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

On Sat, Oct 7, 2023 at 3:46 AM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Fri, Oct 6, 2023 at 6:30 PM Hayato Kuroda (Fujitsu)
> >
> > Based on that, I added another binary function binary_upgrade_create_logical_replication_slot().
> > This function is similar to pg_create_logical_replication_slot(), but the
> > restart_lsn and confirmed_flush are set to *next* WAL segment. The pointed
> > filename is returned and it is passed to pg_resetwal command.
> >
>
> I am not sure if it is a good idea that a
> binary_upgrade_create_logical_replication_slot() API does the logfile
> name calculation.
>

The other problem is that pg_resetwal removes all pre-existing WAL
files which in this case could lead to the removal of the WAL file
corresponding to restart_lsn. This is because at least the shutdown
checkpoint record will be written after the creation of slots which
could be in the new file used for restart_lsn. Then when we invoke
pg_resetwal, it can remove that file.

One idea to deal with this could be to do the reset WAL stuff
(FindEndOfXLOG(), KillExistingXLOG(), KillExistingArchiveStatus(),
WriteEmptyXLOG()) in a separate function (say in pg_upgrade) and then
create slots. If we do this, then we additionally need an option in
pg_resetwal which skips resetting the WAL as that would have been done
before creating the slots.

--
With Regards,
Amit Kapila.