Обсуждение: Querry and SMP mechine
Hello Im using postgres 8.0.1 on Debian Sarge with 2 XEON 2.4 HT. doing cat /etc/cpuinfo shows that linux sees 4 cpu ( the HT effect ). I noticed that when im runing a big query only one of the CPUs become loaded. Is it normal behavior ? am i missing something ? Thanks -- -------------------------- Canaan Surfing Ltd. Internet Service Providers Ben-Nes Michael - Manager Tel: 972-4-6991122 Cel: 972-52-8555757 Fax: 972-4-6990098 http://www.canaan.net.il --------------------------
On Sun, Aug 07, 2005 at 01:04:51PM +0300, Michael Ben-Nes wrote: > Hello > > Im using postgres 8.0.1 on Debian Sarge with 2 XEON 2.4 HT. > > doing cat /etc/cpuinfo shows that linux sees 4 cpu ( the HT effect ). > > I noticed that when im runing a big query only one of the CPUs become > loaded. > > Is it normal behavior ? am i missing something ? Yep, PostgreSQL uses a single backend for each client, so if you want to use all four processors, you need to be running four queries simultaneously... Have a nice day, -- Martijn van Oosterhout <kleptog@svana.org> http://svana.org/kleptog/ > Patent. n. Genius is 5% inspiration and 95% perspiration. A patent is a > tool for doing 5% of the work and then sitting around waiting for someone > else to do the other 95% so you can sue them.
Вложения
> Im using postgres 8.0.1 on Debian Sarge with 2 XEON 2.4 HT. > > doing cat /etc/cpuinfo shows that linux sees 4 cpu ( the HT effect ). > > I noticed that when im runing a big query only one of the > CPUs become loaded. > > Is it normal behavior ? am i missing something ? Yes, that is normal. Only one CPU per concurrent query is used. If your load is mostly single or dual sessions runinng queries, you will probably get a better performance if you disable hyperthreading. If you normally have a lot of concurrent sessions, HT will probably help your total performance. //Magnus
Martijn van Oosterhout wrote: >On Sun, Aug 07, 2005 at 01:04:51PM +0300, Michael Ben-Nes wrote: > > >>Hello >> >>Im using postgres 8.0.1 on Debian Sarge with 2 XEON 2.4 HT. >> >>doing cat /etc/cpuinfo shows that linux sees 4 cpu ( the HT effect ). >> >>I noticed that when im runing a big query only one of the CPUs become >>loaded. >> >>Is it normal behavior ? am i missing something ? >> >> > >Yep, PostgreSQL uses a single backend for each client, so if you want >to use all four processors, you need to be running four queries >simultaneously... > > You mean select 1, select 2 & sleect 3 will run on the same cpu becouse they submited from the same PSQL session ? Or each select will be run in turn on the most idle cpu ? Is this true for all the other OS or just for Linux ? (Bsd, solaris... ) Thanks >Have a nice day, > > -- -------------------------- Canaan Surfing Ltd. Internet Service Providers Ben-Nes Michael - Manager Tel: 972-4-6991122 Cel: 972-52-8555757 Fax: 972-4-6990098 http://www.canaan.net.il --------------------------
On Sun, Aug 07, 2005 at 02:15:50PM +0300, Michael Ben-Nes wrote: > >Yep, PostgreSQL uses a single backend for each client, so if you want > >to use all four processors, you need to be running four queries > >simultaneously... > > > > > You mean select 1, select 2 & sleect 3 will run on the same cpu becouse > they submited from the same PSQL session ? > Or each select will be run in turn on the most idle cpu ? No, they are run in the same single process and run on one cpu. The OS can ofcourse shift it to whichever CPU it thinks is most appropriate. It can shift it in the middle of a query too, but that's not up to PostgreSQL. > Is this true for all the other OS or just for Linux ? (Bsd, solaris... ) A single client uses a single CPU at a time, but it's not tied to that particular CPU. That applies to all supported platforms... Have a nice day, -- Martijn van Oosterhout <kleptog@svana.org> http://svana.org/kleptog/ > Patent. n. Genius is 5% inspiration and 95% perspiration. A patent is a > tool for doing 5% of the work and then sitting around waiting for someone > else to do the other 95% so you can sue them.