ClickHouse Buffers the Query Log and Flushes It Into a Real MergeTree Table
The query log is an in-memory queue drained every 7.5 seconds by a background thread that INSERTs into a lazily created MergeTree table.
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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's JSON Type: A Column That Is a Tree of Subcolumns
ClickHouse’s JSON type splits a document into per-path subcolumns, with typed paths, bounded dynamic paths, and a shared-data spill.
ClickHouse Fuzzes Itself with Oracles: Two Runs, One MD5
BuzzHouse pairs every random query with an oracle query and compares the two result files by MD5 to catch wrong answers, not just crashes.
ClickHouse Chooses What Goes into PREWHERE by Cost per Rejected Row
ClickHouse moves WHERE conditions into PREWHERE by cost per rejected row, and reads PREWHERE columns in separate read steps.