[PERFORM] Context switching and Xeon processors
We're running a dual Xeon machine with hyperthreading enabled and PostgreSQL 8.0.3. Below is the type of CPUs: processor : 3 vendor_id : GenuineIntel cpu family : 15 model : 4 model name : Intel(R) Xeon(TM) CPU 3.20GHz stepping: 1 cpu MHz : 3200.274 cache size : 1024 KB ... We've been tuning the kernel (2.4 SMP flavor) and have improved performance quite a bit. I'm now wondering if turning off HT will improve performance even more. Based on the vmstat output below, is the context switching typical or too high? And what is the latest on the state of PostgreSQL running on Xeon processors with HT turned on? I searched the archives, but couldn't discern anything definitive. r b swpd free buff cache si sobibo incs us sy wa id 1 0 135944 64612 17136 375681600 0 210 154 178 2 0 4 94 1 0 135940 46600 17204 375449600 1 1231 442 3658 7 3 10 80 1 3 135940 51228 17240 375468000 0 1268 255 2659 4 1 14 81 1 0 135940 58512 17300 375468400 0 1818 335 1526 2 1 32 65 1 1 135940 18104 17328 380651600 17670 476 1314 1962 2 2 41 56 0 1 135940 17776 17232 381162000 23193 394 1600 2097 2 2 53 44 0 1 135940 17944 17188 380963600 25459 349 1547 2013 2 2 50 46 0 3 135940 18816 15184 379831200 24284 1328 1529 4730 6 5 53 36 0 6 135940 23536 6060 381708800 27376 1332 1350 2628 2 3 56 39 0 5 135940 18008 6036 382713200 18806 1539 1410 1416 1 2 61 36 0 5 135940 18492 5708 382666000 3540 10354 736 955 2 2 76 20 0 3 135940 18940 5788 382986400 2308 7506 707 519 2 1 81 15 1 4 135940 18980 5820 382883600 138 3503 556 261 1 0 74 24 0 10 135940 39332 5896 32400 579 2805 621 4104 7 4 54 35 0 4 135936 37816 5952 379140400 260 1887 384 1574 2 1 40 57 0 5 135936 29552 5996 380226000 290 1642 434 1944 3 1 38 58 -- Brandon ---(end of broadcast)--- TIP 6: explain analyze is your friend
Re: [PERFORM] Context switching and Xeon processors
t == [EMAIL PROTECTED] writes: t Brandon Metcalf [EMAIL PROTECTED] writes: t We've been tuning the kernel (2.4 SMP flavor) and have improved t performance quite a bit. I'm now wondering if turning off HT will t improve performance even more. Based on the vmstat output below, is t the context switching typical or too high? t Given that your CPU usage is hovering around 2%, it's highly unlikely t that you'll be able to measure any change at all by fiddling with HT. t What you need to be working on is disk I/O --- the 80% wait number t is what should be getting your attention, not the CS number. t (FWIW, on the sort of hardware you're talking about, I wouldn't worry t about CS rates lower than maybe 1/sec --- the hardware can sustain t well over 10x that.) Yes, I agree the disk I/O is an issue and that's what we've been addressing with the tuning we've been doing and have been able to improve. I think that we really need to go to a RAID 10 array to address the I/O issue, but thought I would investigate the context switching issue. Thanks for the information. -- Brandon ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
Re: [PERFORM] Context switching and Xeon processors
On Tue, Dec 06, 2005 at 03:01:02PM -0600, Brandon Metcalf wrote: We're running a dual Xeon machine with hyperthreading enabled and PostgreSQL 8.0.3. The two single most important things that will help you with high rates of context switching: - Turn off hyperthreading. - Upgrade to 8.1. /* Steinar */ -- Homepage: http://www.sesse.net/ ---(end of broadcast)--- TIP 9: In versions below 8.0, the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
