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@pgmasters.net
<mailto:david@pgmasters.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.