Re: pg_upgrade and logical replication

On Wed, Sep 20, 2023 at 09:38:56AM +0900, Michael Paquier wrote:
> And this code path is used to start postmaster instances for old and
> new clusters. So it seems to me that it is incorrect if this is not
> conditional based on the cluster version.

Avoiding the startup of bgworkers during pg_upgrade is something that
worries me a bit, actually, as it could be useful in some cases like
monitoring? That would be fancy, for sure.. For now and seeing a
lack of consensus on this larger matter, I'd like to propose a check
for IsBinaryUpgrade into ApplyLauncherRegister() instead as it makes
no real sense to start apply workers in this context. That would be
equivalent to max_logical_replication_workers = 0.

Amit, Vignesh, would the attached be OK for both of you?

(Vignesh has posted a slightly different version of this patch on a
different thread, but the subscriber part should be part of this
thread with the subscribers, I assume.)
--
Michael