Re: Add exclusive backup deprecation notes to documentation

Greetings,

* Peter Eisentraut (peter(dot)eisentraut(at)2ndquadrant(dot)com) wrote:
> On 2019-03-07 10:33, David Steele wrote:
> > On 3/1/19 3:14 PM, Laurenz Albe wrote:
> >> Magnus Hagander wrote:
> >>> Maybe have the first note say "This method is deprecated bceause it has serious
> >>> risks (see bellow)" and then list the actual risks at the end?
> >>
> >> Good idea. That may attract the attention of the dogs among the readers.
> >
> > OK, here's a new version that splits the deprecation notes from the
> > discussion of risks. I also fixed the indentation.
>
> The documentation changes appear to continue the theme from the other
> thread that the exclusive backup mode is terrible and everyone should
> feel bad about it. I don't think there is consensus about that.

I don't view it as up for much debate. The exclusive backup mode is
quite bad.

> I do welcome a more precise description of the handling of backup_label
> and a better hint in the error message. I think we haven't gotten to
> the final shape there yet, especially for the latter. I suggest to
> focus on that.

There isn't a way to handle the backup_label in a sane way when it's
created by the server in the data directory, which is why the
non-exclusive mode explicitly doesn't do that.

> I think it would be helpful to frame the documentation in a way to
> suggest that the nonexclusive mode is more for automation and more
> sophisticated tools and the exclusive mode is more for manual or simple
> scripted use.

I don't agree with this at all, that's not the reason the two exist nor
were they ever developed with the intent that one is for the 'simple'
case and one is for the 'automated' case. Trying to wedge them into
that framework strikes me as simply trying to sweep the serious issues
under the rug and I don't agree with that- if we are going to continue
to have this, we need to make it clear what the issues are. Sadly, we
will still have users who don't actually read the docs that carefully
and get bit by the exclusive backup mode because they didn't appreciate
the issues, but we will continue to have that until we finally remove
the exclusive mode.

> If we do think that the exclusive mode will be removed in PG13, then I
> don't think we need further documentation changes. It already says it's
> deprecated, and we don't need to justify that at length. But again, I'm
> not convinced that that will happen.

There were at least a few comments made on this thread that it wasn't
made clear enough in the documentation that it's deprecated. Saying
that we already deprecated it doesn't change that and doesn't do
anything to actually address those concerns. Continuing to carry
forward these two modes makes further progress in this area difficult
and unlikely to happen, and that's disappointing.

Thanks!

Stephen