Re: Remove Deprecated Exclusive Backup Mode

On Tue, Feb 26, 2019 at 6:31 PM Christophe Pettus <xof(at)thebuild(dot)com> wrote:

>
>
> > On Feb 26, 2019, at 09:26, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> >
> > On Tue, Feb 26, 2019 at 12:20 PM Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
> wrote:
> >> So, let me clarify the situations;
> >>
> >> (1) If backup_label and recovery.signal exist, the recovery starts
> safely.
> >> This is the normal case of recovery from the base backup.
> >>
> >> (2)If backup_label.pending and recovery.signal exist, as described
> above,
> >> PANIC error happens at the start of recovery. This case can happen
> >> if the operator forgets to rename backup_label.pending, i.e.,
> >> operation mistake. So, after PANIC, the operator needs to fix her
> or
> >> his mistake (i.e., rename backup_label.pending) and restart
> >> the recovery.
> >>
> >> (3) If backup_label.pending exists but recovery.signal doesn't, the
> server
> >> ignores (or removes) backup_label.pending and do the recovery
> >> starting the pg_control's REDO location. This case can happen if
> >> the server crashes while an exclusive backup is in progress.
> >> So crash-in-the-middle-of-backup doesn't prevent the recovery from
> >> starting in this idea.
> >
> > The if-conditions for 1 and 2 appear to be the same, which is confusing.
>
> I believe #1 is when backup_label (no .pending) exists, #2 is when
> backup_label.pending (with .pending) exists.
>
> At the absolute minimum, this discussion has convinced me that we need to
> create a wiki page to accurately describe the failure scenarios for both
> exclusive and non-exclusive backups, and the recovery actions for them. If
> it exists already, my search attempts weren't successful. If it doesn't,
> I'm happy to start one.
>

That should not be a wiki page, really, that should be part of the main
documentation.

It can be drafted on the wiki of course, but we *really* should get
something like that into the docs. Because that's what people are going to
read. They'd only go look for the information on the wiki if they knew
there was a problem and needed the details, and the big issue is that
people don't know there are issues in the first place.

--
Magnus Hagander
Me: https://www.hagander.net/ <http://www.hagander.net/>
Work: https://www.redpill-linpro.com/ <http://www.redpill-linpro.com/>