Re: Skipping logical replication transactions on subscriber side

On Wed, Dec 15, 2021 at 8:19 AM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
>
> On Tue, Dec 14, 2021 at 2:35 PM Greg Nancarrow <gregn4422(at)gmail(dot)com> wrote:
> >
> > On Tue, Dec 14, 2021 at 3:23 PM vignesh C <vignesh21(at)gmail(dot)com> wrote:
> > >
> > > While the worker is skipping one of the skip transactions specified by
> > > the user and immediately if the user specifies another skip
> > > transaction while the skipping of the transaction is in progress this
> > > new value will be reset by the worker while clearing the skip xid. I
> > > felt once the worker has identified the skip xid and is about to skip
> > > the xid, the worker can acquire a lock to prevent concurrency issues:
> >
> > That's a good point.
> > If only the last_error_xid could be skipped, then this wouldn't be an
> > issue, right?
> > If a different xid to skip is specified while the worker is currently
> > skipping a transaction, should that even be allowed?
> >
>
> We don't expect such usage but yes, it could happen and seems not
> good. I thought we can acquire Share lock on pg_subscription during
> the skip but not sure it's a good idea. It would be better if we can
> find a way to allow users to specify only XID that has failed.
>

Yeah, but as we don't have a definite way to allow specifying only
failed XID, I think it is better to use share lock on that particular
subscription. We are already using it for add/update rel state (see,
AddSubscriptionRelState, UpdateSubscriptionRelState), so this will be
another place to use a similar technique.

--
With Regards,
Amit Kapila.