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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。
测试数据准备简介： 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 | | | |+-------+------------------+------+-----+---------+----------------+
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