Message-ID: <5f727153d2593bcd0454d4897eb387da60c90c94.camel@cybertec.at>
Subject: Re: Using a lot of memory in each session.
From: Laurenz Albe <laurenz.albe@cybertec.at>
To: DBA <ecountdba@ecounterp.co.kr>, "pgsql-bugs@lists.postgresql.org"
	 <pgsql-bugs@lists.postgresql.org>
Date: Tue, 24 Sep 2024 17:45:14 +0200
In-Reply-To: <20240924075811.BDA2C10AA13@wsmtpa1.ecounterp.com>
References: <20240924075811.BDA2C10AA13@wsmtpa1.ecounterp.com>
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On Tue, 2024-09-24 at 16:58 +0900, DBA wrote:
> We set shared_buffer =3D 70GB, max_connections =3D 300, work_mem =3D 300M=
B.
>=20
> We thought the session memory could be adjusted with the work_mem variabl=
e, but no.
> noticed that each session consumed more than 500MB.

work_mem limits the memory used by a single execution plan step, so a singl=
e
backend can use way more memory.
Moreover, there is hash_mem_multiplier, which defaults to 2 in v15, so a
hash may use twice as much memory.

You didn't tell us how much RAM you have, but your setting of shared_buffer=
s
is probably too high, and you most likely should also reduce work_mem,
particularly if you allow hundreds of connections.

Anyway, I see no bug here.

Yours,
Laurenz Albe