一切源于一個實驗，請看下面的例子：

表：

復制代碼 代碼如下:

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）

復制代碼 代碼如下:

<?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";

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

確定兩邊都沒有使用index，第二個查詢查的rows，并且MyISAM的查詢rows還比InnoDB少這么多，反而是查詢慢于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：

使用方法簡單來說：

復制代碼 代碼如下:

Mysql > set profiling = 1;

Mysql>show profiles;

Mysql>show profile for query 1;

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。