Horton

Re: Logical Replication of sequences

shveta malik <shveta.malik@gmail.com>

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From: shveta malik <shveta.malik@gmail.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: vignesh C <vignesh21@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>, Dilip Kumar <dilipbalaut@gmail.com>, Peter Smith <smithpb2250@gmail.com>, Shlok Kyal <shlok.kyal.oss@gmail.com>, Chao Li <li.evan.chao@gmail.com>, Nisha Moond <nisha.moond412@gmail.com>, Peter Eisentraut <peter@eisentraut.org>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Euler Taveira <euler@eulerto.com>, Michael Paquier <michael@paquier.xyz>, "Jonathan S. Katz" <jkatz@postgresql.org>, "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>, shveta malik <shveta.malik@gmail.com>
Date: 2025-10-27T08:42:33Z
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 →

  1. Doc: Add documentation for sequence synchronization.

  2. Remove unused assignment in CREATE PUBLICATION grammar.

  3. Add seq_sync_error_count to subscription statistics.

  4. Fix few issues in commit 5509055d69.

  5. Add sequence synchronization for logical replication.

  6. Add worker type argument to logical replication worker functions.

  7. Introduce "REFRESH SEQUENCES" for subscriptions.

  8. Refactor logical worker synchronization code into a separate file.

  9. Standardize use of REFRESH PUBLICATION in code and messages.

  10. Add "ALL SEQUENCES" support to publications.

  11. Expose sequence page LSN via pg_get_sequence_data.

  12. Resume conflict-relevant data retention automatically.

  13. Post-commit review fixes for 228c370868.

  14. Generate GUC tables from .dat file

On Sat, Oct 25, 2025 at 12:16 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Fri, Oct 24, 2025 at 11:43 AM shveta malik <shveta.malik@gmail.com> wrote:
> >
> > 5)
> > For the race condition where the worker is going to access the seq
> > locally and meanwhile it is altered; now the worker correctly reports
> > this. But it reports this as a success scenario. And once the scenario
> > is reported as 'seq-worker finished', we do not expect it to start
> > running again without the user doing REFRESH. But in this case, it
> > runs, see logs. Also it starts immediately for once due to the same
> > reason that start_time is reset in the success scenario.
> > -------
> > 17:35:05.618 IST [132551] LOG:  logical replication apply worker for
> > subscription "sub1" has started
> > 17:35:05.637 IST [132553] LOG:  logical replication sequence
> > synchronization worker for subscription "sub1" has started
> > 17:35:05.663 IST [132553] LOG:  logical replication sequence
> > synchronization for subscription "sub1" - total unsynchronized: 1
> > 17:36:11.987 IST [132553] LOG:  skip synchronization of sequence
> > "public.myseq249" because it has been altered concurrently
> > 17:36:19.614 IST [132553] LOG:  logical replication sequence
> > synchronization for subscription "sub1" - batch #1 = 1 attempted, 0
> > succeeded, 1 skipped, 0 mismatched, 0 insufficient permission, 0
> > missing from publisher
> > 17:36:20.335 IST [132553] LOG:  logical replication sequence
> > synchronization worker for subscription "sub1" has finished
> > 17:36:20.435 IST [132586] LOG:  logical replication sequence
> > synchronization worker for subscription "sub1" has started
> > 17:36:20.545 IST [132586] LOG:  logical replication sequence
> > synchronization for subscription "sub1" - total unsynchronized: 1
> > -------
> >
> > The behaviour looks slightly odd. Is there anything we can do about
> > this? Shall the skipped case be reported as ERROR due to the fact that
> > we leave it in state 'i' in pg_subscription_rel?
> >
>
> The downside of reporting an ERROR as soon as we can't sync values for
> one of the sequences is that the other sequences which could be synced
> won't get synced.

Yes, I agree.

> The other possibility is that we skip processing
> such a sequence while copying sequences but at the end if there is any
> pending sequence which is not synced, we raise an ERROR. If we do that
> then we may need to give some generic ERROR because there could be
> multiple such sequences. The other possibility is that we can give a
> LOG message like "logical replication sequence sync worker for
> subscription \"%s\" will restart because ..." and then do proc_exit(1)
> without resetting restart_time. Will that help to address your
> concern?
>

Thanks for suggesting these potential solutions. After reviewing the
new approach proposed in [1] by Hou-San, I believe this race condition
is no longer applicable, so we’re safe.

[1]: https://www.postgresql.org/message-id/TY4PR01MB169078D0BB792F1EE438A2EE294FCA%40TY4PR01MB16907.jpnprd01.prod.outlook.com

thanks
Shveta