Comparison
Snapshot expiryvsTime travel
Snapshot expiry
you deleted the rows a month ago and the bytes were still in the bucket, because the old snapshots still referenced them.
The maintenance operation that drops old table versions and physically removes the files only they referenced. Until it runs, deleted data is still on disk and still costs money, and it is still readable by anyone who can query an old snapshot. That makes it a privacy control as much as a cost control, and it is the step most often missing when a team implements erasure requests against a lakehouse.
Full entry →Time travel
you queried the table as it stood before this morning's bad run, without restoring anything.
Querying a previous version of a table by snapshot id or timestamp, made possible because a table version is a list of immutable files. It turns a class of recovery from an incident into a select statement, and it makes auditing and debugging a bad load dramatically cheaper. Its limit is retention: snapshots expire, and expiry is what allows deleted files to actually be deleted, which matters both for cost and for privacy requests.
Full entry →