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

From: William Yu <wyu(at)talisys(dot)com>
To: pgsql-performance(at)postgresql(dot)org
Subject: Re: Large (8M) cache vs. dual-core CPUs
Date: 2006-04-26 14:19:38
Message-ID: e2nvhj$1h3b$1@news.hub.org (view raw or flat)
Thread:
Lists: pgsql-performance
mark(at)mark(dot)mielke(dot)cc wrote:
> 
> 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
> 
> Anybody who claims that Intel is 2X more expensive for the same
> performance, isn't considering all factors. No question at all - the
> Opteron is good, and the Xeon isn't - but the original poster didn't
> ask about Opeteron or Xeon, did he? For the desktop lines - X2 is not
> double Pentium D. Maybe 10%. Maybe not at all. Especially now that
> Intel is dropping it's prices due to overstock.

There's part of the equation you are missing here. This is a PostgreSQL 
mailing list which means we're usually talking about performance of just 
this specific server app. While in general there may not be that much of 
a % difference between the 2 chips, there's a huge gap in Postgres. For 
whatever reason, Postgres likes Opterons. Way more than Intel 
P4-architecture chips. (And it appears way more than IBM Power4 chips 
and a host of other chips also.)

Here's one of the many discussions we had about this issue last year:

http://qaix.com/postgresql-database-development/337-670-re-opteron-vs-xeon-was-what-to-do-with-6-disks-read.shtml

The exact reasons why Opteron runs PostgreSQL so much better than P4s, 
we're not 100% sure of. We have guesses -- lower memory latency, lack of 
shared FSB, better 64-bit, 64-bit IOMMU, context-switch storms on P4, 
better dualcore implementation and so on. Perhaps it's a combination of 
all the above factors but somehow, the general experience people have 
had is that equivalently priced Opterons servers run PostgreSQL 2X 
faster than P4 servers as the baseline and the gap increases as you add 
more sockets and more cores.

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