时间:2021-07-01 10:21:17 帮助过:37人阅读
在平时的mysql文档学习中我们经常会看到这么一句话:
MySQL tries to leave space so that future inserts do not incur un-necessary page splits (and thus higher IO cost). In an "ideal" world, MySQL tries to keep the index pages at 15/16-th full, but depending on insert order, this fill factor can be as low as 1/2
大致含义就是当我们按照索引顺序插入时,page的填充率能达到15/16 , 而乱序插入时只能到略大于 1/2 的填充率。
那么这个说法是否正确呢?是否有相应的理论依据呢?
本文将通过一些测试来验证这个观点的真伪。
简介: 顺序数据通过sysbench --oltp-table-size = 8000000 生成,然后通过order by rand() 生成乱序数据。
mysql> desc sbtest;+-------+------------------+------+-----+---------+----------------+| Field | Type | Null | Key | Default | Extra |+-------+------------------+------+-----+---------+----------------+| id | int(10) unsigned | NO | PRI | NULL | auto_increment || k | int(10) unsigned | NO | MUL | 0 | || c | char(120) | NO | | | || pad | char(60) | NO | | | |+-------+------------------+------+-----+---------+----------------+bitsCN.com