ClickHouse Keeper's Raft Log Carries a Tree Digest: A Mismatch Terminates the Replica
Keeper puts a digest of its node tree inside every Raft log entry; a follower whose recomputed digest disagrees with the leader’s kills itself.
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ClickHouse Runs ON CLUSTER DDL Through ZooKeeper: The Result Is a Directory Listing
Distributed DDL is a ZooKeeper queue of sequential entries plus a per-host finished directory that the initiator lists to collect results.
ClickHouse Batches Async Inserts: A UInt128 Key Over the AST, the User and the Settings
ClickHouse hashes each async insert into a per-key buffer and flushes it on size, count, or an adaptive deadline.
ClickHouse Picks a Projection by Counting Marks: How a Secondary Index Beats the Primary One
ClickHouse scores each projection by the marks it must read, including the parts it cannot serve, and picks the cheapest.
ClickHouse's RECOMPRESS TTL Rewrites a Whole Part: The Part Remembers Which Codec It Wrote
A RECOMPRESS TTL rewrites a whole part with a new codec once all of its rows have expired.