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From: Andres Freund <andres@anarazel.de>
To: Michael Paquier <michael.paquier@gmail.com>
Cc: ropeladder@gmail.com, PostgreSQL mailing lists <pgsql-bugs@postgresql.org>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Subject: Re: BUG #14843: CREATE TABLE churns through all memory, crashes db
Date: Fri, 6 Oct 2017 11:01:43 -0700
Message-ID: <20171006180143.rq3idmtijbeahjyj@alap3.anarazel.de> (raw)
In-Reply-To: <CAB7nPqRjCoFMFVb7RcG5ztxzmobALij0O21m3-p8qNbxw37ouA@mail.gmail.com>
References: <20171005230321.28561.15927@wrigleys.postgresql.org>
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	<CAB7nPqSV0XkeERHWGfBFQ_-R3eZd1Rmr7BJVdwDkBp=PTzmzGw@mail.gmail.com>
	<CAB7nPqRjCoFMFVb7RcG5ztxzmobALij0O21m3-p8qNbxw37ouA@mail.gmail.com>
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On 2017-10-06 12:57:59 +0900, Michael Paquier wrote:
> On Fri, Oct 6, 2017 at 10:00 AM, Michael Paquier
> <michael.paquier@gmail.com> wrote:
> > This is suspicious:
> >       ExecutorState: 62906368 total in 17 blocks; 13736 free (35
> > chunks); 62892632 used
> 
> The introduction of the ProjectSet node has caused the regressionin
> the executor visibly. A bisect run is showing me this commit as the
> culprit
> commit 69f4b9c85f168ae006929eec44fc44d569e846b9
> Author: Andres Freund <andres@anarazel.de>
> Date:   Wed Jan 18 12:46:50 2017 -0800
> Move targetlist SRF handling from expression evaluation to new executor node.
> 
> I was expecting a leak of some kind first, but valgrind does not
> complain when executing the query eating all the memory. Before this
> commit the memory usage remains low and stable, less than 1% in my
> environments.

It's "just" a MemoryContextSwitchTo() that some idiot^WI forgot and
reviews didn't spot. The ResetExprContext() in ExecProjectSet() is
correctly placed afaict, it's just that we leak (query scope) a lot into
the surrounding memory context.  A MemoryContextSwitchTo() at the top &
bottom of ExecProjectSet() fixes the issue for me.

Greetings,

Andres Freund


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  Subject: Re: BUG #14843: CREATE TABLE churns through all memory, crashes db
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