Re: [PoC] pg_upgrade: allow to upgrade publisher node

On Fri, Apr 07, 2023 at 12:51:51PM +0000, Hayato Kuroda (Fujitsu) wrote:
> Dear Julien,
>
> > > Agreed, but then shouldn't the option be named "--logical-slots-only" or
> > > something like that, same for all internal function names?
> >
> > Seems right. Will be fixed in next version. Maybe
> > "--logical-replication-slots-only"
> > will be used, per Peter's suggestion [1].
>
> After considering more, I decided not to include the word "logical" in the option
> at this point. This is because we have not decided yet whether we dumps physical
> replication slots or not. Current restriction has been occurred because of just
> lack of analysis and considerations, If we decide not to do that, then they will
> be renamed accordingly.

Well, even if physical replication slots were eventually preserved during
pg_upgrade, maybe users would like to only keep one kind of the others so
having both options could make sense.

That being said, I have a hard time believing that we could actually preserve
physical replication slots. I don't think that pg_upgrade final state is fully
reproducible: not all object oids are preserved, and the various pg_restore
are run in parallel so you're very likely to end up with small physical
differences that would be incompatible with physical replication. Even if we
could make it totally reproducible, it would probably be at the cost of making
pg_upgrade orders of magnitude slower. And since many people are already
complaining that it's too slow, that doesn't seem like something we would want.