Sorted sets
In Redis, the sorted-set data type combines the characteristics of both Redis lists and sets. Similarly to those of a Redis list, a sorted set's values are ordered, and like a set, each value is assured to be unique. Of all the various data structures in Redis, the sorted set is the closest to a killer feature. The flexibility of a sorted set allows for multiple types of access patterns depending on the needs of the application. Using a single sorted set for a player's scores in a game both the top and the bottom players are easily fetched for a leaderboard by either the ZRANGE or ZREVRANGE Redis commands.
For sorted sets, the ZADD command adds a member with a score to the sorted set. The time complexity of ZADD is O(log(n)), meaning that as the size of the sorted set increases, the rate of increase in the processing time is a constant. Therefore, the difference between adding a new member to a large sorted set is trivial; the difference between log(10000) ~ 9.21034037...
