Re: About displaying NestLoopParam

On Fri, Sep 16, 2022 at 5:59 PM Richard Guo <guofenglinux@gmail.com> wrote:

> I'm not saying this is a bug, but just curious why param 0 cannot be
> displayed as the referenced expression. And I find the reason is that in
> function find_param_referent(), we have the 'in_same_plan_level' flag
> controlling that if we have emerged from a subplan, i.e. not the same
> plan level any more, we would not look further for the matching
> NestLoopParam. Param 0 suits this situation.
>
> And there is a comment there also saying,
>
>     /*
>      * NestLoops transmit params to their inner child only; also, once
>      * we've crawled up out of a subplan, this couldn't possibly be
>      * the right match.
>      */
>

After thinking of this for more time, I still don't see the reason why
we cannot display NestLoopParam after we've emerged from a subplan.

It seems these params are from parameterized subqueryscan and their
values are supplied by an upper nestloop. These params should have been
processed in process_subquery_nestloop_params() that we just add the
PlannerParamItem entries to root->curOuterParams, in the form of
NestLoopParam, using the same PARAM_EXEC slots.

So I propose the patch attached to remove the 'in_same_plan_level' flag
so that we can display NestLoopParam across subplan. Please correct me
if I'm wrong.

Thanks
Richard