Data engineering·Files, formats and table layers
someone switched the codec and the files got a third smaller while the queries got slightly slower to decode.
Compression codec
Also calledcompression algorithm, zstd vs snappy
The algorithm compressing each column chunk, chosen per table and traded off between file size and CPU on every read. On a per-byte-scanned billing model the smaller file is directly cheaper, so the choice is a money decision as much as a performance one. It is worth knowing as a lever because it is one of the few that can be changed by rewriting files, with no consumer needing to know.