Re: Save a few bytes in pg_attribute

On Tue, 21 Mar 2023 at 20:58, Andres Freund <andres(at)anarazel(dot)de> wrote:
>
> Hi,
>
> On 2023-03-21 20:20:40 +0100, Matthias van de Meent wrote:
> > On Tue, 21 Mar 2023 at 19:55, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> > >
> > > Andres Freund <andres(at)anarazel(dot)de> writes:
> > > > FWIW, I think we should consider getting rid of attcacheoff. I doubt it's
> > > > worth its weight these days, because deforming via slots starts at the
> > > > beginning anyway. The overhead of maintaining it is not insubstantial, and
> > > > it's just architecturally ugly to to update tupledescs continually.
> > >
> > > I'd be for that if we can convince ourselves there's not a material
> > > speed penalty. As you say, it's quite ugly.
> >
> > Yes, attcacheoff is a tremendous performance boon in many cases.
>
> Which? We don't use fastgetattr() in many places these days. And in some quick
> measurements it's a wash or small loss when deforming slot tuples, even when
> the attcacheoff optimization would apply, because the branches for managing it
> add more overhead than they safe.

My experience with attcacheoff performance is in indexes, specifically
index_getattr(). Sure, multi-column indexes are uncommon, but the
difference between have and have-not for cached attribute offsets is
several %.

Kind regards,

Matthias van de Meent