ClickHouse JOINs Aren't Slow Anymore (You're Reading 2020's Docs)

Short summary

ClickHouse rebuilt its JOIN subsystem between 2022–2026, shipping six auto-selected algorithms and a query optimizer that achieves up to 1,450× speedup on complex queries. Grace hash spilling eliminates out-of-memory crashes; automatic subquery decorrelation eliminates manual rewrites. The 2020 advice to avoid JOINs is obsolete.

• •Six JOIN algorithms ship by default with automatic selection; grace hash spills to disk instead of OOMing
• •Query optimizer reorders joins using statistics, achieving 1,450× speedup on star-schema and multi-table workloads
• •Correlated subquery decorrelation now GA (Aug 2025), eliminating manual rewrites when migrating from PostgreSQL/Snowflake

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