Re: Skipping logical replication transactions on subscriber side

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.

BTW how useful is specifying LSN instead of XID in practice? Given
that this skipping behavior is used to skip the particular transaction
(or its part of operations) in question, I’m not sure specifying LSN
or time is useful. And, if it’s essentially the same as
pg_replication_origin_advance(), we don’t need to have it.

> The basic idea is that I am trying to use options here rather than a
> keyword-based syntax as there can be multiple such options.

Agreed.

Regards,

--
Masahiko Sawada
EDB: https://www.enterprisedb.com/