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记录mysql性能查询过程

2012-10-10 10:09  轩脉刃  阅读(6203)  评论(3编辑  收藏  举报

一切源于一个实验,请看下面的例子:

表:

CREATE TABLE IF NOT EXISTS `foo` (
`a` int(10) unsigned NOT NULL AUTO_INCREMENT,
`b` int(10) unsigned NOT NULL,
`c` varchar(100) NOT NULL,
PRIMARY KEY (`a`),
KEY `bar` (`b`,`a`)
) ENGINE=InnoDB;

CREATE TABLE IF NOT EXISTS `foo2` (
`a` int(10) unsigned NOT NULL AUTO_INCREMENT,
`b` int(10) unsigned NOT NULL,
`c` varchar(100) NOT NULL,
PRIMARY KEY (`a`),
KEY `bar` (`b`,`a`)

) ENGINE=MyISAM;

我往两个表中插入了30w的数据(插入的时候性能差别InnoDB比MyISAM慢)

<?php

$host = '192.168.100.166';

$dbName = 'test';

$user = 'root';

$password = '';

$db = mysql_connect($host, $user, $password) or die('DB connect failed');

mysql_select_db($dbName, $db);

echo '===================InnoDB=======================' . "\r\n";

$start = microtime(true);

mysql_query("SELECT SQL_NO_CACHE SQL_CALC_FOUND_ROWS * FROM foo WHERE b = 1 LIMIT 1000, 10");

$end = microtime(true);

echo $end - $start . "\r\n";

echo '===================MyISAM=======================' . "\r\n";

$start = microtime(true);

mysql_query("SELECT SQL_NO_CACHE SQL_CALC_FOUND_ROWS * FROM foo2 WHERE b = 1 LIMIT 1000, 10");

$end = microtime(true);

echo $end - $start . "\r\n";

返回结果:

clip_image001

一次查询就会差别这么多!!InnoDB和MyISAM,赶紧分析分析为什么。

首先是使用explain来进行查看

clip_image002

确定两边都没有使用index,第二个查询查的rows,并且MyISAM的查询rows还比InnoDB少这么多,反而是查询慢于InnoDB!!这Y的有点奇怪。

 

没事,还有一个牛掰工具profile

具体使用可以参考:http://dev.mysql.com/doc/refman/5.0/en/show-profile.html

使用方法简单来说:

Mysql > set profiling = 1;

Mysql>show profiles;

Mysql>show profile for query 1;

clip_image003

 

这个数据中就可以看到MyISAM的Sending data比InnoDB的Sending data费时太多了。查看mysql文档

http://dev.mysql.com/doc/refman/5.0/en/general-thread-states.html

 

Sending data

The thread is reading and processing rows for a SELECT statement, and sending data to the client. Because operations occurring during this this state tend to perform large amounts of disk access (reads), it is often the longest-running state over the lifetime of a given query.

 

Sending data是去磁盘中读取select的结果,然后将结果返回给客户端。这个过程会有大量的IO操作。你可以使用show profile cpu for query XX;来进行查看,发现MyISAM的CPU_system比InnnoDB大很多。至此可以得出结论是MyISAM进行表查询(区别仅仅使用索引就可以完成的查询)比InnoDB慢。

 

至于再往下的为什么,我想就需要看源码了..于是,就此打住。

 

附带一篇文章,里面还有status的用法

http://hi.baidu.com/thinkinginlamp/item/8d038333c6b0674a3075a1d3

 

参考文章:

http://dev.mysql.com/doc/refman/5.0/en/show-profile.html

http://stackoverflow.com/questions/6274891/mysql-innodb-count-vs-counting-rows-on-server-side

http://www.yqshare.com/mysql-sql-show-profile.html

http://stackoverflow.com/questions/3638624/mysql-profiler-sending-data

http://hi.baidu.com/hexie007/item/126939785b86353c714423cd

http://moonbingbing.blogspot.com/2010/12/mysql-profilesending-data.html