ksck checksum scans can fail when the time to run takes longer than the default ancient history mark. This happened on a cluster wide checksum scan and a table specific checksum scan.
T 6e0de2a404d5468aaf20476ca42153f0 P f3d28930fbb34d889b982ac6efb1f8ad (cdhwn063.telecomitalia.local:7050): Error: Invalid argument: Snapshot timestamp is earlier than the ancient history mark. Consider increasing the value of the configuration parameter --tablet_history_max_age_sec. Snapshot timestamp: P: 1532368409711384 usec, L: 3 Ancient History Mark: P: 1532368439785390 usec, L: 0 Physical time difference: -30.074s
The error message is clear, but perhaps we could improve the logic to make failure less likely on large clusters or tables with a default ancient history mark.