ClickHouse Generates an Unbounded Number Stream in Constant Memory
numbers() is a generator that iota-fills one column per block and keeps only a counter in memory.
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ClickHouse Incremental Backups Store Only the Changed Tail of a File
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.
ClickHouse Keeper Carries a Tree Digest in Every Raft Log Entry
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.
ClickHouse Packs a HyperLogLog Rank Into Five Bits
ClickHouse’s CompactArray stores sub-byte values in a bitset and reads them through an unaligned 16-bit window, so a HyperLogLog rank costs 5 or 6 bits per bucket.
ClickHouse Pushes ORDER BY into the Storage Read
ClickHouse matches ORDER BY against the sorting key and reads MergeTree parts in key order instead of sorting everything.