PetSerAl <petseral@xxxxxxxxx> writes: > My question: > What happens if not MVCC-safe command committed after snapshot but before lock? Then you'd get a dump that's not exactly consistent with the state at the time of the snapshot. However, it would be the very same database state that any other query would see at that time. So if it's functionally inconsistent for your purposes, then you brought that on your own head by using TRUNCATE concurrently with other operations. The other thing I can think of that's a hazard in this area is that pg_dump will record current values of sequence objects that may be advanced beyond where the sequence was at the instant of the snapshot, since nextval() isn't MVCC-safe. There are a lot of other ways (rollbacks and crashes) in which a sequence can get advanced beyond the last derived value you can find in the database, so an application that finds this to be unacceptable should probably not be using sequences. regards, tom lane
