Re: pg_stop_backup(wait_for_archive := true) on standby server

All,

* Masahiko Sawada (sawada(dot)mshk(at)gmail(dot)com) wrote:
> On Tue, Jul 25, 2017 at 4:43 AM, Michael Paquier
> <michael(dot)paquier(at)gmail(dot)com> wrote:
> > On Mon, Jul 24, 2017 at 6:45 PM, Stephen Frost <sfrost(at)snowman(dot)net> wrote:
> >> What the change would do is make the pg_stop_backup() caller block until
> >> the last WAL is archvied, and perhaps that ends up taking hours, and
> >> then the connection is dropped for whatever reason and the backup fails
> >> where it otherwise.... what? wouldn't have been valid anyway at that
> >> point, since it's not valid until the last WAL is actually archived.
> >> Perhaps eventually it would be archived and the caller was planning for
> >> that and everything is fine, but, well, that feels like an awful lot of
> >> wishful thinking.
> >
> > Letting users taking unconsciously inconsistent backups is worse than
> > potentially breaking scripts that were actually not working as
> > Postgres would expect. So I am +1 for back-patching a lighter version
> > of the proposed patch that makes the wait happen on purpose.
> >
> >>> > I'd hate to have to do it, but we could technically add a GUC to address
> >>> > this in the back-branches, no? I'm not sure that's really worthwhile
> >>> > though..
> >>>
> >>> That would be mighty ugly.
> >>
> >> Oh, absolutely agreed.
> >
> > Yes, let's avoid that. We are talking about a switch aimed at making
> > backups potentially inconsistent.
>
> Thank you for the review comments!
> Attached updated the patch. The noting in pg_baseback doc will be
> necessary for back branches if we decided to not back-patch it to back
> branches. So it's not contained in this patch for now.
>
> Regarding back-patching this to back branches, I also vote for
> back-patching to back branches. Or we can fix the docs of back
> branches and fix the code only in PG10. I expect that the user who
> wrote a backup script has done enough functional test and dealt with
> this issue somehow, but since the current doc clearly says that
> pg_stop_backup() waits for all WAL to be archived we have to make a
> consideration about there are users who wrote a wrong backup script.
> So I think we should at least notify it in the minor release.

That sounds like we have at least three folks thinking that this should
be back-patched, and one who doesn't. Does anyone else wish to voice an
opinion regarding back-patching this..?

Thanks!

Stephen