Horton

Re: Conflict detection for update_deleted in logical replication

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: Masahiko Sawada <sawada.mshk@gmail.com>
Cc: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>, Nisha Moond <nisha.moond412@gmail.com>, "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>, shveta malik <shveta.malik@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2025-01-16T10:56:39Z
Lists: pgsql-hackers 
On Wed, Jan 15, 2025 at 9:38 AM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Wed, Jan 15, 2025 at 5:57 AM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> >
> > Probably retaining dead tuples based on the time duration or its age
> > might be other solutions, it would increase a risk of not being able
> > to detect update_deleted conflict though. I think in any way as long
> > as we accumulate dead tulpes to detect update_deleted conflicts, it
> > would be a tradeoff between reliably detecting update_deleted
> > conflicts and the performance.
> >
>
> Right, and users have an option for it. Say, if they set max_lag as -1
> (or some special value), we won't invalidate the slot, so the
> update_delete conflict can be detected with complete reliability. At
> this stage, it is okay if this information is LOGGED and displayed via
> a system view. We need more thoughts while working on the CONFLICT
> RESOLUTION patch such as we may need to additionally display a WARNING
> or ERROR if the remote_tuples commit_time is earlier than the last
> time slot is invalidated.
>

The more reliable way to do something in this regard would be that if
there is a valid and active pg_conflict_detection (or whatever we name
this slot) then consider the update_missing conflict detected as
reliable. Otherwise, the conflict_type will depend on whether the
vacuum has removed the dead row. so, the conflict management system or
users would easily know when to rely on this update_missing conflict
type.

-- 
With Regards,
Amit Kapila.

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.