Re: Synchronizing slots from primary to standby - Mailing list pgsql-hackers

On Mon, Apr 1, 2024 at 10:40 AM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> After this step and before the next, did you ensure that the slot sync
> has synced the latest confirmed_flush/restart LSNs? You can query:
> "select slot_name,restart_lsn, confirmed_flush_lsn from
> pg_replication_slots;" to ensure the same on both the primary and
> standby.

Yes, after ensuring the slot is synced on the standby, the problem is
reproduced for me and the proposed patch fixes it (i.e. able to see
the changes even after the promotion). I'm just thinking if we can add
a TAP test for this issue, but one key aspect of this reproducer is to
not let someone write a RUNNING_XACTS WAL record on the primary in
between before the standby promotion. Setting bgwriter_delay to max
isn't helping me. I think we can think of using an injection point to
add delay in LogStandbySnapshot() for having this problem reproduced
consistently in a TAP test. Perhaps, we can think of adding this later
after the fix is shipped.

--
Bharath Rupireddy
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com