Re: Skipping logical replication transactions on subscriber side

On Tue, Dec 14, 2021 at 3:41 PM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
>
> On Tue, Dec 14, 2021 at 2:36 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> >
> > > >
> > > > I agree with this theory. Can we reflect this in comments so that in
> > > > the future we know why we didn't pursue this direction?
> > >
> > > I might be missing something here, but for streaming, transaction
> > > users can decide whether they wants to skip or not only once we start
> > > applying no? I mean only once we start applying the changes we can
> > > get some errors and by that time we must be having all the changes for
> > > the transaction.
> > >
> >
> > That is right and as per my understanding, the patch is trying to
> > accomplish the same.
> >
> > > So I do not understand the point we are trying to
> > > discuss here?
> > >
> >
> > The point is that whether we can skip the changes while streaming
> > itself like when we get the changes and write to a stream file. Now,
> > it is possible that streams from multiple transactions can be
> > interleaved and users can change the skip_xid in between. It is not
> > that we can't handle this but that would require a more complex design
> > and it doesn't seem worth it because we can anyway skip the changes
> > while applying as you mentioned in the previous paragraph.
>
> Actually, I was trying to understand the use case for skipping while
> streaming. Actually, during streaming we are not doing any database
> operation that means this will not generate any error.
>

Say, there is an error the first time when we start to apply changes
for such a transaction. So, such a transaction will be streamed again.
Say, the user has set the skip_xid before we stream a second time, so
this time, we can skip it either during the stream phase or apply
phase. I think the patch is skipping it during apply phase.
Sawada-San, please confirm if my understanding is correct?

--
With Regards,
Amit Kapila.