| From: | Etsuro Fujita <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp> |
|---|---|
| To: | Ashutosh Bapat <ashutosh(dot)bapat(at)enterprisedb(dot)com> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Jeevan Chalke <jeevan(dot)chalke(at)enterprisedb(dot)com>, Thom Brown <thom(at)linux(dot)com>, "pgsql-hackers(at)postgreSQL(dot)org" <pgsql-hackers(at)postgresql(dot)org>, Kouhei Kaigai <kaigai(at)ak(dot)jp(dot)nec(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Shigeru Hanada <shigeru(dot)hanada(at)gmail(dot)com> |
| Subject: | Re: postgres_fdw join pushdown (was Re: Custom/Foreign-Join-APIs) |
| Date: | 2016-02-16 06:56:41 |
| Message-ID: | 56C2C829.3060403@lab.ntt.co.jp |
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| Lists: | pgsql-hackers |
On 2016/02/16 15:22, Ashutosh Bapat wrote:
> During join planning, the planner tries multiple combinations of joining
> relations, thus the same base or join relation can be part of multiple
> of combination. Hence remote_conds or joinclauses will get linked
> multiple times as they are bidirectional lists, thus breaking linkages
> of previous join combinations tried. E.g. while planning A join B join C
> join D planner will come up with combinations like A(B(CD)) or (AB)(CD)
> or ((AB)C)D etc. and remote_conds from A will first be linked into
> A(B(CD)), then AB breaking the first linkages.
Exactly, but I don't think that that needs to be considered because we
have this at the beginning of postgresGetGForeignJoinPaths:
/*
* Skip if this join combination has been considered already.
*/
if (joinrel->fdw_private)
return;
Best regards,
Etsuro Fujita
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