Parallelizing ClickHouse aggregation merge for fixed hash map

T1Covered by 1 source · first reported by Databricks / ClickHouse / DuckDB / Supabase / Neon / PlanetScale at 16 Dec 2025, 10:13 UTC

A first-person engineering deep dive into how ClickHouse parallelized aggregation merges for FixedHashMap, including design choices, false starts, and performance trade-offs.

Sources

• T1Parallelizing ClickHouse aggregation merge for fixed hash mapDatabricks / ClickHouse / DuckDB / Supabase / Neon / PlanetScale16 Dec 2025, 10:13