Re: Adding skip scan (including MDAM style range skip scan) to nbtree

Fantastic, the patch is working, it fixes our issue!

Thank you,
Natalya Aksman.

On Wed, Sep 10, 2025 at 3:12 PM Peter Geoghegan <pg(at)bowt(dot)ie> wrote:

> On Wed, Sep 10, 2025 at 2:59 PM Natalya Aksman <natalya(at)tigerdata(dot)com>
> wrote:
> > But after btrescan resets "so->numberOfKeys = 0", so->skipScan is not
> reset to "false" in _bt_preprocess_keys because of this code:
> https://github.com/postgres/postgres/blob/9016fa7e3bcde8ae4c3d63c707143af147486a10/src/backend/access/nbtree/nbtpreprocesskeys.c#L1847
> > After we set "so->numberOfKeys = 0" we quit on line 1847 before we get
> to the line 1874 where we do "so->skipScan = (numSkipArrayKeys > 0);"
> https://github.com/postgres/postgres/blob/9016fa7e3bcde8ae4c3d63c707143af147486a10/src/backend/access/nbtree/nbtpreprocesskeys.c#L1874
>
> It sounds like the patch that I posted fixes the problem, without you
> having to set so->skipScan externally (which sounds like a big
> kludge). Can you confirm that it actually does fix the problem that
> you're seeing?
>
> TimescaleDB isn't following the letter of the law here. But I do still
> see the argument for consistently setting so->skipScan during
> preprocessing. That at least makes sense on general robustness
> grounds.
>
> --
> Peter Geoghegan
>