Re: Trying to understand a failed upgrade in AWS RDS

On Sun, 2023-05-21 at 07:56 -0700, Mike Lissner wrote:
> > As far as I know it's impossible to reliably pg_upgrade a node
> > that has subscriptions and eventually resume logical
> > replication. 
> >
>
>
> Should this go in the documentation somewhere? Maybe in the
> pg_upgrade notes? I still don't understand the mechanism. You also
> say that:
>  
> > It's possible to make it work with some efforts in some basic
> > configurations and / or if no changes happen on the publications
> >
>
>
> But that kind of surprises me too, actually, because it seemed like
> pg_upgrade wiped out the LSN locations of the subcriber, making it
> start all over.
>
> Upgrading a subscriber seems like something that could/should work,
> so it should be documented if pg_upgrade is incompatible with
> maintaining a subscription, shouldn't it?

The docs are strangely silent on this. AFAIK pg_upgrade on either the
publisher or subscriber breaks logical replication, which does make
sense since pg_upgrade basically makes a new database cluster as it
runs.

There is a way to manually set the LSN position of an enabled=false
replication slot, but I've failed to make that work right in tests so
far.