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

On Tue, Nov 28, 2023 at 10:58 PM Hayato Kuroda (Fujitsu)
<kuroda.hayato@fujitsu.com> wrote:
>
> 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.

I think PQgetvalue() returns an empty string if the result value is null.

Regards,

--
Masahiko Sawada
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