Horton

Re: Conflict detection for update_deleted in logical replication

shveta malik <shveta.malik@gmail.com>

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From: shveta malik <shveta.malik@gmail.com>
To: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>
Cc: vignesh C <vignesh21@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, Nisha Moond <nisha.moond412@gmail.com>, "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>, pgsql-hackers <pgsql-hackers@postgresql.org>, shveta malik <shveta.malik@gmail.com>
Date: 2025-04-25T10:35:51Z
Lists: pgsql-hackers 
>
> Here is V30 patch set includes the following changes:
>

Thank You for the patch, please find few concerns:

1)
By looking at code of ApplyLauncherMain(), it appears that we stopped
advancing shared-slot's xmin if any of the subscriptions with
retain_conflict_info is disabled. If a subscription is not being used
and is disabled forever (or for quite long), that means xmin will
never be advanced and we will keep accumulating dead-rows even if
other subscribers with retain_conflict_info are actively setting their
oldest_xmin. This could be problematic. Here too, there should be some
way to set stop-conflict-rettention for such a subscription like we do
for 'subscriber not able to catch-up case'.
But I understand it can be complex to implement as we do not know for
how long a subscription is disabled. If we do not find a simpler way
to implement it, then at least we can document  such cases and the
risks associated with disabled subscription which has
'retain_conflict_info' enabled. Thoughts?

2)
in wait_for_local_flush(), we have
should_stop_conflict_info_retention() before 'AllTablesyncsReady'
check. Should we give a discount for table-sync time and avoid doing
stop-conflict-retention when table-sync is going on? This is because
table-sync is one time operation (or done only on
subscription-refresh), so we shall not count time spent in table-sync
for 'max_conflict_retention_duration'. We can reset our timer if
table-sync is observed to be going on. Thoughts?

thanks
Shveta

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.