Horton

Re: Logical Replication of sequences

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>
Cc: Dilip Kumar <dilipbalaut@gmail.com>, "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>, vignesh C <vignesh21@gmail.com>, Peter Smith <smithpb2250@gmail.com>, shveta malik <shveta.malik@gmail.com>, Shlok Kyal <shlok.kyal.oss@gmail.com>, Chao Li <li.evan.chao@gmail.com>, Masahiko Sawada <sawada.mshk@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>
Date: 2025-10-17T04:31:42Z
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 Thu, Oct 16, 2025 at 4:53 PM Zhijie Hou (Fujitsu)
<houzj.fnst@fujitsu.com> wrote:
>
> Regarding whether we can avoid creating slot/origin for seq-only publication.
> I think the main challenge lies in ensuring the apply worker operates smoothly
> without a replication slot. Currently, the apply worker uses the
> START_REPLICATION command with a replication slot to acquire the slot on the
> publisher. To bypass this, it's essential to skip starting the replication and
> specifically, avoid entering the LogicalRepApplyLoop().
>
> To address this, I thought to implement a separate loop dedicated to
> sequence-only subscriptions. Within this loop, the apply worker would only call
> functions like ProcessSyncingSequencesForApply() to manage sequence
> synchronization while periodically checking for any new tables added to the
> subscription. If new tables are detected, the apply worker would exit this loop
> and enter the LogicalRepApplyLoop().
>
> I chose not to consider allowing the START_REPLICATION command to operate
> without a logical slot, as it seems like an unconventional approach requiring
> modifications in walsender and to skip logical decoding and related processes.
>
> Another consideration is whether to address scenarios where tables are
> subsequently removed from the subscription, given that slots and origins would
> already have been created in such cases.
>
> Since it might introduce addition complexity to the patches, and considering
> that we already allow slot/origin to be created for empty subscription, it might
> also be acceptable to allow it to be created for sequence-only subscription. So,
> I chose to add some comments to explain the reason for it in latest version.
>
> Origin case might be slightly easier to handle, but it could also require some
> amount of implementations. Since origin is less harmful than a replication slot
> and maintaining it does not have noticeable overhead, it seems OK to me to
> retain the current behaviour and add some comments in the patch to clarify the
> same.
>

I agree that avoiding to create a slot/origin for sequence-only
subscription is not worth the additional complexity at other places,
especially when we do create them for empty subscriptions.

-- 
With Regards,
Amit Kapila.