Re: Problem, partition pruning for prepared statement with IS NULL clause.

The comment /* not needed for Consts */ may be more better close to if
(!IsA(expr, Const)).
Others look good to me.

David Rowley <dgrowleyml(at)gmail(dot)com> 于2023年10月9日周一 07:28写道：

> On Sat, 7 Oct 2023 at 03:11, Sergei Glukhov <s(dot)glukhov(at)postgrespro(dot)ru>
> wrote:
> > I noticed that combination of prepared statement with generic plan and
> > 'IS NULL' clause could lead partition pruning to crash.
>
> > Test case:
> > ------
> > set plan_cache_mode to force_generic_plan;
> > prepare stmt AS select * from hp where a is null and b = $1;
> > explain execute stmt('xxx');
>
> Thanks for the detailed report and proposed patch.
>
> I think your proposed fix isn't quite correct. I think the problem
> lies in InitPartitionPruneContext() where we assume that the list
> positions of step->exprs are in sync with the keyno. If you look at
> perform_pruning_base_step() the code there makes a special effort to
> skip over any keyno when a bit is set in opstep->nullkeys.
>
> It seems that your patch is adjusting the keyno that's given to the
> PruneCxtStateIdx() and it looks like (for your test case) it'll end up
> passing keyno==0 when it should be passing keyno==1. keyno is the
> index of the partition key, so you can't pass 0 when it's for key
> index 1.
>
> I wonder if it's worth expanding the tests further to cover more of
> the pruning cases to cover run-time pruning too.
>

I think it's worth doing that.

David
>