記錄mysql性能查詢過程


一切源於一個實驗,請看下面的例子:

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;

我往兩個表中插入了30w的數據(插入的時候性能差別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";

返回結果:

clip_image001

一次查詢就會差別這么多!!InnoDB和MyISAM,趕緊分析分析為什么。

首先是使用explain來進行查看

clip_image002

確定兩邊都沒有使用index,第二個查詢查的rows,並且MyISAM的查詢rows還比InnoDB少這么多,反而是查詢慢於InnoDB!!這Y的有點奇怪。

 

沒事,還有一個牛掰工具profile

具體使用可以參考:http://dev.mysql.com/doc/refman/5.0/en/show-profile.html

使用方法簡單來說:

Mysql > set profiling = 1;

Mysql>show profiles;

Mysql>show profile for query 1;

clip_image003

 

這個數據中就可以看到MyISAM的Sending data比InnoDB的Sending data費時太多了。查看mysql文檔

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是去磁盤中讀取select的結果,然后將結果返回給客戶端。這個過程會有大量的IO操作。你可以使用show profile cpu for query XX;來進行查看,發現MyISAM的CPU_system比InnnoDB大很多。至此可以得出結論是MyISAM進行表查詢(區別僅僅使用索引就可以完成的查詢)比InnoDB慢。

 

至於再往下的為什么,我想就需要看源碼了..於是,就此打住。

 

附帶一篇文章,里面還有status的用法

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

 

參考文章:

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


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