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Date: Wed, 24 May 2006 08:34:51 +0200
From: "Claus Guttesen" <kometen@gmail.com>
To: "Mark Kirkwood" <markir@paradise.net.nz>
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Cc: freebsd-stable@freebsd.org
Subject: Re: PostgreSQL uses more memory on 6.1?
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> > That did it!  Bumping kern.ipc.shmall to 65536 got me back up and runni=
ng
> > with enough shared_memory to get my jobs done.
>
> Having not so long ago been caught by this myself, I think the
> relationship between shmmax and shmall is worth clarifying:
>
> $ sysctl -d kern.ipc.shmall
> kern.ipc.shmall: Maximum number of pages available for shared memory
> $ sysctl -d kern.ipc.shmmax
> kern.ipc.shmmax: Maximum shared memory segment size
>
> So to run 1 Postgres installation with 128Mb of shared memory:
>
> kern.ipc.shmall=3D32768
> kern.ipc.shmmax=3D134217728
>
> However suppose you want to run 2 Postgres installations, each using
> 128Mb of shared memory:
>
> kern.ipc.shmall=3D65536
> kern.ipc.shmmax=3D134217728
>
> i.e. maximum system wide shared memory is 65536*4096 =3D 256Mb, but the
> maximum size any single segment can be is 128Mb.

Thank you. I wasn't aware that one could alter sysctl's. I might dive
into that, makes kernel-maintenance a tiny bit easier.

regards
Claus