Re: [bug fix] prepared transaction might be lost when max_prepared_transactions is zero on the subscriber

On Thu, Aug 8, 2024 at 12:03 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Thu, Aug 8, 2024 at 10:37 AM Hayato Kuroda (Fujitsu)
> <kuroda.hayato@fujitsu.com> wrote:
> >
> ...
> >
> > An easiest fix is to reset session replication origin before calling the
> > RecordTransactionAbort(). I think this can happen when 1) LogicalRepApplyLoop()
> > raises an ERROR or 2) apply worker exits. Attached patch can fix the issue on HEAD.
> >
>
> Few comments:
> =============
> *
> @@ -4409,6 +4409,14 @@ start_apply(XLogRecPtr origin_startpos)
>   }
>   PG_CATCH();
>   {
> + /*
> + * Reset the origin data to prevent the advancement of origin progress
> + * if the transaction failed to apply.
> + */
> + replorigin_session_origin = InvalidRepOriginId;
> + replorigin_session_origin_lsn = InvalidXLogRecPtr;
> + replorigin_session_origin_timestamp = 0;
>
> Can't we call replorigin_reset() instead here?
>
> *
> + /*
> + * Register a callback to reset the origin state before aborting the
> + * transaction in ShutdownPostgres(). This is to prevent the advancement
> + * of origin progress if the transaction failed to apply.
> + */
> + before_shmem_exit(replorigin_reset, (Datum) 0);
>
> I think we need this despite resetting the origin-related variables in
> PG_CATCH block to handle FATAL error cases, right? If so, can we use
> PG_ENSURE_ERROR_CLEANUP() instead of PG_CATCH()?

+1

Basic tests work fine on this patch. Just thinking out loud,
SetupApplyOrSyncWorker() is called for table-sync worker as well and
IIUC tablesync worker does not deal with 2PC txns. So do we even need
to register replorigin_reset() for tablesync worker as well? If we may
hit such an issue in general, then perhaps we need it in table-sync
worker  otherwise not.  It needs some investigation. Thoughts?

thanks
Shveta