On Wed, Apr 26, 2006 at 06:16:46PM -0400, Bruce Momjian wrote: > Jim C. Nasby wrote: > > On Wed, Apr 26, 2006 at 10:27:18AM -0500, Scott Marlowe wrote: > > > 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 > > > > Or better yet, use dbt* or even pgbench so others can reproduce... > > For why Opterons are superior to Intel for PostgreSQL, see: > > http://techreport.com/reviews/2005q2/opteron-x75/index.x?pg=2 > > Section "MESI-MESI-MOESI Banana-fana...". Specifically, this part about > the Intel implementation: > > The processor with the Invalid data in its cache (CPU 0, let's say) > might then wish to modify that chunk of data, but it could not do so > while the only valid copy of the data is in the cache of the other > processor (CPU 1). Instead, CPU 0 would have to wait until CPU 1 wrote > the modified data back to main memory before proceeding.and that takes > time, bus bandwidth, and memory bandwidth. This is the great drawback of > MESI. > > AMD transfers the dirty cache line directly from cpu to cpu. I can > imaging that helping our test-and-set shared memory usage quite a bit. Wasn't the whole point of test-and-set that it's the recommended way to do lightweight spinlocks according to AMD/Intel? You'd think they'd have a way to make that performant on multiple CPUs (though if it's relying on possibly modifying an underlying data page I can't really think of how to do that without snaking through the cache...) -- Jim C. Nasby, Sr. Engineering Consultant jnasby@xxxxxxxxxxxxx Pervasive Software http://pervasive.com work: 512-231-6117 vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461
