Clickhouse

ClickHouse's SLRU Cache Gives Hot Entries a Second Queue

Oct 23, 2026 20 min read Jay Hubbert

ClickHouse’s default cache policy is SLRU, not LRU: entries hit twice are promoted to a protected queue that a sequential scan cannot flush.

Oct 23, 2026 22 min read Jay Hubbert

ClickHouse hashes each async insert into a per-key buffer and flushes it on size, count, or an adaptive deadline.

Oct 23, 2026 17 min read Jay Hubbert

ClickHouse resolves an INSERT’s columns by name into a sample block, then squashes, dedup-stamps and fans the data out to the sinks.

Oct 23, 2026 14 min read Jay Hubbert

ClickHouse scores each projection by the marks it must read, including the parts it cannot serve, and picks the cheapest.

Oct 23, 2026 13 min read Jay Hubbert

A RECOMPRESS TTL rewrites a whole part with a new codec once all of its rows have expired.