Re: pg_upgrade libraries check

On 05/27/2012 11:31 AM, Tom Lane wrote:
>
>
> Having said that, I've got to also say that I think we've fundamentally
> blown it with the current approach to upgrading extensions. Because we
> dump all the extension member objects, the extension contents have got
> to be restorable into a new database version as-is, and that throws away
> most of the flexibility that we were trying to buy with the extension
> mechanism. IMO we have *got* to get to a place where both pg_dump and
> pg_upgrade dump extensions just as "CREATE EXTENSION", and the sooner
> the better. Once we have that, this type of issue could be addressed by
> having different contents of the extension creation script for different
> major server versions --- or maybe even the same server version but
> different python library versions, to take something on-point for this
> discussion. For instance, Andrew's problem could be dealt with if the
> backport were distributed as an extension "json-backport", and then all
> that's needed in a new installation is an empty extension script of that
> name.

It sounds nice, but we'd have to make pg_upgrade drop its current
assumption that libraries wanted in the old version will be named the
same (one for one) as the libraries wanted in the new version. Currently
it looks for every shared library named in probin (other than
plpgsql.so) in the old cluster and tries to LOAD it in the new cluster,
and errors out if it can't.

My current unspeakably ugly workaround for this behaviour is to supply a
dummy library for the new cluster. The only other suggestion I have
heard (from Bruce) to handle this is to null out the relevant probin
entries before doing the upgrade. I'm not sure if that's better or
worse. It is certainly just about as ugly.

So pg_upgrade definitely needs to get a lot smarter IMNSHO.

cheers

andrew