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Redis · Concept

HyperLogLog

Redis HyperLogLog estimates the number of distinct values with low, bounded memory use. It trades exactness for a standard error rate of 0.81%.

Last updated

Since
2.8.9

Syntax

PFADD key [element ...]
PFCOUNT key [key ...]
PFMERGE destination source [source ...]

In-depth API docs are only for subscribers: parameters, examples, common mistakes and interview practice.

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  • PFADD
  • PFCOUNT
  • PFMERGE
  • cardinality
  • probabilistic data structure

Source: HyperLogLog. Checked 2026-11-03.