Re: old_snapshot_threshold bottleneck on replica

On Wed, Jun 14, 2023 at 3:56 PM Thomas Munro <thomas(dot)munro(at)gmail(dot)com> wrote:
> On Tue, Feb 14, 2023 at 9:45 AM Andres Freund <andres(at)anarazel(dot)de> wrote:
> > Indeed. There's a lot of things wrong with it. We have reproducers for
> > creating wrong query results. Nobody has shown interest in fixing the
> > problems, for several years by now. It costs users that *do not* use the
> > feature performance (*).
> >
> > I think we're doing our users a disservice by claiming to have this feature.
> >
> > I don't think a lot of the existing code would survive if we were to create a
> > newer version, more maintainable / reliable, version of the feature.
>
> I raised this at the recent developer meeting and the assembled
> hackers agreed. Does anyone think we *shouldn't* drop the feature? I
> volunteered to write a removal patch for v17, so here's a first run
> through to find all the traces of this feature. In this first go I
> removed everything I could think of, but we might want to keep some
> vestiges. I guess we might want to keep the registered error
> class/code? Should we invent a place where we keep stuff like #define
> TestForOldSnapshot(...) expanding to nothing for some amount of time,
> for extensions? I dunno, I bet extensions doing stuff that
> sophisticated already have a bunch of version tests anyway. I suppose
> keeping the GUC wouldn't really be helpful (if you're using it, you
> probably want to know that it isn't available anymore and think about
> the implications for your application).

Done.

I hope we get "snapshot too old" back one day.