Data engineering·Files, formats and table layers
updating one row rewrites the entire file that row lived in, so writes are slow and every read is as fast as a plain scan.
Copy-on-write table
Also calledCoW table
A table where mutations are applied by rewriting the affected data files immediately. Readers never do extra work, which makes it the right choice when reads vastly outnumber writes and freshness requirements are modest. The write amplification is the whole cost: a single-row change to a large file costs the whole file, which is why a high-frequency change feed into a copy-on-write table becomes expensive quickly.