Home Database Mysql Tutorial MySQL 5.1分区技术初探(二)

MySQL 5.1分区技术初探(二)

Jun 07, 2016 pm 04:34 PM
mysql introduce Partition Preliminary exploration technology

2. MySQL分区介绍 MySQL的分区技术不同与之前的分表技术,它与水平分表有点类似,但是它是在逻辑层进行的水平分表,对与应用程序而言它还是一张表。 2.1 MySQL分区类型 MySQL5.1有5中分区类型: RANGE 分区:基于属于一个给定连续区间的列值,把多行分配给分

2. MySQL分区介绍
MySQL的分区技术不同与之前的分表技术,它与水平分表有点类似,但是它是在逻辑层进行的水平分表,对与应用程序而言它还是一张表。
2.1 MySQL分区类型
MySQL5.1有5中分区类型:
RANGE 分区:基于属于一个给定连续区间的列值,把多行分配给分区;
LIST 分区:类似于按RANGE分区,区别在于LIST分区是基于列值匹配一个离散值集合中的某个值来进行选择;
HASH分区:基于用户定义的表达式的返回值来进行选择的分区,该表达式使用将要插入到表中的这些行的列值进行计算。这个函数可以包含MySQL 中有效的、产生非负整数值的任何表达式。
KEY 分区:类似于按HASH分区,区别在于KEY分区只支持计算一列或多列,且MySQL 服务器提供其自身的哈希函数。
2.2 RANGE分区
对于RANGE分区,举个例子:
例1. 假定你创建了一个如下的一个表,该表保存有20家音像店的职员记录,这20家音像店的编号从1到20。 如果你想将其分成4个小分区,那么你可以采用RANGE分区,创建的数据库表如下:

这个例子,它的key是一个整型的数据,那是否对于其它类型的字段就无法作为key呢?  答案是否定的,例子2说明这种情况。
例2. 假定你创建了一个如下的一个表,该表保存有20家音像店的职员记录,这20家音像店的编号从1到20。你想把不同时期离职的员工进行分别存储,那么你可以将日期字段separated(即离职时间)作为一个key,创建的SQL语句如下:

这样你就可以对一个日期类型的字段调用mysql的日期函数YEAR()转换为一种整数类型,从而可以作为RANGE分区的key。这个时候,你可以看到,按照分区后的物理文件是相对独立的:

可知,每个分区有自己独立的数据文件和索引文件,这是为什么你对某一个查询,它只会访问它需要访问的数据块,而不访问根本不是结果的物理块,从而可以大大提高系统的效率。

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