Every write to an Apache Iceberg table creates a snapshot. Because old snapshots are kept, you can query the table exactly as it looked at an earlier point in time.
Query a past version
In Trino you can read a table at a snapshot or at a timestamp:
SELECT count(*) FROM events FOR VERSION AS OF 8954597067493422955;
SELECT count(*) FROM events FOR TIMESTAMP AS OF TIMESTAMP '2026-10-01 00:00:00 UTC';Why it matters
- Debugging: compare today's table with yesterday's to find a bad load.
- Audit: reproduce a report exactly as it was produced.
- Rollback: return to a known-good snapshot after a faulty job.
Keep storage under control
Old snapshots take space. Expire them on a schedule, and keep the window long enough for your audit needs. Catalogs such as Nessie add Git-like branches on top, so you can test changes safely before publishing them.