Re: Push down more full joins in postgres_fdw

On Thu, Jan 5, 2017 at 5:51 PM, Etsuro Fujita
<fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp> wrote:
> On 2017/01/05 21:11, Ashutosh Bapat wrote:
>>
>> On Thu, Jan 5, 2017 at 5:14 PM, Etsuro Fujita
>> <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp> wrote:
>>>
>>> On 2017/01/03 17:28, Ashutosh Bapat wrote:
>>>>
>>>> In build_subquery_tlists(), why don't we handle base relations?
>>>> + if (foreignrel->reloptkind != RELOPT_JOINREL)
>>>> + return;
>
>
>>> The reason for that is we don't need to handle the baserel cases; the
>>> tlist
>>> for a base relation, if needed, would be created while recursing into a
>>> join
>>> relation that joins the base relation to other base/join relation.
>
>
>> Right. Sorry, I misunderstood the code. May be a comment would help.
>
>
> Will add the comment.
>
>>>> Also, in this function, if fpinfo->tlist is already set, why do we want
>>>> to
>>>> build it again?
>
>
>>> When this function gets called, fpinfo->tlist isn't set for any base or
>>> join
>>> relation that needs to build the tlist, so we always need to build it for
>>> each such relation.
>
>
>> IIUC, for a relation with use_remote_estimates we will deparse the
>> query twice and will build the targetlist twice.
>
>
> That's right. We could avoid the duplicate work the way you proposed, but I
> was thinking to leave that for another patch. Should we do that in this
> patch?

If you are agree that the change is needed, it's better to do it in
this patch itself if we can, instead of a one liner patch.
>
>>>> In build_tlist_to_deparse(), if fpinfo->tlist for the given relation is
>>>> set, we
>>>> should just return it rather than constructing it again.
>
>
>>> In that function we wouldn't have such cases for base or join relations
>>> needing the tlist.
>
>
>> Same explanation as above.
>
>
> Will revise if it's better to do that in this patch.

Thanks.

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