HyperLogLog Commands

HyperLogLog is a probabilistic data structure used to estimate the cardinality (number of unique elements) of a set, using a small and fixed amount of memory.

• Approximate result: not exact, with a small error rate (typically ~0.81% in Redis-style HLL).
• Use cases: UV counting, unique search queries, deduplication statistics, etc.

Command List

PFADD

Adds elements to a HyperLogLog

PFCOUNT

Returns the estimated cardinality

PFMERGE

Merges multiple HyperLogLogs into one

Notes

• The returned cardinality is an estimate, not an exact count.
• In Redis, HyperLogLog is represented as a string internally. Rudis also reports TYPE as string for compatibility.