CODEWITHSUNDEEP
redis
Ram
Ram

Reputation: 11

Is there a feature to maintain the cardinality of the sorted sets in redis a constant?

Example, I want a key (sorted set) to store only 200 elements. If a new element is added (always with highscore) to the set, an element with lowest score in the set should be deleted automatically, maintaining the cardinality of sorted set a constant.

Upvotes: 1

Views: 257

Answers (1)

Itamar Haber
Itamar Haber

Reputation: 49942

No, there's no such feature per se, but it's very easy to achieve just that.

First, remember that members are unique so there could be a situation (unless in your use case this isn't so) where adding a new member with a new (high) score will actually update the score of an existing member. So, after each ZADD to your key, do ZCARD, e.g.:

c = redis.zcard('key')

If ZCARD's response is > 200, use the difference to trim the sorted set by rank with ZREMRANGEBYRANK:

if c > 200:
   r.zremrangebyrank('key', 0, c - 200 -1)

(BTW, if you're only adding one member at a, the above will always remove just one [the lowest ranked] member)

Upvotes: 2

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