http://dev.mysql.com/doc/refman/5.1/en/innodb-buffer-pool.html
buffer pool可以按page为单位,对记录进行缓存.
CREATE TABLE `20130122handler` ( `id` int(11) NOT NULL AUTO_INCREMENT, `uid` int(11) NOT NULL, `content` varchar(50) NOT NULL, PRIMARY KEY (`id`), KEY `20130122handler_idx_uid` (`uid`) ) ENGINE=InnoDB
这个表里有60w随机数据
先执行下
show status like 'Innodb_buffer_pool_read%';
结果为
Innodb_buffer_pool_read_requests 1204
Innodb_buffer_pool_reads 97
然后执行
select * from 20130122handler where uid=4349023;
用时为0.016s
show status like 'Innodb_buffer_pool_read%';
结果为
Innodb_buffer_pool_read_requests 1221
Innodb_buffer_pool_reads 98
观察下数据,发现Innodb_buffer_pool_reads增加了.
说明这条数据不在buffer pool中,需要从硬盘中读取
再执行一遍
select * from 20130122handler where uid=4349023;
用时为0s
观察下使用情况
Innodb_buffer_pool_read_requests 1237
Innodb_buffer_pool_reads 98
显然这次只需要读取buffer pool的数据就行了,省了一次磁盘IO
按照page来缓存,好处是连续读取同一个page上记录,只有第一个有磁盘IO.
也有人提出用按照row来缓存
http://rdc.taobao.com/team/jm/archives/1107
buffer pool有被污染的情况,即有些非热点数据把热点数据挤出了buffer pool
http://www.orczhou.com/index.php/2010/05/innodb-plugin-make-buffer-cache-scan-resistant/
buffer pool在启动的时候是空的,最好能预先warm up一下
http://www.mysqlperformanceblog.com/2008/05/01/quickly-preloading-innodb-tables-in-the-buffer-pool/
不过mysql 5.6有了新功能,可以关闭的时候dump出buffer pool镜像,然后启动的时候reload.
http://dev.mysql.com/doc/refman/5.6/en/glossary.html#glos_warm_up