Efficiently traversing InnoDB B+Trees with the page directory--slot

Efficientlytraversing InnoDB B+Trees with the page directory

1、the purpose of the page directory

As described in the posts mentioned above,all records in INDEX pages are linked together in a singly-linked list inascending order. However, list traversal through a page with potentiallyseveral hundred records in it is very expensive: every record’s key must becompared, and this needs to be done at each level of the B+Tree until therecord sought is found on a leaf page.

Index page页中的所有记录都以单链表递增的形式串联。但是在一页中以链表的形式检索记录代价很大：每一个记录的key必须比较，这个动作需要在所有高度的B+树上进行，知道在叶子节点找到记录。

 

The page directory greatly optimizes thissearch by providing a fixed-width data structure with direct pointers to 1 ofevery 4-8 records, in order.