On Tue, 28 Jul 2009, Scott Marlowe wrote:

Just FYI, I ran the same basic test but with -c 10 since -c shouldn't
really be greater than -s

That's only true if you're running the TPC-B-like or other write tests, where access to the small branches table becomes a serious hotspot for contention. The select-only test has no such specific restriction as it only operations on the big accounts table. Often peak throughput is closer to a very small multiple on the number of cores though, and possibly even clients=cores, presumably because it's more efficient to approximately peg one backend per core rather than switch among more than one on each--reduced L1 cache contention etc. That's the behavior you measured when your test showed better results with c=10 than c=16 on a 8 core system, rather than suffering less from the "c must be < s" contention limitation.

Sadly I don't have or expect to have a W5580 in the near future though, the X5550 @ 2.67GHz is the bang for the buck sweet spot right now and accordingly that's what I have in the lab at Truviso. As Merlin points out, that's still plenty to spank any select-only pgbench results I've ever seen. The multi-threaded pgbench batch submitted by Itagaki Takahiro recently is here just in time to really exercise these new processors properly.

--
* Greg Smith gsm...@gregsmith.com http://www.gregsmith.com Baltimore, MD

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