Re: Logical Replication of sequences

On Tue, May 20, 2025 at 8:35 AM Nisha Moond <nisha(dot)moond412(at)gmail(dot)com> wrote:
>
> >
> > Thanks for the comments, these are handled in the attached v20250516
> > version patch.
> >
>
> Thanks for the patches. Here are my review comments -
>
> Patch-0004: src/backend/replication/logical/sequencesync.c
>

Hi,

Currently, the behavior of the internal query used to fetch sequence
info from the pub is inconsistent and potentially misleading.

case1: If a single non-existent sequence is passed (e.g., VALUES
('public','n10')), the query throws an ERROR, so we get error on sub -
ERROR: could not receive list of sequence information from the
publisher: ERROR: sequence "public.n10" does not exist

case2: If multiple non-existent sequences are passed (e.g., VALUES
('public','n8'),('public','n9')), it silently returns zero rows,
resulting only in a LOG message instead of an error.
LOG: Logical replication sequence synchronization for subscription
"subs" - total unsynchronized: 2; batch #1 = 2 attempted, 0 succeeded,
0 mismatched

IMO, This inconsistency can be confusing for users. I think we should
make the behavior uniform. Either -
(a) Raise an error if any/all of the requested sequences are missing
on the publisher, or
(b) Instead of raising an error, emit a LOG(as is done in case2) and
maybe include the count of missing sequences too.

I'm fine with either option.

--
Thanks,
Nisha