Re: Updated backup APIs for non-exclusive backups

On Tue, Mar 29, 2016 at 11:39 PM, Magnus Hagander <magnus@hagander.net> wrote:

On Tue, Mar 29, 2016 at 6:40 PM, Magnus Hagander <magnus@hagander.net> wrote:

So - I can definitely see the argument for returning the stop wal *location*. But I'm still not sure what the definition of the time would be? We can't return it before we know what it means...

I had a chat with Heikki, and here's another suggestion:

1. We don't touch the current exclusive backups at all, as previously discussed, other than deprecating their use. For backwards compat.

2. For new backups, we return the contents of pg_control as a bytea from pg_stop_backup(). We tell backup programs they are supposed to write this out as pg_control.backup, *not* as pg_control.

3a. On recovery, if it's an exlcusive backup, we do as we did before.

3b. on recovery, in non-exclusive backups (determined from backup_label), we check that pg_control.backup exists *and* that pg_control does *not* exist.

Currently pg_control has been read before backup_label file, so as per this proposal do you want to change that?  If yes, I think that will make this patch more invasive with respect to handling of failure modes.  Also as David points out, I also feel that it will raise the bar for usage of this API.