From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
---|---|
To: | Kouhei Kaigai <kaigai(at)ak(dot)jp(dot)nec(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: | 2015-11-19 03:35:59 |
Message-ID: | CA+TgmoYm7tigGxLCLM1rSr96uCACPXodB_O7zp30gE9=FsLXPQ@mail.gmail.com |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-hackers |
On Tue, Nov 17, 2015 at 10:22 PM, Kouhei Kaigai <kaigai(at)ak(dot)jp(dot)nec(dot)com> wrote:
> Apart from EPQ rechecks, the above aggressive push-down idea allows to send
> contents of multiple relations to the remote side. In this case, ForeignScan
> needs to have multiple sub-plans.
>
> For example, please assume here is three relations; tbl_A and tbl_B are
> local and small, tbl_F is remote and large.
> In case when both of (tbl_A JOIN tbl_F) and (tbl_B JOIN tbl_F) produces
> large number of rows thus consumes deserved amount of network traffic but
> (tbl_A JOIN tbl_B JOIN tbl_F) produce small number of rows, the optimal
> strategy is to send local contents to the remote side once then run
> a remote query here to produce relatively smaller rows.
> In the implementation level, ForeignScan shall represent (tbl_A JOIN tbl_B
> JOIN tbl_F), then it returns a bunch of joined tuples. Its remote query
> contains VALUES(...) clauses to pack contents of the tbl_A and tbl_B, thus,
> it needs to be capable to execute underlying multiple scan plans and fetch
> tuples prior to remote query execution.
Hmm, maybe. I'm not entirely sure multiple subplans is the best way
to implement that, but let's argue about that another day.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
From | Date | Subject | |
---|---|---|---|
Next Message | Marko Tiikkaja | 2015-11-19 03:40:00 | proposal: LISTEN * |
Previous Message | Robert Haas | 2015-11-19 03:34:23 | Re: Foreign join pushdown vs EvalPlanQual |