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From: John Baldwin <jhb@freebsd.org>
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Cc: "hackers@freebsd.org" <hackers@freebsd.org>,
	Doug Barton <dougb@freebsd.org>, Ivan Voras <ivoras@freebsd.org>
Subject: Re: PostgreSQL benchmarks (now with Linux numbers)
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On Wednesday, February 22, 2012 9:59:02 pm Doug Barton wrote:
> On 02/22/2012 01:42, Ivan Voras wrote:
> > The Dragonfly team has recently liberated their VM from the giant lock and there are some interesting benchmarks comparing it to FreeBSD 9 and a 
derivative of RedHat Enterprise Linux:
> > 
> > http://leaf.dragonflybsd.org/mailarchive/kernel/2011-11/msg00008.html
> > 
> > Other developments are described in their release notes: http://www.dragonflybsd.org/release30/
> 
> The 4.5 times improvement by enabling kern.ipc.shm_use_phys is pretty
> notable, what prevents us from enabling that by default?

It makes all your SYSV SHMs wired.  That's fine if you are running a dedicated
server using SYSV SHMs where you want that process to use all the RAM in the
machine (e.g. a pgqsl server).  It's not so great for a general purpose load
where you would like an otherwise-idle process using SYSV SHMs to have the SHMs
paged out to swap if other processes on the machine need memory and the box is
under memory pressure.

-- 
John Baldwin