Re: Handle infinite recursion in logical replication setup

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From: vignesh C <[email protected]>
To: Peter Smith <[email protected]>
Cc: [email protected] <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Subject: Re: Handle infinite recursion in logical replication setup
Date: Mon, 7 Mar 2022 12:47:43 +0530
Message-ID: <CALDaNm2ttHxORgvtzd3ZFZe7-uLjfrAX3WSM-Wxf5Et_CVm41Q@mail.gmail.com> (raw)
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On Mon, Mar 7, 2022 at 11:45 AM Peter Smith <[email protected]> wrote:
>
> On Mon, Mar 7, 2022 at 4:20 PM vignesh C <[email protected]> wrote:
> >
> > On Mon, Mar 7, 2022 at 10:26 AM Peter Smith <[email protected]> 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?

Yes, I wanted to avoid the extra publication creation that you pointed
out. Option 1 can handle this scenario without creating the extra
publications:
node0: CREATE PUBLICATION p1 FOR TABLE t1;
node1: CREATE SUBSCRIPTION s1 ... FOR PUBLICATION p1 with (only_local = on);
node2:  CREATE SUBSCRIPTION s1 ... FOR PUBLICATION p1 with (only_local = off);

I'm ok with both the approaches, now that this scenario can be handled
by using both the options. i.e providing only_local option as an
option while creating publication or providing only_local option as an
option while creating subscription as Peter has pointed out at [1].
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 WITH (publish = 'only_local');
CREATE SUBSCRITION s1 ... FOR PUBLICATION p1;

Shall we get a few opinions on this and take it in that direction?

[1] - https://www.postgresql.org/message-id/CAHut%2BPsAWaETh9VMymbBfMrqiE1KuqMq%2BwpBg0s7eMzwLATr%2Bw%40ma...

Regards,
Vignesh

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