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

Dear Amit,

> So, we have three options here (a) As you have done in the patch,
> document this limitation and request user to perform some manual steps
> to drop the subscription; (b) don't allow upgrade to proceed if there
> are invalid slots in the old cluster; (c) provide a new function like
> pg_copy_logical_replication_slot_contents() where we copy the required
> contents like invalid status(ReplicationSlotInvalidationCause), etc.
>
> Personally, I would prefer (b) because it will minimize the steps
> required to perform by the user after the upgrade and looks cleaner
> solution.
>
> Thoughts?

Thanks for suggestion. I agreed (b) was better because it did not endanger users
for data lost. I implemented locally and worked well, so I'm planning to adopt
the idea in next version, if no objections.

Best Regards,
Hayato Kuroda
FUJITSU LIMITED