From: Greg Smith <gsmith@gregsmith.com>
To: pgsql-performance@postgresql.org
Subject: Re: Dual core Opterons beating quad core Xeons?
Date: Wed, 19 Dec 2007 15:31:22 -0500 (EST)
Message-ID: <Pine.GSO.4.64.0712191444360.29520@westnet.com> (raw)
In-Reply-To: <fkbqho$1jsp$1@news.hub.org>
References: <476908BB.5090408@stuartbishop.net>
<Pine.GSO.4.64.0712191322410.29296@westnet.com>
<20071219105921.07b45a36@commandprompt.com>
<fkbqho$1jsp$1@news.hub.org>
On Wed, 19 Dec 2007, Ron Mayer wrote:
> Benchmarks I see[1] suggest that 8.1.2 scaled pretty reasonably to 16
> cores (from the chart on page 9 in the link below). But yeah, 8.0
> scaled to maybe 2 cores if you're lucky. :-)
> [1] http://www.pgcon.org/2007/schedule/attachments/22-Scaling%20PostgreSQL%20on%20SMP%20Architectures%20...
Thank you, I was looking for that one but couldn't find it again. Note
that those results are using a TPC-C variant, which is not the most CPU
intensive of tests out there. It's certainly possible that an application
that has more processing to do per transaction (I'm thinking something
more in the scientific computing database realm) could scale even better.
While I'd expect the bang per buck to go down quite a bit beyond 8 cores,
I know I haven't seen any data on what new systems running 8.3 are capable
of, and extrapolating performance rules of thumb based on old data is
perilous. Bottlenecks shift around in unexpected ways. In that Unisys
example, they're running 32-bit single core Xeons circa 2004 with 4MB of
*L3* cache and there's evidence that scales >16 processors. Current Xeons
are considerably faster and you can get them with 4-8MB of *L2* cache.
What does that do to scalability? Beats me. Maybe since the individual
CPUs are faster, you bottleneck on something else way before you can use
16 of them usefully. Maybe the much better CPU cache means there's less
reliance on the memory bus and they scale better. It depends a lot on the
CPU vs. memory vs. disk requirements of your app, which is what I was
suggesting before.
--
* Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD
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To: pgsql-performance@postgresql.org
Cc: gsmith@gregsmith.com
Subject: Re: Dual core Opterons beating quad core Xeons?
In-Reply-To: <Pine.GSO.4.64.0712191444360.29520@westnet.com>
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