Re: Improve pg_sync_replication_slots() to wait for primary to advance

Ajin Cherian <itsajin@gmail.com>

From: Ajin Cherian <itsajin@gmail.com>

To: Amit Kapila <amit.kapila16@gmail.com>

Cc: shveta malik <shveta.malik@gmail.com>, PostgreSQL mailing lists <pgsql-hackers@postgresql.org>

Date: 2025-08-06T02:05:11Z

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Enhance slot synchronization API to respect promotion signal.
- 4bed04d39566 17.10 landed
- 94efd308bcec 18.4 landed
- 1362bc33e025 19 (unreleased) landed
Fix inconsistent elevel in pg_sync_replication_slots() retry logic.
- f1ddaa15357f 19 (unreleased) landed
Refactor slot synchronization logic in slotsync.c.
- 788ec96d591d 19 (unreleased) landed
Fix intermittent BF failure in 040_standby_failover_slots_sync.
- b47c50e5667b 19 (unreleased) landed
Add retry logic to pg_sync_replication_slots().
- 0d2d4a0ec3ec 19 (unreleased) landed
Fix LOCK_TIMEOUT handling in slotsync worker.
- 04396eacd3fa 19 (unreleased) cited
Add slotsync skip statistics.
- 76b78721ca49 19 (unreleased) cited

On Tue, Aug 5, 2025 at 4:22 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Tue, Aug 5, 2025 at 9:28 AM shveta malik <shveta.malik@gmail.com> wrote:
> >
> > On Mon, Aug 4, 2025 at 3:41 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> > >
> > > On Mon, Aug 4, 2025 at 12:19 PM shveta malik <shveta.malik@gmail.com> wrote:
> >
> > If we want to avoid continuously syncing newly added slots in later
> > cycles and instead focus only on the ones that failed to sync during
> > the first attempt, one approach is to maintain a list of failed slots
> > from the initial cycle and only retry those in subsequent attempts.
> > But this will add complexity to the implementation.
> >
>
> There will be some additional code for this but overall it improves
> the code in the lower level functions. We may want to use the existing
> remote_slot list for this purpose.
>
> The current proposed change in low-level functions appears to be
> difficult to maintain, especially the change proposed in
> update_and_persist_local_synced_slot(). If we can find a better way to
> achieve the same then we can consider the current approach as well.
>

Next patch, I'll work on addressing this comment. I'll need to
restructure the code to make this happen.

regards,
Ajin Cherian
Fujitsu Australia