Re: inherit support for foreign tables

On Tue, Jul 1, 2014 at 12:25 PM, Etsuro Fujita <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp>
wrote:

> (2014/07/01 15:13), Ashutosh Bapat wrote:
>
>> On Tue, Jul 1, 2014 at 7:39 AM, Etsuro Fujita
>> <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp <mailto:fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp>> wrote:
>>
>
> We may want to modify use_physical_tlist(), to return false, in case of
>> foreign tables. BTW, it does return false for inheritance trees.
>>
>
> Yeah, but please consider cases where foreign tables are not inheritance
> child rels (and any system columns are requested).
>
>
> 486 /*
>> 487 * Can't do it with inheritance cases either (mainly because
>> Append
>> 488 * doesn't project).
>> 489 */
>> 490 if (rel->reloptkind != RELOPT_BASEREL)
>> 491 return false;
>>
>> Yeah, we can call build_physical_tlist() (and do that in some
>> cases), but if we call the function, it would generate a tlist that
>> contains all Vars in the relation, not only those Vars actually
>> needed by the query (ie, Vars in reltargetlist), and thus it would
>> take more cycles to compute attr_used from the tlist than from
>> reltargetlist. That' what I wanted to say.
>>
>
> Maybe I'm missing something, but what's the point of using the tlist, not
> reltargetlist?
>
>
Compliance with other create_*scan_plan() functions. The tlist passed to
those functions is sometimes preprocessed in create_scan_plan() and some of
the function it calls. If we use reltargetlist directly, we loose that
preprocessing. I have not see any of create_*scan_plan() fetch the
targetlist directly from RelOptInfo. It is always the one supplied by
build_path_tlist() or disuse_physical_tlist() (which in turn calls
build_path_tlist()) or build_physical_tlist().

>
> Thanks,
>
> Best regards,
> Etsuro Fujita
>

--
Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company