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In-Reply-To: <4f4867da-f581-0330-974f-da9031ac3e1c@enterprisedb.com>
From: Amit Kapila <amit.kapila16@gmail.com>
Date: Thu, 5 May 2022 09:20:36 +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 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? 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.