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From: Marc Millas <[email protected]>
To: Laurenz Albe <[email protected]>
Cc: [email protected] <[email protected]>
Subject: Re: postgres in swap space
Date: Tue, 18 Nov 2025 21:23:18 +0100
Message-ID: <CADX_1aah__ktrnw-yT5ADp6ppxVpz=r6_ZHLQ0cmM=ZgfOMzZg@mail.gmail.com> (raw)
In-Reply-To: <[email protected]>
References: <CADX_1ab6U-T_SZP7L1uiOMNdBm9vV07u22i-KgQvu1E=BHguWA@mail.gmail.com>
	<[email protected]>

Clear !
thanks Laurentz

Marc MILLAS
Senior Architect
+33607850334
www.mokadb.com



On Mon, Nov 17, 2025 at 9:50 PM Laurenz Albe <[email protected]>
wrote:

> On Mon, 2025-11-17 at 18:25 +0100, Marc Millas wrote:
> > Can someone point me to any doc describing why and how much space
> postgres uses on the swap of a debian machine ?
> > it's an old postgres 10, because it is used by a product for which only
> this version is certified.
> > (no comment on that, please)
>
> I'm biting down a comment.
>
> PostgreSQL itself doesn't use any swap space.
>
> The kernel can decide to swap out memory used by PostgreSQL.  How much
> that is depends
> on how you configured the Linux kernel and how much memory PostgreSQL
> uses.  The latter
> is mostly determined by "shared_buffers", "work_mem",
> "maintenance_work_mem" and
> "max_connections".
>
> On the kernel side, it is mostly the "vm.swappiness" parameter that
> determines how
> eager the kernel is to swap out memory, even if there is no pressure.  For
> best
> performance, that should happen as little as possible, and the database
> should
> determine what to keep in memory and what to store on disk.
>
> One tool you have to prevent shared buffers from being swapped out is to
> define enough
> Linux hugepages, so that PostgreSQL can allocate shared buffers there.
> Linux does not
> swap out hugepages.
>
> You can find the PostgreSQL parameters described in the PostgreSQL
> documentation and the
> kernel parameters in the kernel documentation.
>
> Yours,
> Laurenz Albe
>

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