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

Dear Sawada-san,

> On Tue, Nov 28, 2023 at 7:04 PM Hayato Kuroda (Fujitsu)
> <kuroda.hayato@fujitsu.com> wrote:
> >
> >
> > Yeah, we followed binary_upgrade_create_empty_extension(). Also, we set as
> > un-strict to keep a caller function simpler.
> >
> > Currently get_old_cluster_logical_slot_infos() executes a query and it contains
> > binary_upgrade_logical_slot_has_caught_up(). In pg_upgrade layer, we
> assumed
> > either true or false is returned.
> >
> > But if proisstrict is changed true, we must handle the case when NULL is
> returned.
> > It is small but backseat operation.
> 
> Which cases are you concerned pg_upgrade could pass NULL to
> binary_upgrade_logical_slot_has_caught_up()?

Actually, we do not expect that it won't input NULL. IIUC all of slots have
slot_name, and subquery uses its name. But will it be kept forever? I think we
can avoid any risk.

> I've not tested it yet but even if it returns NULL, perhaps
> get_old_cluster_logical_slot_infos() would still set curr->caught_up
> to false, no?

Hmm. I checked the C99 specification [1] of strcmp, but it does not define the
case when the NULL is input. So it depends implementation.

[1]: https://www.dii.uchile.cl/~daespino/files/Iso_C_1999_definition.pdf

Best Regards,
Hayato Kuroda
FUJITSU LIMITED