Re: Postgres database performance on 6 core Opteron vs 4 core Xeon

Postgres User wrote:
> The 6 core processor should offer a clear edge but these AMD
> processors are cited for relatively slow L3 cache speeds compared to
> their Intel counterparts.
>
The big problem is that the raw memory speed in the Intel Nehelem
designs (with 3-channel DDR3 1333MHz) is so superior to AMD's right now
(dual-channel DDR2-800) that even two extra cores can't pull them ahead
in a lot of tasks. And Intel's hyperthreading support on the new
processors is really effective, so you're actually evaluating an 8-core
Intel solution vs. a 6-core AMD one. Take a look at
http://it.anandtech.com/IT/showdoc.aspx?i=3571&p=5 for example, which is
a pretty realistic database benchmarking app where AMD gets spanked.

At this point, the new Opterons close a lot of gap against Intel's
designs, but the gap is still there. It can be easy to justify AMD
purchases anyway on a cost/power basis, as Intel's stuff is still
expensive and might run hotter for some workloads. But make no
mistake: if you want the best possible performance without going
completely crazy price-wise, Intel still owns that category, for one or
two processor installs at least. Some of AMD's redesign aims to help in
larger servers with 4 processors instead, the "HT Assist" feature. See
http://arstechnica.com/hardware/news/2009/06/they-might-be-profitable-amds-six-core-istanbul-reviewed.ars
for an intro. I'm not optimistic for AMD here though either. By the
time we start seeing those, Intel will have their Nehalem-EX chips out,
which given Intel's track record I expect will return them to crushing
AMD at the high-end again.

Returning to the real world of database performance, every dollar spent
on your processors and expensive memory is one you can't spend on disks
instead, so in reality AMD's cost effectiveness can make for a better
overall database system at the same price point. If you really need a
lot of disks to make your app performance well, better to focus on that
rather than trivia like how fast stuff moves around the memory bus.

--
Greg Smith 2ndQuadrant Baltimore, MD
PostgreSQL Training, Services and Support
greg(at)2ndQuadrant(dot)com www.2ndQuadrant.com