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

On Sat, Oct 14, 2023 at 10:45 AM Hayato Kuroda (Fujitsu)
<kuroda(dot)hayato(at)fujitsu(dot)com> wrote:
>
> Here is a new patch.
>
> Previously I wrote:
> > Based on above idea, I made new version patch which some functionalities were
> > exported from pg_resetwal. In this approach, pg_upgrade itself removed WALs and
> > then create logical slots, then pg_resetwal would be called with new option
> > --no-switch, which avoid to switch a WAL segment file. The option is only used
> > for the upgrading purpose so it is not written in doc and usage(). This option
> > is not required if pg_resetwal -o does not discard WAL records. Please see the
> > fork thread [1].
>
> But for now, these changes were reverted because changing pg_resetwal -o stuff
> may be a bit risky. This has been located more than ten years so that we should
> be more careful for modifying.
> Also, I cannot come up with problems if slots are created after the pg_resetwal.
> Background processes would not generate decodable changes (listed in [1]), and
> BGworkers by extensions could be ignored [2].
> Based on the discussion on forked thread [3] and if it is accepted, we will apply
> again.
>

Yeah, I think introducing additional complexity unless it is really
required sounds a bit scary to me as well. BTW, please find attached
some cosmetic changes.

One minor additional comment:
+# Initialize subscriber cluster
+my $subscriber = PostgreSQL::Test::Cluster->new('subscriber');
+$subscriber->init(allows_streaming => 'logical');

Why do we need to set wal_level as logical for subscribers?

--
With Regards,
Amit Kapila.