Horton

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

shveta malik <shveta.malik@gmail.com>

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From: shveta malik <shveta.malik@gmail.com>
To: Ajin Cherian <itsajin@gmail.com>
Cc: Japin Li <japinli@hotmail.com>, Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>, Ashutosh Sharma <ashu.coek88@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>, PostgreSQL mailing lists <pgsql-hackers@postgresql.org>, shveta malik <shveta.malik@gmail.com>
Date: 2025-10-31T05:34:31Z
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. Enhance slot synchronization API to respect promotion signal.

  2. Fix inconsistent elevel in pg_sync_replication_slots() retry logic.

  3. Refactor slot synchronization logic in slotsync.c.

  4. Fix intermittent BF failure in 040_standby_failover_slots_sync.

  5. Add retry logic to pg_sync_replication_slots().

  6. Fix LOCK_TIMEOUT handling in slotsync worker.

  7. Add slotsync skip statistics.

On Thu, Oct 30, 2025 at 3:48 PM Ajin Cherian <itsajin@gmail.com> wrote:
>
>
> Thanks for your review, Japin. Here's patch v20 addressing the comments.
>

Thank You for the patch. Please find a few comment son test:


1)
+# until the slot becomes sync-ready (when the standby catches up to the
+# slot's restart_lsn).

I think it should be 'when the primary server catches up' or 'when the
remote slot catches up with the locally reserved position.'

2)
+# Attempt to synchronize slots using API. This will initially fail because
+# the slot is not yet sync-ready (standby hasn't caught up to slot's
restart_lsn),
+# but the API will wait and retry. Call the API in a background process.

a)
'This will initially fail ' seems like the API will give an error,
which is not the case

b) 'standby hasn't caught up to slot's restart_lsn' is not correct.

We can rephrase to:
# Attempt to synchronize slots using the API. The API will continue
retrying synchronization until the remote slot catches up with the
locally reserved position.

3)
+# Enable the Subscription, so that the slot catches up

slot --> remote slot

4)
+# Create xl_running_xacts records on the primary for which the
standby is waiting

Shall we rephrase to below or anything better if you have?:
Create xl_running_xacts on the primary to speed up restart_lsn advancement.

5)
+# Confirm that the logical failover slot is created on the standby and is
+# flagged as 'synced'

Suggestion:
Verify that the logical failover slot is created on the standby,
marked as 'synced', and persisted.

(It is important to mention persisted because even temporary slot is
marked as synced)

thanks
Shveta