On Thu, 13 Apr 2023 at 13:01, Peter Geoghegan <pg@bowt.ie> wrote:
>
> On Thu, Apr 13, 2023 at 9:45 AM Robert Haas <robertmhaas@gmail.com> wrote:
> >
> > On Wed, Apr 12, 2023 at 4:23 PM Greg Stark <stark@mit.edu> wrote:
> > > Am I crazy or is the parenthetical comment there exactly backwards? If
> > > the horizon is *more recent* then fewer tuples are *non*-removable.
> > > I.e. *more* tuples are removable, no?
> >
> > Isn't it the non-parenthetical part that's wrong? I would expect that
> > if we don't know which relation it is, the horizon might be
> > considerably LESS recent, which would result in fewer tuples being
> > removable.
>
> You can make arguments for either way of restating it being clearer
> than the other.
Yeah, I think Robert is being confused by the implicit double
negative. If we don't know which relation it is it's because relation
is NULL and the comment is talking about if it's "not NULL". I think
you're right that it would be less confusing if it just says "if you
pass NULL we have to give a conservative result which means an older
xid and fewer removable tuples".
But I'm saying the parenthetical part is not just confusing, it's
outright wrong. I guess that just means the first half was so
confusing it confused not only the reader but the author too.
--
greg
