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

On Thu, Aug 8, 2024 at 3:41 PM Zhijie Hou (Fujitsu)
<houzj(dot)fnst(at)fujitsu(dot)com> wrote:
>
> On Thursday, August 8, 2024 6:01 PM shveta malik <shveta(dot)malik(at)gmail(dot)com> wrote:
> >
> > On Thu, Aug 8, 2024 at 12:03 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
> > wrote:
> > >
> > > On Thu, Aug 8, 2024 at 10:37 AM Hayato Kuroda (Fujitsu)
> > > <kuroda(dot)hayato(at)fujitsu(dot)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?
>
> I think this is a general issue that can occur not only due to 2PC. IIUC, this
> problem should arise if any ERROR arises after setting the
> replorigin_session_origin_lsn but before the CommitTransactionCommand is
> completed. If so, I think we should register it for tablesync worker as well.
>

As pointed out earlier, won't using PG_ENSURE_ERROR_CLEANUP() instead
of PG_CATCH() be enough?

--
With Regards,
Amit Kapila.