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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Andres Freund <andres@anarazel.de>
Cc: Pavel Stehule <pavel.stehule@gmail.com>
Cc: pgsql-hackers@postgresql.org <pgsql-hackers@postgresql.org>
Subject: Re: slow queries over information schema.tables
Date: Thu, 06 Dec 2018 12:03:33 -0500
Message-ID: <21728.1544115813@sss.pgh.pa.us> (raw)
In-Reply-To: <CA+TgmoaNhWkCt2MBpvhHX2ckJd=JHTqDAS1oXRdQPuVtp2MD=g@mail.gmail.com>
References: <CAFj8pRBUCX4LZ2rA2BbEkdD6NN59mgx+BLo1gO08Wod4RLtcTg@mail.gmail.com>
	<5978.1544030694@sss.pgh.pa.us>
	<20181205175657.s7mt6as356kwvrji@alap3.anarazel.de>
	<8210.1544034143@sss.pgh.pa.us>
	<20181205182555.x4wtnzffmhwsc3c7@alap3.anarazel.de>
	<8843.1544035292@sss.pgh.pa.us>
	<CA+TgmobB=Ky_GOa4-M3afJHup3LC9FoV-tLmU--XBdV+8Do-Tg@mail.gmail.com>
	<20577.1544113962@sss.pgh.pa.us>
	<CA+TgmoaNhWkCt2MBpvhHX2ckJd=JHTqDAS1oXRdQPuVtp2MD=g@mail.gmail.com>

Robert Haas <robertmhaas@gmail.com> writes:
> On Thu, Dec 6, 2018 at 11:32 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> It's fairly hard to imagine practical cases where we'd not call
>> AcceptInvalidationMessages at least once per query, so I'm not
>> very sure what you're on about.

> Unless I'm confused, it happens any time you run a query that only
> touches tables using lockmodes previously acquired by the current
> transaction.  Like:

> BEGIN;
> some query;
> the same query again;

In my testing, that still hits AIM() during parserOpenTable().

[ further experimentation... ]  It looks like if you prepare
a query and then just execute it repeatedly in one transaction,
you'd not reach AIM (as long as you were getting generic plans).
Possibly that's a gap worth closing.

			regards, tom lane




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