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 gsmith@xxxxxxxxxxxxx http://www.gregsmith.com Baltimore, MD -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
