Re: Unsynchronized parallel dumps from 13.3 replica produced by pg_dump

Chris Williams <cswilliams(at)gmail(dot)com> writes:
> We have a script that runs a pg_dump off of an RDS PG13.3 replica several
> times per day. We then load this dump using pg_restore into another
> postgres RDS db in another AWS account, scrub some of the data, and then
> take a snapshot of it.

Hmm ... I'm fairly sure that RDS Postgres is not Postgres at this level
of detail. The info I've been able to find about their replication
mechanism talks about things like "eventually consistent reads", which
is not something community Postgres deals in.

In particular, what I'd expect from the community code is that a replica
could see a sequence as being *ahead* of the value that you might expect
from looking at related tables; but never behind. (Also, that statement
is true regardless of whether you are doing parallel dump.) And
non-sequence tables should always be consistent, period.

So I'm suspicious that this is an RDS-specific effect, and thus that
you should consult Amazon support first. If they say "no, it's Postgres
all the way down", then we need to look closer.

regards, tom lane