From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
cc: Andres Freund <andres@anarazel.de>,
        Pavel Stehule <pavel.stehule@gmail.com>,
        "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Subject: Re: slow queries over information schema.tables
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Comments: In-reply-to Robert Haas <robertmhaas@gmail.com>
	message dated "Thu, 06 Dec 2018 11:50:48 -0500"
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Date: Thu, 06 Dec 2018 12:03:33 -0500
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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