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Date: Wed, 24 May 2006 12:51:03 +1200
From: Mark Kirkwood <markir@paradise.net.nz>
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To: Kirk Strauser <kirk@strauser.com>
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Cc: freebsd-stable@freebsd.org
Subject: Re: PostgreSQL uses more memory on 6.1?
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Kirk Strauser wrote:
> On Tuesday 23 May 2006 16:19, Jung-uk Kim wrote:
> 
>> I meant 'kern.ipc.shmall', which used to be 'kern.ipc.shmmaxpgs'. :-(
> 
> That did it!  Bumping kern.ipc.shmall to 65536 got me back up and running 
> 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=32768
kern.ipc.shmmax=134217728

However suppose you want to run 2 Postgres installations, each using 
128Mb of shared memory:

kern.ipc.shmall=65536
kern.ipc.shmmax=134217728

i.e. maximum system wide shared memory is 65536*4096 = 256Mb, but the 
maximum size any single segment can be is 128Mb.

Cheers

Mark