MySQL TEXT内存分配

Question

任何人都知道 MySQL 如何为“TEXT”或“BLOB”等字段分配磁盘空间

例如，当我将 10kb 的字符串插入“TEXT”列时会发生什么？是分配了整个 65kb 数据还是仅分配了 10kb？

Answer 1

这在文档中有解释: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

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.

所以简而言之，整个 65kb 都没有浪费。