From: Etsuro Fujita <fujita.etsuro@lab.ntt.co.jp>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Ashutosh Bapat <ashutosh.bapat@enterprisedb.com>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: Jeff Janes <jeff.janes@gmail.com>
Cc: David Steele <david@pgmasters.net>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] postgres_fdw bug in 9.6
Date: Thu, 30 Nov 2017 21:55:51 +0900
Message-ID: <5A1FFFD7.6080904@lab.ntt.co.jp> (raw)
In-Reply-To: <27145.1511994722@sss.pgh.pa.us>
References: <CAMkU=1y2G8VOVBHv3iXU2TMAj7-RyBFFW1uhkr5sm9LQ2=X35g@mail.gmail.com>
<22168.1504041271@sss.pgh.pa.us>
<20170905044336.18925.22634.pgcf@coridan.postgresql.org>
<07ed8f27-12cf-8403-d23b-f7d907de4a83@lab.ntt.co.jp>
<CAFjFpRd7fuanj3s-bXpeuLhaRJnFuEWCiwu_-Q4Ox7wGCAW_Mw@mail.gmail.com>
<7031.1507215420@sss.pgh.pa.us>
<25877.1511886076@sss.pgh.pa.us>
<CA+TgmoaUu=QTvfoCVfidXH=CU4_e1nWTMj=jTQpB3eoHYAVpzw@mail.gmail.com>
<CAFjFpRc4f9u60t7VgTiw1quoto5gmXJ0tHMwCfSM5dx253B8fw@mail.gmail.com>
<27145.1511994722@sss.pgh.pa.us>
(2017/11/30 7:32), Tom Lane wrote:
> AFAICT, [1] just demonstrates that nobody had thought about the scenario
> up to that point, not that the subsequently chosen solution was a good
> one. In that example,
>
> LockRows (cost=100.00..101.18 rows=4 width=70)
> Output: tab.a, tab.b, tab.ctid, foo.*, bar.*
> -> Nested Loop (cost=100.00..101.14 rows=4 width=70)
> Output: tab.a, tab.b, tab.ctid, foo.*, bar.*
> Join Filter: (foo.a = tab.a)
> -> Seq Scan on public.tab (cost=0.00..1.01 rows=1 width=14)
> Output: tab.a, tab.b, tab.ctid
> -> Foreign Scan (cost=100.00..100.08 rows=4 width=64)
> Output: foo.*, foo.a, bar.*, bar.a
> Relations: (public.foo) INNER JOIN (public.bar)
> Remote SQL: SELECT l.a1, l.a2, r.a1, r.a2 FROM (SELECT ROW(l.a9), l.a9 FROM (SELECT a a9 FROM public.foo FOR UPDATE) l) l (a1, a2) INNER JOIN (SELECT ROW(r.a9), r.a9 FROM (SELECT a a9 FROM public.bar FOR UPDATE) r) r (a1, a2) ON ((l.a2 = r.a2))
>
> the output of the foreign join cannot change during EPQ, since the remote
> server already locked the rows before returning them. The only thing that
> can change is the output of the local scan on public.tab. Yes, we then
> need to re-verify that foo.a = tab.a ... but in this example, that's the
> responsibility of the NestLoop plan node, not the foreign join.
That's right, but is that true when the FDW uses late row locking?
Best regards,
Etsuro Fujita
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To: pgsql-hackers@postgresql.org
Cc: fujita.etsuro@lab.ntt.co.jp, tgl@sss.pgh.pa.us, ashutosh.bapat@enterprisedb.com, robertmhaas@gmail.com, jeff.janes@gmail.com, david@pgmasters.net
Subject: Re: [HACKERS] postgres_fdw bug in 9.6
In-Reply-To: <5A1FFFD7.6080904@lab.ntt.co.jp>
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