Re: Support logical replication of DDLs

On Wed, Apr 26, 2023 at 10:01 AM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
>
> On Tue, Apr 25, 2023 at 12:58 PM Zhijie Hou (Fujitsu)
> <houzj(dot)fnst(at)fujitsu(dot)com> wrote:
> >
> > Aport from above comments, I splitted the code related to verbose
> > mode to a separate patch. And here is the new version patch set.
> >
>
> As for DDL replication, we create event triggers to write deparsed DDL
> commands to WAL when creating a publication with the ddl option. The
> event triggers are recreated/dropped at ALTER/DROP PUBLICATION. I'm
> concerned it's possible that DDLs executed while such a publication
> not existing are not replicated. For example, imagine the following
> steps,
>
> 1. CREATE PUBLICATION test_pub ... WITH (ddl = 'table);
> 2. CREATE SUBSCRIPTION test_sub ... PUBLICATION test_pub;
> 3. ALTER SUBSCRIPTION test_sub DISABLE;
> 4. DROP PUBLICATION test_pub;
> 5. CREATE PUBLICATION test_pub ... WITH (ddl = 'table);
> 6. ALTER SUBSCRIPTION test_sub ENABLE;
>
> DDLs executed between 4 and 5 won't be replicated.
>

But we won't even send any DMLs between 4 and 5. In fact, WALSender
will give an error for those DMLs that publication doesn't exist as it
uses a historic snapshot. So, why do we expect DDLs between Drop and
Create of publication should be replicated?

--
With Regards,
Amit Kapila.