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From: Peter Smith <[email protected]>
To: shveta malik <[email protected]>
Cc: vignesh C <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Subject: Re: Logical Replication - revisit `is_table_publication` function implementation
Date: Wed, 8 Apr 2026 16:04:45 +1000
Message-ID: <CAHut+PtfHzxHFkHJWYoxOFpgpSH5HNAGmP5sSrwh1d+R0Ab-BQ@mail.gmail.com> (raw)
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On Wed, Apr 8, 2026 at 3:25 PM shveta malik <[email protected]> wrote:
>
> On Wed, Apr 8, 2026 at 10:24 AM Peter Smith <[email protected]> wrote:
> >
> > On Wed, Apr 8, 2026 at 1:45 PM vignesh C <[email protected]> wrote:
> > >
> > > On Tue, 7 Apr 2026 at 12:32, Peter Smith <[email protected]> wrote:
> > > >
> > > > Hi, after confirming my understanding of pg_publication_rel [1], I
> > > > revisited some logical replication internal functions.
> > > >
> > > > Specifically.
> > > > * The `is_table_publication` function is for checking if the
> > > > publication has a clause like "FOR TABLE t1".
> > > > * The `is_schema_publication` function is for checking if the
> > > > publication has a clause like "FOR TABLES IN SCHEMA s1".
> > > >
> > > > Notice that neither of these ("FOR TABLE", "FOR TABLES IN SCHEMA")
> > > > clauses are possible simultaneously with "FOR ALL TABLES".
> > > >
> > > > And we can readily discover if "FOR ALL TABLES" (aka `puballtables`)
> > > > is present from the pubform.
> > > >
> > > > We can use this to optimise and simplify the implementations of the
> > > > `is_schema_publication` and `is_table_publication` functions.
> > > >
> > > > PSA patch v1.
> > > >
> > > > AFAICT, the result is:
> > > > - less code + simpler logic. e.g. is_table_publication does not check
> > > > 'prexcept' anymore
> > > > - more efficient. e.g. skips unnecessary scanning when puballtables is true.
> > > > - more consistent. e.g., both functions are now almost identical.
> > > >
> > > > Thoughts?
> > >
> >
> > Hi Vignesh. Thanks for reviewing!
> >
> > > I'm not sure if this additional check is sufficient in case of
> > > is_schema_publication. Checking only puballtables can exclude FOR ALL
> > > TABLES, but it still cannot distinguish regular table publications,
> > > empty publications, or sequence publications. In all of those cases,
> > > we still need to check pg_publication_namespace.
> >
> > Yes, this condition is only an optimisation for FOR ALL TABLES, as the
> > comment says.
> >
> > IMO, the overhead of 1 additional boolean check for cases where it
> > doesn't help is an insignificant trade-off for the savings when it can
> > return false.
> >
> > > And also why just check for puballtables why not to check for puballsequences
> >
> > I think function is_schema_publication() is unrelated to 'puballsequences'.
> >
> > e.g. all the following will still need to check
> > pg_publication_namespace, regardless of the 'puballsequences' value.
> >
> > ex1. CREATE PUBLICATION ... FOR ALL SEQUENCES;
> > ex2. CREATE PUBLICATION ... FOR ALL SEQUENCES, FOR TABLES IN SCHEMA s1;
> > ex3. CREATE PUBLICATION ... FOR TABLES IN SCHEMA s1;
> >
>
> IIUC, we don't support mix of ALL SEQUENCES and TABLES IN SCHEMA s1.
> So I could not understand your point, why FOR ALL SEQ still need to
> check pg_publication_namespace?
>

Oh! You are right.

(Sorry, Vignesh, I did not recognise that combination as unsupported).

I'll post a patch update to handle it.

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

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