The only questions would be:
(1) Do you need a SMP server at all? I'd claim yes -- you always need 2+ cores whether it's DC or 2P to avoid IO interrupts blocking other processes from running.

I would back this up. Even for smaller installations (single raid 1, 1 gig of ram). Why? Well because many applications are going to be CPU bound. For example we have a PHP application that is a CMS. On a single CPU machine, RAID 1 it takes about 300ms to deliver a single page, point to point. We are not IO bound. So what happens is that under reasonable load we are actually waiting for the CPU to process the code.

A simple upgrade to an SMP machine literally doubles our performance because we are still not IO bound. I strongly suggest that everyone use at least a single dual core because of this experience.

(3) Do you need an insane amount of memory? Well here's the case where the more expensive motherboard will serve you better since each CPU slot has its own bank of memory. Spend more money on memory, get cheaper single-core CPUs.
Agreed. A lot of times the slowest dual-core is 5x what you actually need. So get the slowest, and bulk up on memory. If nothing else memory is cheap today and it might not be tomorrow.

Of course, this doesn't apply if you are an Intel/Dell-only shop. Xeon DCs, while cheaper than their corresponding single-core SMPs, don't have the same performance profile of Opteron DCs. Basically, you're paying a bit extra so your server can generate a ton more heat.

Well if you are an Intel/Dell shop running PostgreSQL you have bigger problems ;)


Joshua D. Drake

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