Re: Add recovery to pg_control and remove backup_label

On Mon, Nov 20, 2023 at 12:54 PM David Steele <david@pgmasters.net> wrote:
> Another thing we could do is explicitly error if we see backup_label in
> PGDATA during recovery. That's just a few lines of code so would not be
> a big deal to maintain. This error would only be visible on restore, so
> it presumes that backup software is being tested.

I think that if we do decide to adopt this proposal, that would be a
smart precaution.

> A little hard to add to the tests, I think, since they are purely
> informational, i.e. not pushed up by the parser. Maybe we could just
> grep for the fields?

Hmm. Or should they be pushed up by the parser?

> I think these fields would be handled the same as the rest of the fields
> in backup_label: returned from pg_backup_stop() and also stored in
> backup_manifest. Third-party software can do as they like with them and
> pg_combinebackup can just read from backup_manifest.

I think that would be a bad plan, because this is critical
information, and a backup manifest is not a thing that you're required
to have. It's not a natural fit at all. We don't want to create a
situation where if you nuke the backup_manifest then the server
forgets that what it has is an incremental backup rather than a usable
data directory.

> We absolutely need more people to look at this and sign off. I'm glad
> they have not so far because it has allowed time to whack the patch
> around and get it into better shape.

Cool.

--
Robert Haas
EDB: http://www.enterprisedb.com