How ClickHouse Batches Async Inserts in a Per-Key Queue
ClickHouse hashes each async insert into a per-key buffer and flushes it on size, count, or an adaptive deadline.
Internals
How ClickHouse Maps an INSERT onto the Table's Schema
ClickHouse resolves an INSERT’s columns by name into a sample block, then squashes, dedup-stamps and fans the data out to the sinks.
How ClickHouse Picks a Projection to Read
ClickHouse scores each projection by the marks it must read, including the parts it cannot serve, and picks the cheapest.
How ClickHouse Recompresses a Part When Its TTL Expires
A RECOMPRESS TTL rewrites a whole part with a new codec once all of its rows have expired.
How ClickHouse Splits a Session Context from a Query Context
ClickHouse splits session state from per-query state, and gates every setting change through a constraint checker.