Re: Skipping logical replication transactions on subscriber side

On Wed, Oct 27, 2021 at 8:32 AM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
>
> On Tue, Oct 26, 2021 at 7:29 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> >
> > On Tue, Oct 26, 2021 at 2:27 PM Greg Nancarrow <gregn4422(at)gmail(dot)com> wrote:
> > >
> > > On Tue, Oct 26, 2021 at 5:16 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> > > >
> > > > I agree that we will need a separate syntax for conflict resolution
> > > > but there is some similarity in what I proposed above (On
> > > > Error/Conflict [1]) with the existing syntax of Insert ... On
> > > > Conflict. I understand that here the context is different and we are
> > > > storing this information in the catalog but still there is some syntax
> > > > similarity and it will avoid adding new syntax variants.
> > > >
> > >
> > > The problem I see with the suggested syntax:
> > >
> > > Alter Subscription <sub_name> On Error ( subscription_parameter [=
> > > value] [, ... ] );
> > > OR
> > > Alter Subscription <sub_name> On Conflict ( subscription_parameter [=
> > > value] [, ... ] );
> > >
> > > is that "On Error ..." and "On Conflict" imply an action to be done on
> > > a future condition (Error/Conflict), whereas at least in this case
> > > (skip_xid) it's only AFTER the problem condition has occurred that we
> > > know the XID of the failed transaction that we want to skip. So that
> > > syntax looks a little confusing to me. Unless you had something else
> > > in mind on how it would work?
> > >
> >
> > You have a point. The other alternatives on this line could be:
> >
> > Alter Subscription <sub_name> SKIP ( subscription_parameter [=value] [, ... ] );
> >
> > where subscription_parameter can be one of:
> > xid = <xid_val>
> > lsn = <lsn_val>
> > ...
>
> Looks better.
>

If we want to follow the above, then how do we allow users to reset
the parameter? One way is to allow the user to set xid as 0 which
would mean that we reset it. The other way is to allow SET/RESET
before SKIP but not sure if that is a good option. I was also thinking
about how we can extend the current syntax in the future if we want to
allow users to specify multiple xids? I guess we can either make xid
as a list or allow it to be specified multiple times. We don't need to
do this now but just from the point that we should be able to extend
it later if required.

--
With Regards,
Amit Kapila.