clustered index 考古
背景
我们经常使用的mysql有时候会有cludter index的概念，有时候我们会将这个词翻译成聚簇索引。在mysql上是这样说的：
在17.6.2.1 Clustered and Secondary Indexes章节，mysql的文档是这样说的：
Each
InnoDBtable has a special index called the clustered index that stores row data. Typically, the clustered index is synonymous with the primary key. To get the best performance from queries, inserts, and other database operations, it is important to understand howInnoDBuses the clustered index to optimize the common lookup and DML operations.
然后我们看到论文Access Path Selection in a Relational Database Management System
If the tuples are inserted into segment pages in the index ordering, and if this physical proximity corresponding to index key value is maintained, we say that the index is clustered
如果元组按照索引顺序插入到段页面中，并且如果索引键和索引值都是物理上在一起的，我们称这个索引为聚集索引
