問題描述

我是看了美團的文章 : http://tech.meituan.com/MT_Le... 想到的, 不太明白

mysql官方原話是:

If the primary key is long, the secondary indexes use more space, so it is advantageous to have a short primary key

比如 uuid 當主鍵, 主鍵空間就變大了, 為啥會導致secondary indexes空間占用也大呢, 搞不明白

問題解答

All indexes other than the clustered index are known as secondary indexes. In InnoDB, each record in a secondary index contains the primary key columns for the row, as well as the columns specified for the secondary index. InnoDB uses this primary key value to search for the row in the clustered index.

這個是官方文檔中的，意思是secondary index也會包含primary,所以你主鍵越大，secondary indexes空間占用也越大

參考：https://dev.mysql.com/doc/ref...