Re: Avoiding superfluous buffer locking during nbtree backwards scans

On Fri, 30 Aug 2024 at 21:43, Matthias van de Meent
<boekewurm+postgres(at)gmail(dot)com> wrote:
>
> On Mon, 19 Aug 2024 at 13:43, Matthias van de Meent
> <boekewurm+postgres(at)gmail(dot)com> wrote:
> >
> > On Sun, 11 Aug 2024 at 21:44, Peter Geoghegan <pg(at)bowt(dot)ie> wrote:
> > >
> > > On Tue, Aug 6, 2024 at 6:31 PM Matthias van de Meent
> > > <boekewurm+postgres(at)gmail(dot)com> wrote:
> > > > +1, LGTM.
> > > >
> > > > This changes the backward scan code in _bt_readpage to have an
> > > > approximately equivalent handling as the forward scan case for
> > > > end-of-scan cases, which is an improvement IMO.
> >
> > Here's a new patch that further improves the situation, so that we
> > don't try to re-lock the buffer we just accessed when we're stepping
> > backward in index scans, reducing buffer lock operations in the common
> > case by 1/2.
>
> Attached is an updated version of the patch, now v2, which fixes some
> assertion failures for parallel plans by passing the correct
> parameters to _bt_parallel_release for forward scans.

I noticed I attached an older version of the patch which still had 1
assertion failure case remaining (thanks cfbot), so here's v3 which
solves that problem.

Kind regards,

Matthias van de Meent
Neon (https://neon.tech)