citusdata/postgresql-hll

Health v2 · maintenance only

Adoption not part of the score

1230 stars · 115 forks observed · 2026-10-10

What it is AI-extracted, prompt v1, taxonomy v1, 2026-08-30, confidence not recorded

A PostgreSQL extension that adds HyperLogLog as a native data type for approximate distinct value counting with tunable precision. It uses a hierarchy of algorithms (EMPTY, EXPLICIT, SPARSE, FULL) to improve accuracy and memory efficiency over the original HLL paper.

Use cases

• count distinct values in postgres with low memory
• estimate unique visitors per day in sql
• compute approximate cardinality of billions of values
• run fast distinct count aggregations in analytics queries
• store probabilistic sets as a postgres column type
• merge hll sketches across distributed postgres nodes

When to choose

• you need approximate distinct counts at massive scale with tiny fixed memory footprint
• you want to aggregate and merge cardinality sketches directly in SQL
• you need tunable precision trading accuracy for storage in Postgres

When to avoid

• you need exact distinct counts rather than estimates
• you are not using PostgreSQL or a compatible database
• your cardinalities are small enough that plain COUNT(DISTINCT) is fast enough

Facets

library · maturity stable

database data-science analytics databases analytics big-data self-hosted postgresql-extension hyperloglog sketching distinct-count probabilistic-data-structures approximate-counting linux macos docker

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