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From: Peter Smith <smithpb2250@gmail.com>
Date: Mon, 7 Mar 2022 17:14:48 +1100
Message-ID: <CAHut+PtRxiQR_4UFLNThg-NNRV447FvwtcR-BvqMzjyMJXKwfw@mail.gmail.com>
Subject: Re: Handle infinite recursion in logical replication setup
To: vignesh C <vignesh21@gmail.com>
Cc: "kuroda.hayato@fujitsu.com" <kuroda.hayato@fujitsu.com>, 
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
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On Mon, Mar 7, 2022 at 4:20 PM vignesh C <vignesh21@gmail.com> wrote:
>
> On Mon, Mar 7, 2022 at 10:26 AM Peter Smith <smithpb2250@gmail.com> wrote:
> >
> > Hi Vignesh, I also have not looked at the patch yet, but I have what
> > seems like a very fundamental (and possibly dumb) question...
> >
> > Basically, I do not understand the choice of syntax for setting things up.
> >
> > IMO that "only-local" option sounds very similar to the other
> > PUBLICATION ("publish") options which decide the kinds of things that
> > will be published. So it feels more natural for me to think of the
> > publisher as being the one to decide what will be published.
> >
> > e.g.
> >
> > option 1:
> > CREATE PUBLICATION p1 FOR TABLE t1;
> > CREATE SUBSCRITION s1 ... FOR PUBLICATION p1 WITH (only_local = true);
> >
> > option 2:
> > CREATE PUBLICATION p1 FOR TABLE t1 WEHRE (publish = 'only_local');
> > CREATE SUBSCRITION s1 ... FOR PUBLICATION p1;
> >
> > ~~
> >
> > IIUC the patch is using option 1. My first impression was it feels
> > back-to-front for the SUBSCRIPTION telling the PUBLICATION what to
> > publish.
> >
> > So, why does the patch use syntax option 1?
>
> I felt the advantage with keeping it at the subscription side is that,
> the subscriber from one node can subscribe with only_local option on
> and a different subscriber from a different node can subscribe with
> only_local option as off. This might not be possible with having the
> option at publisher side. Having it at the subscriber side might give
> more flexibility for the user.
>

OK.  Option 2 needs two publications for that scenario. IMO it's more
intuitive this way, but maybe you wanted to avoid the extra
publications?

node0:
CREATE PUBLICATION p1 FOR TABLE t1;
CREATE PUBLICATION p1_local FOR TABLE t1 WITH (publish = 'only_local');

node1: CREATE SUBSCRIPTION s1 ... FOR PUBLICATION p1_local;
node2: CREATE SUBSCRIPTION s1 ... FOR PUBLICATION p1;

------
Kind Regards,
Peter Smith.
Fujitsu Australia