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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Joe Conway <mail@joeconway.com>
Cc: Ashutosh Bapat <ashutosh.bapat@enterprisedb.com>
Cc: Etsuro Fujita <fujita.etsuro@lab.ntt.co.jp>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: Pg Hackers <pgsql-hackers@postgresql.org>
Cc: Rushabh Lathia <rushabh.lathia@gmail.com>
Cc: Michael Paquier <michael.paquier@gmail.com>
Subject: Re: postgres_fdw: perform UPDATE/DELETE .. RETURNING on a join directly
Date: Mon, 05 Mar 2018 17:07:10 -0500
Message-ID: <22164.1520287630@sss.pgh.pa.us> (raw)
In-Reply-To: <857d2c90-492a-028e-37b9-66d86d8cd5dc@joeconway.com>
References: <5A438A45.2000909@lab.ntt.co.jp>
	<5A7BE8E6.200@lab.ntt.co.jp>
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	<CA+Tgmobf+AXEwO4r0oCkvNhkaVnxPgoJaApoX+rAi0G7-N-Dyg@mail.gmail.com>
	<5A7CFDDA.8050906@lab.ntt.co.jp>
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	<20134.1518201188@sss.pgh.pa.us>
	<CA+TgmoY5KNf-Y=zOdHVfa8Lmo=OMJe=dBpP-noT_1fdVK6EYPA@mail.gmail.com>
	<18653.1518297871@sss.pgh.pa.us>
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	<23783.1519929258@sss.pgh.pa.us>
	<5A9928F1.2010206@lab.ntt.co.jp>
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	<CAFjFpRdQVqCrYXN3F=jj_wftSp2gD-rPXKS-ogoQLAmrmKxwuQ@mail.gmail.com>
	<21358.1520229112@sss.pgh.pa.us>
	<25502.1520277552@sss.pgh.pa.us>
	<857d2c90-492a-028e-37b9-66d86d8! cd5dc@joeconway.com>

Joe Conway <mail@joeconway.com> writes:
> On 03/05/2018 11:19 AM, Tom Lane wrote:
>> Joe, I wonder if you could add "log_autovacuum_min_duration = 0" to
>> rhinoceros' extra_config options, temporarily?  Correlating that log
>> output with the log_statement output from the test proper would let
>> us confirm or deny whether it's autovacuum.

> Done just now. Do you want me to force a run?

Both of these runs

https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=rhinoceros&dt=2018-03-05%2020%3A35%3A00
https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=rhinoceros&dt=2018-03-05%2021%3A45%3A02

appear to exonerate autovacuum, and the second seems to destroy the
behind-the-scenes-ANALYZE theory entirely, since there was no change
in the outputs of the extra instrumentation queries.  (In theory
there's a window for ANALYZE to have occurred in between, but that's
not very credible.)

So you can revert the rhinoceros config change if you like --- thanks
for making it so quickly!

Meanwhile, I'm back to wondering what could possibly have affected
the planner's estimates, if pg_proc and pg_statistic didn't change.
I confess bafflement ... but we've now eliminated the autovacuum-
did-it theory entirely, so it's time to start looking someplace else.
I wonder if something in the postgres_fdw remote join machinery
is not as deterministic as it should be.

			regards, tom lane




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