Re: About displaying NestLoopParam
| От | Richard Guo |
|---|---|
| Тема | Re: About displaying NestLoopParam |
| Дата | |
| Msg-id | CAMbWs48S_L0As8iDVM=u55_4_fv=0wHJOA1g65SUEPo1zSZ=7w@mail.gmail.com обсуждение исходный текст |
| Ответ на | About displaying NestLoopParam (Richard Guo <guofenglinux@gmail.com>) |
| Ответы |
Re: About displaying NestLoopParam
|
| Список | pgsql-hackers |
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
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
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