MySQL TEXT内存分配 [英] MySQL TEXT memory allocation

问题描述

任何人都知道MySQL如何为"TEXT"或"BLOB"之类的字段分配磁盘空间

Anybody knows how MySQL allocates disk space for fields like "TEXT" or "BLOB"

例如，当我在"TEXT"列中插入10kb字符串时会发生什么?是分配了整个65kb的数据还是只有10kb?

For example, what happens when I insert 10kb string into "TEXT" column? Is the entire 65kb data allocated or only 10kb?

推荐答案

文档中对此进行了解释:

This is explained in the documentation: http://dev.mysql.com/doc/refman/5.7/en/storage-requirements.html

BLOB, TEXT              L + 2 bytes, where L < 2^16
MEDIUMBLOB, MEDIUMTEXT  L + 3 bytes, where L < 2^24 
LONGBLOB, LONGTEXT      L + 4 bytes, where L < 2^32

可变长度字符串类型使用长度前缀加 数据.长度前缀需要1到4个字节，具体取决于 数据类型，并且前缀的值为L( 字符串).例如，存储MEDIUMTEXT值需要L 字节来存储值，再加上三个字节来存储值的长度 值.

Variable-length string types are stored using a length prefix plus data. The length prefix requires from one to four bytes depending on the data type, and the value of the prefix is L (the byte length of the string). For example, storage for a MEDIUMTEXT value requires L bytes to store the value plus three bytes to store the length of the value.

简而言之，整个65kb不会浪费.

So in short, the whole 65kb is not wasted.

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