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From: Amit Kapila <amit.kapila16@gmail.com>
Date: Wed, 4 May 2022 09:44:53 +0530
Message-ID: 
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Subject: Re: Skipping schema changes in publication
To: Peter Smith <smithpb2250@gmail.com>
Cc: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>,
 vignesh C <vignesh21@gmail.com>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
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On Tue, May 3, 2022 at 2:24 PM Peter Smith <smithpb2250@gmail.com> wrote:
>
> On Thu, Apr 28, 2022 at 9:32 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> >
> ...
> > Another idea that occurred to me today for tables this is as follows:
> > 1. Allow to mention except during create publication ... For All Tables.
> > CREATE PUBLICATION pub1 FOR ALL TABLES EXCEPT TABLE t1,t2;
> > 2. Allow to Reset it. This new syntax will reset all objects in the
> > publications.
> > Alter Publication ... RESET;
> > 3. Allow to add it to an existing publication
> > Alter Publication ... Add ALL TABLES [EXCEPT TABLE t1,t2];
> >
> > I think it can be extended in a similar way for schema syntax as well.
> >
>
> Consider if the user does
> CREATE PUBLICATION pub1 FOR ALL TABLES EXCEPT TABLE t1,t2;
> ALTER PUBLICATION pub1 ADD ALL TABLES EXCEPT t3,t4;
>
> What does it mean?
> e.g. Is there only one exception list that is modified? Or did the ADD
> ALL TABLES override all meaning of the original list?
> e.g. Are we now skipping t1,t2,t3,t4, or are we now only skipping t3,t4?
>

This won't be allowed. We won't allow changing ALL TABLES publication
unless the user first performs RESET. This is the purpose of providing
the RESET variant.

> ~~~
>
> Here is a similar example, where the ADD TABLE seems confusing to me
> when it intersects with a prior EXCEPT
> e.g.
> CREATE PUBLICATION pub1 FOR ALL TABLES EXCEPT t1,t2; // ok
> ALTER PUBLICATION pub1 ADD TABLE t1; ???
>
> What does it mean?
> e.g. Does the explicit ADD TABLE override the original exception list?
> e.g. Is t1 published now or should that ALTER have caused an error?
>

This won't be allowed either. We don't allow to Add/Drop from All
Tables publication unless the user performs a RESET. This is true even
today except that we don't have a RESET syntax.

> ~~
>
> It feels like there are too many tricky rules when using EXCEPT with
> ALTER PUBLICATION. I guess complexities can be described in the
> documentation but IMO it would be better if the ALTER syntax could be
> unambiguous in the first place.
>

Agreed.

> So perhaps the rules should be more
> restrictive (e.g. just disallow ALTER ... ADD any table that overlaps
> the existing EXCEPT list ??)
>

I think the current proposal seems to be restrictive enough to avoid
any tricky issues. Do you see any other problem?


-- 
With Regards,
Amit Kapila.