On Tue, May 12, 2009 at 8:59 PM, Scott Carey <scott@richrelevance.com> wrote:
> The $ cost of more CPU power on larger machines ends up such a small %
> chunk, especially after I/O cost. Sure, the CPU with HyperThreading and the
> turbo might be 40% more expensive than the other CPU, but if the total
> system cost is 5% more for 15% more performance . . .
But everything dollar I spend on CPUs is a dollar I can't spend on
RAID contollers, more memory, or more drives.
We're looking at machines with say 32 1TB SATA drives, which run in
the $12k range. The Nehalem 5570s (2.8GHz) are going for something in
the range of $1500 or more, the 5540 (2.53GHz) at $774.99, 5520
(2.26GHz) at $384.99, and the 5506 (2.13GHz) at $274.99. The 5520 is
the first one with hyperthreading so it's a reasonable cost increase.
Somewhere around the 5530 the cost for increase in performance stops
making a lot of sense.
The opterons, like the 2378 barcelona at 2.4GHz cost $279.99, or the
2.5GHz 2380 at $400 are good values. And I know they mostly scale by
clock speed so I can decide on which to buy based on that. The 83xx
series cpus are still far too expensive to be cost effective, with
2.2GHz parts running $600 and faster parts climbing VERY quickly after
that.
So what I want to know is how the 2.5GHz barcelonas would compare to
both the 5506 through 5530 nehalems, as those parts are all in the
same cost range (sub $500 cpus).
> It depends on how CPU limited you are. If you aren't, there isn't much of a
> reason to look past the cheaper Opterons with a good I/O setup.
Exactly. Which is why I'm looking for best bang for buck on the CPU
front. Also performance as a "data pump" so to speak, i.e. minimizing
memory bandwidth limitations.
> I've got a 2 x 5520 system with lots of RAM on the way. The problem with
> lots of RAM in the Nehalem systems, is that the memory speed slows as more
> is added.
I too wondered about that and its effect on performance. Another
benchmark I'd like to see, how it runs with more and less memory.
> I think mine slows from the 1066Mhz the processor can handle to
> 800Mhz. It still has way more bandwidth than the old Xeons though.
> Although my use case is about as far from pg_bench as you can get, I might
> be able to get a run of it in during stress testing.
I'd be very interested in hearing how it runs. and not just for pgbench.
