Redis knowledge (5)

1.7 zset Structure

First, introduce the concept of skip list, and then analyze the implementation of zset.

1.7.1 introduction to Skip List 1.7.1.1 ordered linked List

1) Searching a key in a Sorted linked list

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// Searching an element <em> xcell * p = head; while (p-> next-> key <x) p = p-> next; return p;

Note: we return the element proceeding either the element containingX, Or the smallest element with a key largerX(IfXDoes not exists)

2) inserting a key into a Sorted linked list

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// To insert 35-p = find (35); CELL * p1 = (CELL *) malloc (sizeof (CELL); p1-> key = 35; p1-> next = p-> next; p-> next = p1;

3) deleteing a key from a sorted list

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// To delete 37-p = find (37); CELL * p1 = p-> next; p-> next = p1-> next; free (p1 );

1.7.1.2 SkipList (skip table) Definition

Skip list: A data structure for maintaing a set of keys in a sorted order.

Consists of severalLevels.

All keys appear in level 1

Each level is a sorted list.

If keyXAppears in levelI, Then it also appears in all levels belowI

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An element in levelIPoints (via down pointer) to the element with the same key in the level below.

In each level the keys and appear. (In our implementation, INT_MIN and INT_MAX

Top points to the smallest element in the highest level.

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