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Re: icps, shmmax and shmall - Shared Memory tuning

From: "Arsalan Zaidi" <azaidi(at)directi(dot)com>
To: <pgsql-general(at)postgresql(dot)org>
Subject: Re: icps, shmmax and shmall - Shared Memory tuning
Date: 2002-04-29 09:04:04
Message-ID: 012101c1ef5c$d418a860$4301a8c0@directi.com (view raw or flat)
Thread:
Lists: pgsql-general
----- Original Message -----
From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Martijn van Oosterhout <kleptog(at)svana(dot)org>
Cc: dorian dorian <dorian37076(at)yahoo(dot)com>; <pgsql-general(at)postgresql(dot)org>
Sent: Monday, April 29, 2002 9:17 AM
Subject: Re: [GENERAL] icps, shmmax and shmall - Shared Memory tuning


> Martijn van Oosterhout <kleptog(at)svana(dot)org> writes:
> > On Sun, Apr 28, 2002 at 08:12:56PM -0400, Tom Lane wrote:
> >> Sane kernels return an error on sbrk(2) if they don't have any more
> >> memory to give out...
>
> > The problem is that sbrk merely extends your memory map, the memory is
not
> > actually allocated until it is used, i.e. it's overcomitting memory.
>
> And this is the application's fault?
>
> If Linux overcommits memory, then Linux is broken.  Do not bother to
> argue the point.

IANAKH, but I believe Linux chooses to over-commit cause many programs asks
for far more RAM than they ever use. It's a bit of a gamble for the kernel
to allow
memory overcommit, but it pays off most of the time.

I think you can turn it off by placing the line

vm.overcommit_memory = 0

in /etc/sysctl.conf

--Arsalan.



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