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From: Peter Smith <smithpb2250@gmail.com>
Date: Tue, 3 May 2022 18:54:33 +1000
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Subject: Re: Skipping schema changes in publication
To: Amit Kapila <amit.kapila16@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 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?

~~~

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?

~~

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

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