Re: Updated backup APIs for non-exclusive backups

On 3/22/16 12:31 PM, Magnus Hagander wrote:

> On Tue, Mar 22, 2016 at 5:27 PM, David Steele <david(at)pgmasters(dot)net
> <mailto:david(at)pgmasters(dot)net>> wrote:
>
> > Adding the stop time column should be a simple addition and I don't see
> > a problem with that. I think I misunderstood your original request on
> > that. Because you are just talking about returning a timestamptz with
> > the "right now" value for when you called pg_stop_backup()? Or to be
> > specific, just before pg_Stop_backup *finished*. Or do you mean when
> > pg_stop_backup() started?
>
> What would be ideal is the minimum time that could be used for PITR. In
> an exclusive backup that's the time the end-of-backup record is written
> to WAL. In a non-exlusive backup I'm not quite sure how that works.

I guess I was hoping that you would know. I fine with just getting the
current timestamp as is currently done in do_pg_stop_backup(). It's not
perfect but it will be pretty close.

I thought some more about putting STOP_WAL_LOCATION into the backup
label and I think this is an important step. Without that the recovery
process needs to use pg_control to determine when the database has reach
consistency and that will only work if pg_control was copied last.

In summary, I think the patch should be updated to include stop_time as
a column and add STOP_WAL_LOCATION and STOP_TIME to backup_label. The
recovery process should read STOP_WAL_LOCATION from backup_label and use
that to decide when the database has become consistent.

Thanks,
--
-David
david(at)pgmasters(dot)net