一、前言
最近在刚完成了pw版本的升级程序，拿了个拥有3万多用户的小站跑了下，结果一次503的time out错误，最后修修补补跑完之后发现用了将近1个小时。于是将运行最慢的几个模块分析了下SQL语句。记录下。
二、环境描述
数据库：mysql，原数据和目标数据同一个服务。
操作系统：本地的ubuntu12.10
描述：原PW87：用户数据量3.4W，2.1W帖子数据，7.9W回复数据，3.1W原私信数据，数据库使用的引擎是myisam，
新pw9的数据库采用innodb引擎
二、sql记录分析
监听到一条用户数据查询如下：
select * from pw_members order by uid limit 10000, 1000;
用explain分析得到如下：
myiasm引擎：
mysql> explain select * from pw_members order by uid limit 10000, 1000;
+----+-------------+------------+------+---------------+------+---------+------+-------+----------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+------------+------+---------------+------+---------+------+-------+----------------+
| 1 | SIMPLE | pw_members | ALL | NULL | NULL | NULL | NULL | 34730 | Using filesort |
+----+-------------+------------+------+---------------+------+---------+------+-------+----------------+
1 row in set (0.00 sec)
innodb引擎：
mysql> explain select * from nw_user order by uid limit 10000, 1000;
+----+-------------+---------+-------+---------------+---------+---------+------+-------+-------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+---------+-------+---------------+---------+---------+------+-------+-------+
| 1 | SIMPLE | nw_user | index | NULL | PRIMARY | 4 | NULL | 11000 | |
+----+-------------+---------+-------+---------------+---------+---------+------+-------+-------+
1 row in set (0.01 sec)
两表使用都对uid建立唯一索引，
换种写法：
SELECT uid FROM pw_members WHERE uid > 10000 ORDER BY uid LIMIT 1000;
myisam引擎：
mysql> explain SELECT uid FROM pw_members WHERE uid > 10000 ORDER BY uid LIMIT 1000;+----+-------------+------------+-------+---------------+---------+---------+------+-------+--------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+------------+-------+---------------+---------+---------+------+-------+--------------------------+
| 1 | SIMPLE | pw_members | range | PRIMARY | PRIMARY | 4 | NULL | 26074 | Using where; Using index |
+----+-------------+------------+-------+---------------+---------+---------+------+-------+--------------------------+
innodb引擎：
mysql> explain select * from nw_user where uid > 10000 order by uid limit 10000, 1000;
+----+-------------+---------+-------+---------------+---------+---------+------+-------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+---------+-------+---------------+---------+---------+------+-------+-------------+
| 1 | SIMPLE | nw_user | range | PRIMARY | PRIMARY | 4 | NULL | 17461 | Using where |
+----+-------------+---------+-------+---------------+---------+---------+------+-------+-------------+
我的结论：
横向相比，对于第一种写法，innodb处理的方式会比myisam优雅点，而第二种写法则差不多。
纵向相比，则第二种写法处理起来无论在innodb或是myisam都比第一种写法优雅。
注：这次的数据量确实不大，所以得出这个结论也许有些站不住脚，等我遇到更大数据量的时候再来回头看看这个结论如何。
于是我将从myisam有主键的处理查询都改为第二种形式，从innodb处理的则根据情况处理。
三、
第一次处理这种数据转移，没有什么经验，也正在摸索阶段，希望各位大大么多多留言哈