--- On Mon, 11/4/11, Kevin Grittner <Kevin.Grittner@xxxxxxxxxxxx> wrote: > From: Kevin Grittner <Kevin.Grittner@xxxxxxxxxxxx> > Subject: Re: Linux: more cores = less concurrency. > To: david@xxxxxxx, "Steve Clark" <sclark@xxxxxxxxxxxxx>, "Kevin Grittner" <Kevin.Grittner@xxxxxxxxxxxx>, "Glyn Astill" <glynastill@xxxxxxxxxxx> > Cc: "Joshua D. Drake" <jd@xxxxxxxxxxxxxxxxx>, "Scott Marlowe" <scott.marlowe@xxxxxxxxx>, pgsql-performance@xxxxxxxxxxxxxx > Date: Monday, 11 April, 2011, 22:35 > "Kevin Grittner" <Kevin.Grittner@xxxxxxxxxxxx> > wrote: > > > I don't know why you were hitting the knee sooner than > I've seen > > in my benchmarks > > If you're compiling your own executable, you might try > boosting > LOG2_NUM_LOCK_PARTITIONS (defined in lwlocks.h) to 5 or > 6. The > current value of 4 means that there are 16 partitions to > spread > contention for the lightweight locks which protect the > heavyweight > locking, and this corresponds to your best throughput > point. It > might be instructive to see what happens when you tweak the > number > of partitions. > Tried tweeking LOG2_NUM_LOCK_PARTITIONS between 5 and 7. My results took a dive when I changed to 32 partitions, and improved as I increaced to 128, but appeared to be happiest at the default of 16. > Also, if you can profile PostgreSQL at the sweet spot and > again at a > pessimal load, comparing the profiles should give good > clues about > the points of contention. > Results for the same machine on 8 and 32 cores are here: http://www.8kb.co.uk/server_benchmarks/dblt_results.csv Here's the sweet spot for 32 cores, and the 8 core equivalent: http://www.8kb.co.uk/server_benchmarks/iostat-32cores_32Clients.txt http://www.8kb.co.uk/server_benchmarks/vmstat-32cores_32Clients.txt http://www.8kb.co.uk/server_benchmarks/iostat-8cores_32Clients.txt http://www.8kb.co.uk/server_benchmarks/vmstat-8cores_32Clients.txt ... and at the pessimal load for 32 cores, and the 8 core equivalent: http://www.8kb.co.uk/server_benchmarks/iostat-32cores_100Clients.txt http://www.8kb.co.uk/server_benchmarks/vmstat-32cores_100Clients.txt http://www.8kb.co.uk/server_benchmarks/iostat-8cores_100Clients.txt http://www.8kb.co.uk/server_benchmarks/vmstat-8cores_100Clients.txt vmstat shows double the context switches on 32 cores, could this be a factor? Is there anything else I'm missing there? Cheers Glyn -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
