Re: Reviewing freeze map code

On 2016-06-06 05:34:32 -0400, Robert Haas wrote:
> On Mon, Jun 6, 2016 at 5:11 AM, Michael Paquier
> <michael(dot)paquier(at)gmail(dot)com> wrote:
> >> Attached is a sample patch that controls full page vacuum by new GUC parameter.
> >
> > Don't we want a reloption for that? Just wondering...
>
> Why? Just for consistency? I think the bigger question here is
> whether we need to do anything at all. It's true that, without some
> new option, we'll lose the ability to forcibly vacuum every page in
> the relation, even if all-frozen. But there's not much use case for
> that in the first place. It will be potentially helpful if it turns
> out that we have a bug that sets the all-frozen bit on pages that are
> not, in fact, all-frozen. Otherwise, what's the use?

Except that we right now don't have any realistic way to figure out
whether this new feature actually does the right thing. Which makes
testing this *considerably* harder than just VACUUM (dwim). I think it's
unacceptable to release this feature without a way that'll tell that it
so far has/has not corrupted the database. Would that, in a perfect
world, be vacuum? No, probably not. But since we're not in a perfect world...

Andres