Re: Support logical replication of DDLs

On Mon, Feb 20, 2023 at 3:23 AM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
>
> On Fri, Feb 17, 2023 at 1:13 PM Zheng Li <zhengli10(at)gmail(dot)com> wrote:
> >
> > > > I've implemented a prototype to allow replicated objects to have the
> > > > same owner from the publisher in
> > > > v69-0008-Allow-replicated-objects-to-have-the-same-owner-from.patch.
> > > >
> > >
> > > I also think it would be a helpful addition for users.A few points
> > Thanks for supporting this addition.
> >
> > > that come to my mind are: (a) Shouldn't the role have the same
> > > privileges (for ex. rolbypassrls or rolsuper) on both sides before we
> > > allow this? (b) Isn't it better to first have a replication of roles?
> >
> > > I think if we have (b) then it would be probably a bit easier because
> > > if the subscription has allowed replicating roles and we can confirm
> > > that the role is replicated then we don't need to worry about the
> > > differences.
> >
> > Yes, having role replication will help further reduce the manual
> > effort. But even if we don't end up doing role replication soon, I
> > think we can still provide this subscription option (match_ddl_owner,
> > off by default) and document that the same roles need to be on both
> > sides for it to work.
>
> From the user perspective, I expect that the replicated objects are
> created on the subscriber by the same owner as the publisher, by
> default.

OK, I agree. I think the use cases for matching the owner are likely
more than the other way around. I can make the subscription option
"match_ddl_owner" on by default in the next version.

> I think that the same name users must exist on both sides (by
> role replication or manually if not supported yet) but the privileges
> of the role doesn't necessarily need to match. IOW, it's sufficient
> that the role on the subscriber has enough privileges to create the
> object.

This is also my understanding.

> > > Now, coming to implementation, won't it be better if we avoid sending
> > > the owner to the subscriber unless it is changed for the replicated
> > > command? Consider the current case of tables where we send schema only
> > > if it is changed. This is not a direct mapping but it would be better
> > > to avoid sending additional information and then process it on the
> > > subscriber for each command.
> >
> > Right, we can do some optimization here: only send the owner for
> > commands that create objects (CREATE TABLE/FUNCTION/INDEX etc.) Note
> > that ALTER TABLE/OBJECT OWNER TO is replicated so we don't need to
> > worry about owner change.
>
> What role will be used for executing ALTER and DROP commands on the
> subscriber? the subscription owner?

Yes, I think DROP and ALTER commands (and other non-CREATE commands)
can be executed by the subscription owner (superuser).

Regards,
Zane