间的2种方法
作者:
网站运行很慢的时候,我就特别起知道为什么这么慢,所以我查啊查,数据库绝对是很重要的一部分,里面运行的sql是绝对不能放过的。平时做项目的时候,我也会注意sql语句的书写,写出一些高效的sql来,所以我会经常测试自己写的sql语句。我把我知道的二个方法,总结一下发出来
网站运行很慢的时候,我就特别起知道为什么这么慢,所以我查啊查,数据库绝对是很重要的一部分,里面运行的sql是绝对不能放过的。平时做项目的时候,我也会注意sql语句的书写,写出一些高效的sql来,所以我会经常测试自己写的sql语句。我把我知道的二个方法,总结一下发出来。
一,show profiles 之类的语句来查看
1,查一下profile是不是打开了,默认是不打开的。
mysql> show profiles; Empty set (0.02 sec) mysql> show variables like "%pro%"; +---------------------------+-------+ | Variable_name | Value | +---------------------------+-------+ | profiling | OFF | | profiling_history_size | 15 | | protocol_version | 10 | | slave_compressed_protocol | OFF | +---------------------------+-------+ 4 rows in set (0.00 sec)
我查看一下profiles里面没有东西,所以公司的电脑里面profile是没有打开的,我查看了一下mysql变量,果然是OFF的。
2,开启profile,然后测试
开启profile
mysql> set profiling=1; Query OK, 0 rows affected (0.00 sec)
测试如下:
mysql> show tables; +----------------+ | Tables_in_test | +----------------+ | aa | | bb | | comment | | string_test | | user | +----------------+ 5 rows in set (0.00 sec) mysql> select * from aa; +----+------+------------+------+ | id | name | nname | sex | +----+------+------------+------+ | 2 | tank | bbbb,4bbbb | NULL | | 3 | zhang| 3,c,u | NULL | +----+------+------------+------+ 2 rows in set (0.00 sec) mysql> update aa set name='d'; Query OK, 2 rows affected (0.00 sec) Rows matched: 2 Changed: 2 Warnings: 0 mysql> delete from bb; Query OK, 2 rows affected (0.00 sec) mysql> show profiles; +----------+------------+------------------------+ | Query_ID | Duration | Query | +----------+------------+------------------------+ | 1 | 0.00054775 | show tables | | 2 | 0.00022400 | select * from aa | | 3 | 0.00026275 | update aa set name='d' | | 4 | 0.00043000 | delete from bb | +----------+------------+------------------------+ 4 rows in set (0.00 sec) mysql> show profile; +----------------------+-----------+ | Status | Duration | +----------------------+-----------+ | (initialization) | 0.0000247 | | checking permissions | 0.0000077 | | Opening tables | 0.0000099 | | System lock | 0.000004 | | Table lock | 0.000005 | | init | 0.0003057 | | query end | 0.0000062 | | freeing items | 0.000057 | | closing tables | 0.000008 | | logging slow query | 0.0000015 | +----------------------+-----------+ 10 rows in set (0.00 sec) mysql> show profile for query 1; +----------------------+-----------+ | Status | Duration | +----------------------+-----------+ | (initialization) | 0.000028 | | checking permissions | 0.000007 | | Opening tables | 0.0000939 | | System lock | 0.0000017 | | Table lock | 0.0000055 | | init | 0.000009 | | optimizing | 0.0000027 | | statistics | 0.0000085 | | preparing | 0.0000065 | | executing | 0.000004 | | checking permissions | 0.000258 | | Sending data | 0.000049 | | end | 0.0000037 | | query end | 0.0000027 | | freeing items | 0.0000307 | | closing tables | 0.0000032 | | removing tmp table | 0.0000275 | | closing tables | 0.0000037 | | logging slow query | 0.000002 | +----------------------+-----------+ 19 rows in set (0.00 sec) mysql> show profile for query 3; +----------------------+-----------+ | Status | Duration | +----------------------+-----------+ | (initialization) | 0.0000475 | | checking permissions | 0.0000077 | | Opening tables | 0.000026 | | System lock | 0.0000042 | | Table lock | 0.0000045 | | init | 0.0000205 | | Updating | 0.0000787 | | end | 0.0000567 | | query end | 0.000004 | | freeing items | 0.0000067 | | closing tables | 0.000004 | | logging slow query | 0.000002 | +----------------------+-----------+ 12 rows in set (0.00 sec)
二,timestampdiff来查看测试时间
mysql> set @d=now(); Query OK, 0 rows affected (0.00 sec) mysql> select * from comment; +------+-----+------+------------+---------------------+ | c_id | mid | name | content | datetime | +------+-----+------+------------+---------------------+ | 1 | 1 | ?? | 2222222211 | 2010-05-12 00:00:00 | | 2 | 1 | ?? | ????(??) | 2010-05-13 00:00:00 | | 3 | 2 | tank | ?????? | 0000-00-00 00:00:00 | +------+-----+------+------------+---------------------+ 3 rows in set (0.00 sec) mysql> select timestampdiff(second,@d,now()); +--------------------------------+ | timestampdiff(second,@d,now()) | +--------------------------------+ | 0 | +--------------------------------+ 1 row in set (0.00 sec)
这种方法有一点要注意,就是三条sql语句要尽量连一起执行,不然误差太大,根本不准
set @d=now(); select * from comment; select timestampdiff(second,@d,now());
如果是用命令行来执行的话,有一点要注意,就是在select timestampdiff(second,@d,now());后面,一定要多copy一个空行,不然最后一个sql要你自己按回车执行,这样就不准了。
其实我觉得吧,真正要我们关心的是那些查询慢的sql,因为真正影响速度的是他们,关于慢查询的东西,有空写一下。