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

Dear Shlok,

> 
> I have tested the above scenario. We are able to override the
> max_slot_wal_keep_size by using  '--new-options  "-c
> max_slot_wal_keep_size=val"'. And also with some insert statements
> during pg_upgrade, old WAL file were deleted and logical replication
> slots were invalidated. Since the slots were invalidated replication
> was not happening after the upgrade.

Yeah, theoretically it could be overwritten, but I still think we do not have to
guard. Also, connections must not be established during the upgrade [1].
I improved the ereport() message in the new patch[2]. How do you think?

[1]: https://www.postgresql.org/message-id/ZNZ4AxUMIrnMgRbo%40momjian.us
[2]:
https://www.postgresql.org/message-id/TYCPR01MB587007EA2F9AB92F0E1F5957F5D4A%40TYCPR01MB5870.jpnprd01.prod.outlook.com

Best Regards,
Hayato Kuroda
FUJITSU LIMITED