Re: Logical Replication of sequences

Nisha Moond <nisha.moond412@gmail.com>

From: Nisha Moond <nisha.moond412@gmail.com>

To: vignesh C <vignesh21@gmail.com>

Cc: Peter Smith <smithpb2250@gmail.com>, shveta malik <shveta.malik@gmail.com>, "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>, Masahiko Sawada <sawada.mshk@gmail.com>, Shlok Kyal <shlok.kyal.oss@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>, Peter Eisentraut <peter@eisentraut.org>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Euler Taveira <euler@eulerto.com>, Michael Paquier <michael@paquier.xyz>, "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>, "Jonathan S. Katz" <jkatz@postgresql.org>

Date: 2025-05-20T09:05:40Z

Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

Doc: Add documentation for sequence synchronization.
- 55cefadde874 19 (unreleased) landed
Remove unused assignment in CREATE PUBLICATION grammar.
- bfb7419b0bbe 19 (unreleased) landed
Add seq_sync_error_count to subscription statistics.
- f6a4c498dcf6 19 (unreleased) landed
Fix few issues in commit 5509055d69.
- 5a4eba558aa7 19 (unreleased) landed
Add sequence synchronization for logical replication.
- 5509055d6956 19 (unreleased) landed
Add worker type argument to logical replication worker functions.
- 3e8e05596a02 19 (unreleased) landed
Introduce "REFRESH SEQUENCES" for subscriptions.
- f0b3573c3aac 19 (unreleased) landed
Refactor logical worker synchronization code into a separate file.
- 41c674d2e31e 19 (unreleased) landed
Standardize use of REFRESH PUBLICATION in code and messages.
- 2436b8c047ff 19 (unreleased) landed
Add "ALL SEQUENCES" support to publications.
- 96b378497346 19 (unreleased) landed
Expose sequence page LSN via pg_get_sequence_data.
- b93172ca59f4 19 (unreleased) landed
Resume conflict-relevant data retention automatically.
- 0d48d393d465 19 (unreleased) cited
Post-commit review fixes for 228c370868.
- 1f7e9ba3ac4e 19 (unreleased) cited
Generate GUC tables from .dat file
- 63599896545c 19 (unreleased) cited

On Tue, May 20, 2025 at 8:35 AM Nisha Moond <nisha.moond412@gmail.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