Re: speeding up planning with partitions

Imai-san,

On 2019/03/15 14:40, Imai, Yoshikazu wrote:
> Amit-san,
>
> I have another little comments about v31-patches.
>
> * We don't need is_first_child in inheritance_planner().
>
> On Fri, Mar 8, 2019 at 9:18 AM, Amit Langote wrote:
>> On 2019/03/08 16:16, Imai, Yoshikazu wrote:
>>> I attached the diff of modification for v26-0003 patch which also
>> contains some refactoring.
>>> Please see if it is ok.
>>
>> I like the is_first_child variable which somewhat improves readability,
>> so updated the patch to use it.
>
> I noticed that detecting first child query in inheritance_planner() is already done by "final_rtable == NIL"
>
> /*
> * If this is the first non-excluded child, its post-planning rtable
> * becomes the initial contents of final_rtable; otherwise, append
> * just its modified subquery RTEs to final_rtable.
> */
> if (final_rtable == NIL)
>
> So I think we can use that instead of using is_first_child.

That's a good suggestion. One problem I see with that is that
final_rtable is set only once we've found the first *non-dummy* child.
So, if all the children except the last one are dummy, we'd end up never
reusing the source child objects. Now, if final_rtable was set for the
first child irrespective of whether it turned out to be dummy or not,
which it seems OK to do, then we can implement your suggestion.

Thanks,
Amit