ClickHouse Splits Session State from Query State: SET and SETTINGS Land in Different Contexts
ClickHouse splits session state from per-query state, and gates every setting change through a constraint checker.
Clickhouse
ClickHouse Resolves an INSERT Into a Sample Block: The Client's Column Order Wins
ClickHouse resolves an INSERT’s columns by name into a sample block, then squashes, dedup-stamps and fans the data out to the sinks.
ClickHouse's numbers() Is a Generator, Not a Table: One Iota-Filled Block at a Time
numbers() is a generator that iota-fills one column per block and keeps only a counter in memory.
SummingMergeTree and AggregatingMergeTree Collapse Groups in the Merge: No Hash Table, No Second Table
SummingMergeTree and AggregatingMergeTree combine rows inside the merge algorithm, group by group, as the sorted streams are walked.
ClickHouse Incremental Backups Are Not Diffs: A Verified Byte Prefix and the Suffix After It
Incremental backups reuse the base backup’s bytes: only the suffix after a verified shared prefix is uploaded, and the restore concatenates the two halves.