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Redis Sets and Sorted Sets

type: conceptconfidence: highupdated: 2026-06-25sources: 2

Sets

A Redis set is an unordered collection of unique strings (members). Sets efficiently track unique items, represent relations, and perform set operations. Adding, removing, and membership tests are O(1).

  • SADD key member... — add members (creates the key); duplicates are silently ignored.
  • SREM, SCARD (count, O(1)), SISMEMBER / SMISMEMBER (membership, O(1)), SMEMBERS (all members, O(N)), SSCAN (iterative), SPOP, SRANDMEMBER, SMOVE.
  • Combinations: SINTER, SUNION, SDIFF (and SINTERCARD plus the ...STORE variants that save results to a key).
> SADD bikes:racing:france bike:1 bike:2 bike:3
(integer) 3
> SADD bikes:racing:usa bike:1 bike:4
(integer) 2
> SINTER bikes:racing:france bikes:racing:usa
1) "bike:1"
> SDIFF bikes:racing:france bikes:racing:usa
1) "bike:3"
2) "bike:2"

Max set size is 2^32 - 1 (4,294,967,295) members. SMEMBERS is O(n) and returns the whole set — prefer SSCAN for large sets. For approximate membership with low memory, consider a Bloom or Cuckoo filter (see probabilistic and geospatial).

Sorted sets

A sorted set is a collection of unique strings (members) ordered by an associated floating-point score; members with equal scores are ordered lexicographically. Use cases include leaderboards and sliding-window rate limiters.

  • ZADD key score member [score member ...] — add members or update scores (creates the key); O(log(N)) per item.
  • ZSCORE / ZMSCORE, ZINCRBY, ZCARD, ZRANK / ZREVRANK, ZCOUNT, ZREM.
> ZADD racer_scores 10 "Norem"
(integer) 1
> ZADD racer_scores 8 "Sam-Bodden" 10 "Royce" 6 "Ford" 14 "Prickett"
(integer) 4

Operating on ranges

  • ZRANGE key start stop — members by index range (with BYSCORE, BYLEX, REV, LIMIT options); O(log(N)+M).
  • ZRANGEBYSCORE key min max — members within a score range (-inf/+inf supported).
  • ZRANGEBYLEX / ZLEXCOUNT — lexicographical range queries.
  • ZREVRANGE, ZRANGEBYSCORE, ZPOPMIN / ZPOPMAX (and blocking BZPOPMIN/BZPOPMAX/BZMPOP), ZREMRANGEBY*.
> ZRANGEBYSCORE racer_scores -inf 10
1) "Ford"
2) "Sam-Bodden"
3) "Norem"
4) "Royce"

Most sorted set operations are O(log(n)); ZRANGE is O(log(n)+m) — use caution with large return values.

Related: data types overview, probabilistic and geospatial, json, redis cli.