Data engineering·Files, formats and table layers
the update is written as a small delta file and the reader merges it with the base file every time, until a compaction folds them together.
Merge-on-read table
Also calledMoR table, delete vectors
A table where mutations are appended as delta or delete files and reconciled at query time. Writes are cheap and fresh, and every read pays a merge cost that grows until compaction runs. It is the right shape for frequently updated tables, and it makes compaction load-bearing rather than optional — an unmaintained merge-on-read table degrades continuously.