mysql優化 - 如何解釋mysql主鍵太長導致secondary indexes使用更多空間的問題, 如用uuid當主鍵導致這個問題

Question

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

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

例如 uuid 當主鍵, 主鍵空間就變大了, 為啥會導致secondary indexes空間佔用也大呢, 搞不明白

Answer 1

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 seconda ns for the row, as well as the columns specified for the seconda ns for the row as well as the columns specified for the secry sindex. search for the row in the clustered index.

這個是官方文件中的，意思是secondary index也會包含primary,所以你主鍵越大，secondary indexes空間佔用也越大

參考：https://dev.mysql.com/doc/ref...