| From: | Kouhei Kaigai <kaigai(at)ak(dot)jp(dot)nec(dot)com> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Etsuro Fujita <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>, Shigeru Hanada <shigeru(dot)hanada(at)gmail(dot)com> |
| Subject: | Re: Foreign join pushdown vs EvalPlanQual |
| Date: | 2015-11-20 05:11:28 |
| Message-ID: | 9A28C8860F777E439AA12E8AEA7694F801173DD4@BPXM15GP.gisp.nec.co.jp |
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| Lists: | pgsql-hackers |
> On Thu, Nov 19, 2015 at 6:39 AM, Kouhei Kaigai <kaigai(at)ak(dot)jp(dot)nec(dot)com> wrote:
> > So, are you suggesting to make a patch that allows ForeignScan to have
> > multiple sub-plans right now? Or, one sub-plan?
>
> Two:
>
> http://www.postgresql.org/message-id/CA+TgmoYZeje+ot1kX4wdoB7R7DPS0CWXAzfqZ-
> 14yKfkgKREAQ(at)mail(dot)gmail(dot)com
>
Hmm. Two is a bit mysterious for me because two sub-plans (likely)
means this ForeignScan node checks join clauses and reconstruct
a joined tuple by itself but does not check scan clauses pushed-
down (it is job of inner/outer scan plan, isn't it?).
In this case, how do we treat N-way remote join cases (N>2) if we
assume such a capability in FDW driver?
One subplan means FDW driver run an entire join sub-tree with local
alternative sub-plan; that is my expectation for the majority case.
However, I cannot explain two subplans, but not multiple, well.
Thanks,
--
NEC Business Creation Division / PG-Strom Project
KaiGai Kohei <kaigai(at)ak(dot)jp(dot)nec(dot)com>
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