On Sun, Jul 20, 2025 at 1:07 AM Thomas Munro <thomas.munro@gmail.com> wrote:
> On Sat, Jul 19, 2025 at 11:23 PM Tomas Vondra <tomas@vondra.me> wrote:
> > The thing that however concerns me is that what I observed was not the
> > distance getting reset to 1, and then ramping up. Which should happen
> > pretty quickly, thanks to the doubling. In my experiments it *never*
> > ramped up again, it stayed at 1. I still don't quite understand why.
>
> Huh. Will look into that on Monday.
I suspect that it might be working as designed, but suffering from a
bit of a weakness in the distance control algorithm, which I described
in another thread[1]. In short, the simple minded algorithm that
doubles on miss and subtracts one on hit can get stuck alternating
between 1 and 2 if you hit certain patterns. Bilal pinged me off-list
to say that he'd repro'd something like your test case and that's what
seemed to be happening, anyway? I will dig out my experimental
patches that tried different adjustments to escape from that state....
[1] https://www.postgresql.org/message-id/flat/CA%2BhUKGLPakwZiFUa5fQXpYDpCXvZXQ%3DP3cWOGACCoobh7U2r3A%40mail.gmail.com
