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Re: Large (8M) cache vs. dual-core CPUs

From: Scott Marlowe <smarlowe(at)g2switchworks(dot)com>
To: mark(at)mark(dot)mielke(dot)cc
Cc: Bill Moran <wmoran(at)collaborativefusion(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Large (8M) cache vs. dual-core CPUs
Date: 2006-04-26 15:27:18
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Lists: pgsql-performance
On Tue, 2006-04-25 at 20:17, mark(at)mark(dot)mielke(dot)cc wrote:
> On Tue, Apr 25, 2006 at 08:54:40PM -0400, mark(at)mark(dot)mielke(dot)cc wrote:
> > I made the choice I describe based on a lot of research. I was going
> > to go both Intel, until I noticed that the Intel prices were dropping
> > fast. 30% price cut in 2 months. AMD didn't drop at all during the
> > same time.
> Errr.. big mistake. That was going to be - I was going to go both AMD.
> > There are plenty of reasons to choose one over the other. Generally
> > the AMD comes out on top. It is *not* 2X though. Anybody who claims
> > this is being highly selective about which benchmarks they consider.
> I have an Intel Pentium D 920, and an AMD X2 3800+. These are very
> close in performance. The retail price difference is:
>     Intel Pentium D 920     is selling for $310 CDN
>     AMD X2 3800+            is selling for $347 CDN

Let me be clear.  The performance difference between those boxes running
the latest first person shooter is not what I was alluding to in my
first post.  While the price of the Intel's may have dropped, there's a
huge difference (often 2x or more) in performance when running
PostgreSQL on otherwise similar chips from Intel and AMD.

Note that my workstation at work, my workstation at home, and my laptop
are all intel based machines.  They work fine for that.  But if I needed
to build a big fast oracle or postgresql server, I'd almost certainly go
with the AMD, especially so if I needed >2 cores, where the performance
difference becomes greater and greater.

You'd likely find that for PostgreSQL, the slowest dual core AMDs out
would still beat the fasted Intel Dual cores, because of the issue we've
seen on the list with context switching storms.

If you haven't actually run a heavy benchmark of postgresql on the two
architectures, please don't make your decision based on other
benchmarks.  Since you've got both a D920 and an X2 3800, that'd be a
great place to start.  Mock up some benchmark with a couple dozen
threads hitting the server at once and see if the Intel can keep up.  It
should do OK, but not great.  If you can get your hands on a dual
dual-core setup for either, you should really start to see the advantage
going to AMD, and by the time you get to a quad dual core setup, it
won't even be a contest.

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