Re: postgres_fdw: wrong results with self join + enable_nestloop off

Hi Etsuro Fujita,


Any updates? -- did you get a chance to look into this?


Regards,
Nishant.

On Mon, Apr 17, 2023 at 11:00 AM Nishant Sharma <
nishant.sharma@enterprisedb.com> wrote:

> Thanks Etsuro for your response!
>
> One small typo correction in my answer to "What is the technical issue?"
> "it is *not* considered a pseudo constant" --> "it is considered a pseudo
> constant"
>
>
> Regards,
> Nishant.
>
> On Fri, Apr 14, 2023 at 6:21 PM Etsuro Fujita <etsuro.fujita@gmail.com>
> wrote:
>
>> Hi Nishant,
>>
>> On Fri, Apr 14, 2023 at 8:39 PM Nishant Sharma
>> <nishant.sharma@enterprisedb.com> wrote:
>> > I debugged this issue and was able to find a fix for the same. Kindly
>> please refer to the attached fix. With the fix I am able to resolve the
>> issue.
>>
>> Thanks for the report and patch!
>>
>> > What is the technical issue?
>> > The problem here is the use of extract_actual_clauses. Because of which
>> the plan creation misses adding the second condition of AND i.e "now() <
>> '23-Feb-2020'::timestamp" in the plan. Because it is not considered a
>> pseudo constant and extract_actual_clause is passed with false as the
>> second parameter and it gets skipped from the list. As a result that
>> condition is never taken into consideration as either one-time filter
>> (before or after) or part of SQL remote execution
>> >
>> > Why do I think the fix is correct?
>> > The fix is simple, where we have created a new function similar to
>> extract_actual_clause which just extracts all the conditions from the list
>> with no checks and returns the list to the caller. As a result all
>> conditions would be taken into consideration in the query plan.
>>
>> I think that the root cause for this issue would be in the
>> create_scan_plan handling of pseudoconstant quals when creating a
>> foreign-join (or custom-join) plan.  Anyway, I will look at your patch
>> closely, first.
>>
>> Best regards,
>> Etsuro Fujita
>>
>