What is the underlying implementation principle of Redis ordered sets?

The underlying implementation principle of Redis sorted sets combines Skip List and Hash Table.

A skip list is an ordered data structure similar to a linked list, but with multiple pointers added to each node to allow for quick jumps to other nodes, speeding up search operations. Each node in the skip list holds a member and a score, sorted by the score in ascending order.

In Redis, each member of a sorted set corresponds to a score, which allows you to look up the score based on the member and quickly retrieve a list of members within a certain range based on the score. Redis uses skip lists to maintain the order of sorted sets, achieving fast range queries by maintaining multiple levels of sorted linked lists.

In addition to using skip lists, Redis also utilizes hash tables to store the members and their scores in sorted sets. The query operation time complexity of hash tables is O(1), allowing for quick retrieval of scores based on members.

By combining skip lists and hash tables, Redis achieves efficient operations such as querying, inserting, and deleting in sorted sets. Skip lists provide efficient ordering, while hash tables provide efficient lookups.