>>> tps = 9818.741060 (including connections establishing) >>> >>> So I thought I could squeeze 10000 TPS from my box. >>> Then I tried with -R 5000 tps. >>> >>> number of transactions actually processed: 1510640 >>> average rate limit lag: 0.304 ms (max 19.101 ms) >>> tps = 5035.409397 (including connections establishing) >>> >>> As you can see, I got about 5000 tps as expected. > > Yep, it works:-) > >>> But I'm confused by the lag: >>> >>> 0.304 ms * 1510640 = 459.2 seconds, which is longer than 300 seconds >>> (specified by -T). Am I missing something? > > The lag is reasonnable, althought no too good. One transaction is > about 1.2 ms, the lag is much smaller than that, and you are at about > 50% of the maximum load. I've got similar figures on my box for such > settings. It improves if your reduce the number of clients.
No, 5000 TPS = 1/5000 = 0.2 ms per transaction, no? However pgbench says average lag is 0.304 ms. So the lag is longer than transaction itself. > If you reduce the number of clients, or add more threads, the lag is > reduced. > >> BTW, the system was Linux (kernel 3.0.77). > >> tps = 6730.940132 (including connections establishing) >> $ pgbench -S -n -c 10 -T 10 -R 3000 test > >> average rate limit lag: 0.089 ms (max 27.301 ms) >> tps = 2983.707895 (including connections establishing) >> >> 0.089 ms * 29840 = 2.66 seconds. Not too bad compared with 10 >> seconds. > > Indeed, that is better. Transactions are about 1.5 ms and you run at > about 45% of the maximum load here. > >> On Linux maybe the overhead to calculate the lag is bigger >> than Mac OS X? Just my wild guess though... > > I would be surprised that this would be the issue is to compute the > measure, compared to network connections and the like. With -S the > bench is cpu bound. Possibly a better scheduler/thread management on > OSX? Or more available cores? The number of cores is same. I don't understand why number of cores is relatedx, though. Anyway, as you can see in Mac OS X's case, TPS itself is no better than the Linux box. > Well, I do not know! At high load with > clients running on the same box as the server, and with more clients & > server than available cores, there is a lot of competition between > processes, and between clients that share a unique thread, and a log > context switching whoch will result in a measured lag. Hmm... I would like to have cleaner explanation/evidence before committing the patch. -- Tatsuo Ishii SRA OSS, Inc. Japan English: http://www.sraoss.co.jp/index_en.php Japanese: http://www.sraoss.co.jp -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers