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>, 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: | 2016-02-05 09:05:47 |
Message-ID: | 56B465EB.7060106@lab.ntt.co.jp |
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On 2016/02/04 21:57, Ashutosh Bapat wrote:
> One more: I think the following in postgresGetForeignJoinPaths() is
> a good idea, but I think it's okay to just check whether
> root->rowMarks is non-NIL, because that since we have rowmarks for
> all base relations except the target, if we have
> root->parse->commandType==CMD_DELETE (or
> root->parse->commandType==CMD_UPDATE), then there would be at least
> one non-target base relation in the joinrel, which would have a rowmark.
> Sorry, I am unable to understand it fully. But what you are suggesting
> that if there are root->rowMarks, then we are sure that there is at
> least one base relation apart from the target, which needs locking rows.
> Even if we don't have one, still changes in a row of target relation
> after it was scanned, can result in firing EPQ check, which would need
> the local plan to be executed, thus even if root->rowMarks is NIL, EPQ
> check can fire and we will need alternate local plan.
Yeah, I think that is true, but if root->rowMarks==NIL, we won't have
non-target foreign tables, and therefore postgresGetForeignJoinPaths()
will never be called. No?
Best regards,
Etsuro Fujita
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