From: | Etsuro Fujita <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp> |
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To: | Ashutosh Bapat <ashutosh(dot)bapat(at)enterprisedb(dot)com> |
Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Push down more full joins in postgres_fdw |
Date: | 2017-01-05 12:21:56 |
Message-ID: | 1380ca32-68c8-5523-58c6-ff8c3bd58496@lab.ntt.co.jp |
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Lists: | pgsql-hackers |
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?
>>> 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.
Best regards,
Etsuro Fujita
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