Horton

RE: Conflict detection for update_deleted in logical replication

Zhijie Hou (Fujitsu) <houzj.fnst@fujitsu.com>

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From: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>
To: Dilip Kumar <dilipbalaut@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>
Cc: shveta malik <shveta.malik@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>, pgsql-hackers <pgsql-hackers@postgresql.org>, vignesh C <vignesh21@gmail.com>, Nisha Moond <nisha.moond412@gmail.com>
Date: 2025-08-12T09:32:07Z
Lists: pgsql-hackers 
On Tuesday, August 12, 2025 5:01 PM Dilip Kumar <dilipbalaut@gmail.com> wrote:

Hi,

> 
> On Tue, Aug 12, 2025 at 2:21 PM Amit Kapila <amit.kapila16@gmail.com>
> wrote:
> >
> > On Tue, Aug 12, 2025 at 2:06 PM shveta malik <shveta.malik@gmail.com>
> wrote:
> > >
> > > 2)
> > > postgres=# create subscription sub2  connection 'dbname=postgres
> > > host=localhost user=shveta port=5433' publication pub2 WITH
> > > (retain_dead_tuples = false, max_conflict_retention_duration=1000);
> > > NOTICE:  created replication slot "sub2" on publisher CREATE
> > > SUBSCRIPTION
> > >
> > > Shall we give notice that max_conflict_retention_duration is ignored
> > > as retain_dead_tuples is false.
> > >
> >
> > How about disallowing this combination?
> 
> +1 to disallow that.

I think disallowing this case may not suffice, as users could initially set
(retain_dead_tuples=on, max_conflict_retention_duration=100) but later disable
retain_dead_tuples. This would result in the same state as
(retain_dead_tuples=off, max_conflict_retention_duration=100) unless we disallow
disabling rdt in this case as well.

So, do you think we should disallow both cases, or we only disallow setting
max_conflict_retention_duration for disabled retain_dead_tuples and give NOTICE
in another case ?

I personally prefer a consistent behavior, e.g., either we allow both cases and
give NOTICEs, or we disallow both cases. This is because, if the goal here to
prevent potential misconfigurations by users, the scenario where a user disables
retain_dead_tuples might also be considered a similar misconfiguration. So, I'm
a bit concerned that the benefits of imposing a partial restriction may not
outweigh the risk of generating inconsistent behavior. (And I did not see
similar precedent).

What do you think ?

Best Regards,
Hou zj

Commits

  1. Fix intermittent BF failures in 035_conflicts.

  2. Resume conflict-relevant data retention automatically.

  3. Fix intermittent test failure introduced in 6456c6e2c4.

  4. Fix Coverity issue reported in commit a850be2fe.

  5. Add test to prevent premature removal of conflict-relevant data.

  6. Post-commit review fixes for 228c370868.

  7. Add max_retention_duration option to subscriptions.

  8. Detect and report update_deleted conflicts.

  9. Preserve conflict-relevant data during logical replication.

  10. Integrate FullTransactionIds deeper into two-phase code

  11. Improve checks for GUC recovery_target_timeline

  12. Prevent excessive delays before launching new logrep workers.

  13. Keep WAL segments by slot's last saved restart LSN

  14. Rework some code handling pg_subscription data in psql and pg_dump

  15. Use generateClonedIndexStmt to propagate CREATE INDEX to partitions.