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From: Amit Kapila <amit.kapila16@gmail.com>
Date: Thu, 5 May 2022 09:42:32 +0530
Message-ID: 
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Subject: Re: Skipping schema changes in publication
To: Peter Eisentraut <peter.eisentraut@enterprisedb.com>
Cc: vignesh C <vignesh21@gmail.com>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
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On Thu, May 5, 2022 at 9:20 AM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Wed, May 4, 2022 at 7:05 PM Peter Eisentraut
> <peter.eisentraut@enterprisedb.com> wrote:
> >
> > On 14.04.22 15:47, Peter Eisentraut wrote:
> > > That said, I'm not sure this feature is worth the trouble.  If this is
> > > useful, what about "whole database except these schemas"?  What about
> > > "create this database from this template except these schemas".  This
> > > could get out of hand.  I think we should encourage users to group their
> > > object the way they want and not offer these complicated negative
> > > selection mechanisms.
> >
> > Another problem in general with this "all except these" way of
> > specifying things is that you need to track negative dependencies.
> >
> > For example, assume you can't add a table to a publication unless it has
> > a replica identity.  Now, if you have a publication p1 that says
> > includes "all tables except t1", you now have to check p1 whenever a new
> > table is created, even though the new table has no direct dependency
> > link with p1.  So in more general cases, you would have to check all
> > existing objects to see whether their specification is in conflict with
> > the new object being created.
> >
>
> Yes, I think we should avoid adding such negative dependencies. We
> have carefully avoided such dependencies during row filter, column
> list work where we don't try to perform DDL time verification.
> However, it is not clear to me how this proposal is related to this
> example or in general about tracking negative dependencies?
>

I mean to say that even if we have such a restriction, it would apply
to "for all tables" or other publications as well. In your example,
consider one wants to Alter a table and remove its replica identity,
we have to check whether the table is part of any publication similar
to what we are doing for relation persistence in
ATPrepChangePersistence.

> AFAIR, we
> currently have such a check while changing persistence of logged table
> (logged to unlogged, see ATPrepChangePersistence) where we cannot
> allow changing persistence if that relation is part of some
> publication. But as per my understanding, this feature shouldn't add
> any such new dependencies. I agree that we have to ensure that
> existing checks shouldn't break due to this feature.
>
> > Now publications don't actually work that way, so it's not a real
> > problem right now, but similar things could work like that.  So I think
> > it's worth thinking this through a bit.
> >
>
> This is a good point and I agree that we should be careful to not add
> some new negative dependencies unless it is really required but I
> can't see how this proposal will make it more prone to such checks.
>

-- 
With Regards,
Amit Kapila.