Re: Pgoutput not capturing the generated columns

On Mon, Sep 16, 2024 at 8:09 PM Peter Smith <smithpb2250@gmail.com> wrote:
>
> I thought that the option "publish_generated_columns" is more related
> to "column lists" than "row filters".
>
> Let's say table 't1' has columns 'a', 'b', 'c', 'gen1', 'gen2'.
>

> And
> PUBLICATION pub2 FOR TABLE t1 WITH (publish_generated_columns = false);
> is equivalent to
> PUBLICATION pub2 FOR TABLE t1(a,b,c);

This makes sense to me as it preserves the current behavior.

> Then:
> PUBLICATION pub1 FOR TABLE t1 WITH (publish_generated_columns = true);
> is equivalent to
> PUBLICATION pub1 FOR TABLE t1(a,b,c,gen1,gen2);

This also makes sense. It would also include future generated columns.

> So, I would expect this to fail because the SUBSCRIPTION docs say
> "Subscriptions having several publications in which the same table has
> been published with different column lists are not supported."

So I agree that it would raise an error if users subscribe to both
pub1 and pub2.

And looking back at your examples,

> > > e.g.1
> > > -----
> > > CREATE PUBLICATION pub1 FOR TABLE t1 WITH (publish_generated_columns = true);
> > > CREATE PUBLICATION pub2 FOR TABLE t1 WITH (publish_generated_columns = false);
> > > CREATE SUBSCRIPTION sub ... PUBLICATIONS pub1,pub2;
> > > -----
> > >
> > > e.g.2
> > > -----
> > > CREATE PUBLICATION pub1 FOR ALL TABLES WITH (publish_generated_columns = true);
> > > CREATE PUBLICATION pub2 FOR TABLE t1 WITH (publish_generated_columns = false);
> > > CREATE SUBSCRIPTION sub ... PUBLICATIONS pub1,pub2;
> > > -----

Both examples would not be supported.

> > >
> > > The CREATE SUBSCRIPTION docs [1] only says "Subscriptions having
> > > several publications in which the same table has been published with
> > > different column lists are not supported."
> > >
> > > Perhaps the user is supposed to deduce that the example above would
> > > work OK if table 't1' has no generated cols. OTOH, if it did have
> > > generated cols then the PUBLICATION column lists must be different and
> > > therefore it is "not supported" (??).
> >
> > With the patch, how should this feature work when users specify a
> > generated column to the column list and set publish_generated_column =
> > false, in the first place? raise an error (as we do today)? or always
> > send NULL?
>
> For this scenario, I suggested (see [1] #3) that the code could give a
> WARNING. As I wrote up-thread: This combination doesn't seem
> like something a user would do intentionally, so just silently
> ignoring it (which the current patch does) is likely going to give
> someone unexpected results/grief.

It gives a WARNING, and then publishes the specified generated column
data (even if publish_generated_column = false)? If so, it would mean
that specifying the generated column to the column list means to
publish its data regardless of the publish_generated_column parameter
value.

Regards,

-- 
Masahiko Sawada
Amazon Web Services: https://aws.amazon.com