Re: Add recovery to pg_control and remove backup_label

On 1/29/24 12:28, David Steele wrote:
> On 1/28/24 19:11, Michael Paquier wrote:
>> On Fri, Jan 26, 2024 at 06:27:30PM +0530, vignesh C wrote:
>>> Please post an updated version for the same.
>>>
>>> [1] - http://cfbot.cputube.org/patch_46_3511.log
>>
>> With the recent introduction of incremental backups that depend on
>> backup_label and the rather negative feedback received, I think that
>> it would be better to return this entry as RwF for now.  What do you
>> think?
> 
> I've been thinking it makes little sense to update the patch. It would 
> be a lot of work with all the new changes for incremental backup and 
> since Andres and Robert appear to be very against the idea, I doubt it 
> would be worth the effort.

I've had a new idea which may revive this patch. The basic idea is to 
keep backup_label but also return a copy of pg_control from 
pg_stop_backup(). This copy of pg_control would be safe from tears and 
have a backupLabelRequired field set (as Andres suggested) so recovery 
cannot proceed without the backup label.

So, everything will continue to work as it does now. But, backup 
software can be enhanced to write the improved pg_control that is 
guaranteed not to be torn and has protection against a missing backup label.

Of course, pg_basebackup will write the new backupLabelRequired field 
into pg_control, but this way third party software can also gain 
advantages from the new field.

Thoughts?

Regards,
-David