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[MySQL]InnoDB逻辑存储结构

 

InnoDB存储引擎中的表非常像Oracle中的索引组织表,每张表必须得有主键,如果表在创建时没有显示定义主键,则根据以下原则自动创建主键:

 

1)如果有非空的唯一索引,则该索引所在的列为主键;

2)如果不符合上述条件,自动创建一个6个字节的指针为主键。

 

InnoDB存储引擎的逻辑存储结构和Oracle几乎一样,从大到小分别为:表空间、段、区、页,它们的关系如下图所示:

 

[MySQL]InnoDB逻辑存储结构_MySQL

 

表空间

在上一篇《MySQL InnoDB文件介绍》http://www.bitsCN.com/database/201306/219327.html中,我们知道InnoDB有一个默认的表空间,如果我们启用了参数innodb_file_per_table,则针对每张可以单独放在表空间里。这里需要注意的是,即时启用了innodb_file_per_table,也并不是表中所有的数据都单独放在自己的表空间里,单独表空间只存放数据、索引和插入缓冲,其它如Undo、系统事务信息、二次写缓冲等还是存放在默认共享表空间里。

 

表空间有若干各段组成,常见的有数据段、索引段、回滚段等。前面提到InnoDB中的表是索引组织表,因此数据段也称为leaf node segment,索引段也称为non-leaf node segment。

 

每64个连续的页组成区,因此区大小正好为1M。

 

页是InnoDB磁盘管理的最小单位,固定大小为16K,不可以更改(也许通过更改源码可以修改固定大小)。

 

InnoDB表中数据按行存储。
 

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