ClickHouse JOIN performance was rebuilt between 2022 and 2026. The "avoid JOINs in ClickHouse" advice from 2020 is still circulating: "ClickHouse can't do JOINs." "Denormalize everything." "Only hash join is supported." "JOINs OOM on anything bigger than RAM." All four were accurate in 2020. None of them are accurate today. In 2020, ClickHouse had one join algorithm, no disk spilling, no cost-based optimizer, and join order followed query syntax. If the right table did not fit in memory, the query crashed. Between 2022 and early 2026, the join subsystem was rebuilt. Six algorithms ship by default. The optimizer reorders joins automatically using column statistics. Runtime bloom filters prune fact tables at the storage scan. Grace hash spills to disk instead of OOMing. None of it is behind feature flags. Here is what shipped. How Many JOIN Algorithms Does ClickHouse Support? By the end of 2022 ClickHouse had five join algorithms. Today it has six, and the engine selects automatically: Hash join. The classic.…