Re: Add recovery to pg_control and remove backup_label

On 11/20/23 19:58, Andres Freund wrote:
> 
> On 2023-11-21 08:52:08 +0900, Michael Paquier wrote:
>> On Mon, Nov 20, 2023 at 12:37:46PM -0800, Andres Freund wrote:
>>> Given that, I wonder if what we should do is to just add a new field to
>>> pg_control that says "error out if backup_label does not exist", that we set
>>> when creating a streaming base backup
>>
>> That would mean that one still needs to take an extra step to update a
>> control file with this byte set, which is something you had a concern
>> with in terms of compatibility when it comes to external backup
>> solutions because more steps are necessary to take a backup, no?
> 
> I was thinking we'd just set it in the pg_basebackup style path, and we'd
> error out if it's set and backup_label is present. But we'd still use
> backup_label without the pg_control flag set.
> 
> So it'd just provide a cross-check that backup_label was not removed for
> pg_basebackup style backup, but wouldn't do anything for external backups. But
> imo the proposal to just us pg_control doesn't actually do anything for
> external backups either - which is why I think my proposal would achieve as
> much, for a much lower price.

I'm not sure why you think the patch under discussion doesn't do 
anything for external backups. It provides the same benefits to both 
pg_basebackup and external backups, i.e. they both receive the updated 
version of pg_control.

I really dislike the idea of pg_basebackup having a special mechanism 
for making recovery safer that is not generally available to external 
backup software. It might be easy enough for some (e.g. pgBackRest) to 
manipulate pg_control but would be out of reach for most.

Regards,
-David