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From: Jehan-Guillaume de Rorthais <jgdr@dalibo.com>
To: Justin Pryzby <pryzby@telsasoft.com>
Cc: pgsql-hackers@lists.postgresql.org
Subject: Re: Memory leak from ExecutorState context?
Date: Wed, 1 Mar 2023 10:46:12 +0100
Message-ID: <20230301104612.7799b105@karst> (raw)
In-Reply-To: <20230228182508.GA30529@telsasoft.com>
References: <20230228190643.1e368315@karst>
	<20230228182508.GA30529@telsasoft.com>

Hi Justin,

On Tue, 28 Feb 2023 12:25:08 -0600
Justin Pryzby <pryzby@telsasoft.com> wrote:

> On Tue, Feb 28, 2023 at 07:06:43PM +0100, Jehan-Guillaume de Rorthais wrote:
> > Hello all,
> > 
> > A customer is facing out of memory query which looks similar to this
> > situation:
> > 
> >   https://www.postgresql.org/message-id/flat/12064.1555298699%40sss.pgh.pa.us#eb519865575bbc549007878a...
> > 
> > This PostgreSQL version is 11.18. Some settings:  
> 
> hash joins could exceed work_mem until v13:

Yes, I am aware of this. But as far as I understand Tom Lane explanations from
the discussion mentioned up thread, it should not be ExecutorState.
ExecutorState (13GB) is at least ten times bigger than any other context,
including HashBatchContext (1.4GB) or HashTableContext (16MB). So maybe some
aggregate is walking toward the wall because of bad estimation, but something
else is racing way faster to the wall. And presently it might be something
related to some JOIN node.

About your other points, you are right, there's numerous things we could do to
improve this query, and our customer is considering it as well. It's just a
matter of time now.

But in the meantime, we are facing a query with a memory behavior that seemed
suspect. Following the 4 years old thread I mentioned, my goal is to inspect
and provide all possible information to make sure it's a "normal" behavior or
something that might/should be fixed.

Thank you for your help!

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