redis相關知識(五)

1.7 zset 結構

首先，介紹一下 skip list 的概念，然後再分析 zset 的實現.

1.7.1 Skip List 介紹1.7.1.1 有序鏈表

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 containing x, or the smallest element with a key larger than x (if x does 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(跳躍表)定義

SKIP LIST : A data structure for maintaing a set of keys in a sorted order.

Consists of several levels.

All keys appear in level 1

Each level is a sorted list.

If key x appears in level i, then it also appears in all levels below i

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An element in level i points (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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