How Ctrl-C Reaches a Running Query: The Client's Cancel Packet
Ctrl-C only flips an atomic counter in the client; the receive loop notices, writes a Cancel packet, and keeps draining packets so the connection stays in sync.
Clickhouse
How the ClickHouse Client Splits a Script into Queries
The client parses a script statement by statement, ends inline INSERT data at a blank line, and pulls the trailing comment (and its test hint) into the statement it belongs to.
ClickHouse Builds an Actions DAG Once and Runs It on Every Block
ClickHouse compiles a SELECT into an ActionsDAG and reuses the sorted plan for every block.
ClickHouse Coordinates a Cluster-Wide Backup with ZooKeeper
A cluster-wide backup is a ZooKeeper-coordinated election: one owner per data file, a stage barrier between phases, and a consensus loop over metadata.
ClickHouse Deletes Expired TTL Rows Only When Parts Merge
ClickHouse stores a per-part TTL expiry bound and removes expired rows during a merge, using a bit mask rather than a rewrite.