Re: Online 7.x on IBM uni-processor

At 05:42 PM 9/9/97 +0200, you wrote: }David Williams wrote: }> } > In article <340f0486.1271899725@news.2alpha.com>, Doug Bowman } > <dougb@etcscan.com> writes } > >Bill & David, } > > } > >What about the SINGLE_CPU_VP parameter in the onconfig file? I was } > >told you should also set this to a 1 on a single CPU machine to } > reduce } > >the number of mutex calls. } > > }> Correct but there is still some overhead on 7.x engines since }> internally online must check this parameter each time before }> deciding not to call the mutex. } > > } > >On 3 Sep 1997 10:43:24 -0400, ennis@ssax.com (Bill Ennis) wrote: } > >}Informix version 7 and later is multi-threaded; whch means that it } > >}can take advantage of multiprocessing. } > >} } > >}If you only have one processor you do not want to use the } > >multiprocessing } > >}capabilities. There is overhead involved with multi-threading an } > >operation } > >}since the threads will need to communicate with each other in order } > >to get } > >}the job done. } > >} } > >}Informix recommends that you not use multi-processor mode until } > >}you have a machine that has at least 4 processors. } > >} }> I have not heard the 4 CPUs is the limit. I thought }> MULTIPROCESSOR should be set to 1 i.e. Y when you have >1 CPU. } }The general recommendation is to leave one CPU for 'other' tasks. On a }2 CPU box (I haven't seen any 3 CPU ones :) this leaves you with one }CPU, so switching off the CPU VP locking will reduce the overhead. This }is where the recommendation came from. Of course this also refers to a }single server. If you are setting up a database server, then running 2 }CPU VPs on a 2 CPU box will probably give you better performance than }one, if a) you use PDQ, and b) you fragment tables. } The ODS Performance Guide Ver 7.2 suggests on page 2-11 "On dual-processor systems, you might improve by running with two CPU VPs". In an Informix ODS System Administration Training class last March, our instructor indicated that experience has shown that DataWarehouse systems get better performance by setting NUMCPUVPS to 1 greater than the actual number of available CPUs. When building indexes and updating statistics for fragmented tables we experienced a 60% reduction in elapsed time when using either 2 or 3 NUMCPUVPS on a dual-processor IBM machine. }> After all that it what multiprocessor means, more than one cpu }> and the Online Admin Guide Volume 1 Page 38-41 says }> }> "MULTIPROCESSOR specifies whether Online performs locking in a }> manner that is suitable for a single processor computer or a }> multiprocessor computer". }> }> I assume the differnce it that on a multiprocessor computer }> CPU cache flushing is required to ensure all CPUS maintain a }> consistent view of memory. Sometimes this cache flushing must be }> done explictly in software and I thought that this is what the }> MULTIPROCESSOR parameter is used for. } }I think it's to do with locking queues if you're not the only process }grabbing threads to run. } }Cheers, }-- }Mark. } }+----------------------------------------------------------+-----------+ }|Mark D. Stock - Informix SA http://www.informix.com |//////// /| }|mailto:mdstock@informix.com FAQ http://www.iiug.org |///// / //| }| +-----------------------------------+//// / ///| }| Tel: +27 11 807 0313 |If it's slow, the users complain. |/// / ////| }| Fax: +27 11 807 2594 |If it's fast, the users keep quiet.|// / /////| }|Cell: +27 83 250 2325 |Therefore, "No news: travels fast"!|/ ////////| }+----------------------+-----------------------------------+-----------+ Rick Bernstein Phone: (619) 458-7048 Alaris Medical Systems FAX: (619) 458-7640 San Diego, CA 92121 Internet: rbernste@alarismed.com