Re: Online 7.x on IBM uni-processor

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. > > The parameter in the onconfig file you need to be concerned with > is MULTIPROCESSOR (set it to 0). You should also set NUMCPUVPS=1. > > I would think that you would expect a multi-processor machine to perform > better than a single CPU machine so I wouldn't call that performance > degradation. > > -Bill > > > > We are running Informix systems on IBM RS6000s under AIX 4.2. We have to > > upgrade to Informix DSA v7.x to take advantage of the latest release of > > our application. > > > > We have heard that DSA, written for multi-processors, runs slower on a > > uni-processor (which is what we have). Has anyone any information on > > any potential performance degradation? > > > > David Kerslake > > > > > > > > -- > Bill Ennis Voice: 312-474-7516 > SSA Fax: 312-474-7460 > 500 W. Madison email: ennis@ssax.com ennis@accesschicago.net Hi Bill and David I run a IBM rs/6000 R24 single processor machine for almost 2 years now using DSA version 7.1[023] successively. We run a 24x7 operation with online voice response units serving 300 telephone lines during 07:00 - 02:00 and doing batch processing in the nights. We have a reasonable good performance on a 20 Gb database of which I must say is well tuning in respect to disk oparation, placing, fragmenting a.s.o.. We also evaluate runtime results (various onstat outputs) on a weekly basis, tuning as need arises because the application and database requirements change from time to time. When I compare this machine to other customers HP and Unisys 6000 machines that really use multiprocessors, I observe the following differences: - The single CPU IBM machine tends to be more CPU bound - We get on the average more io's done per second in the multi cpu machines because we either have more cpu vp's doing kernel IO or in another installation doing more aio vp's on multiple chunks. I know DSA involves some overhead as compared to OnLine 5 but I really am quite satisfied using DSA 7.12 on a single CPU. Note: The R24 is the fastest RS/6000 cpu curently available. Migrating to the R30 with 4 cpu's will give you NO cpu power increase - according to the IBM salesman - because these processors are slower and due to OS overhead. But you may sure benefit from parallelism even if your application is (mostly) single threaded. I am always open to iscussion on this topic. Gert van Eck DBA Nederland BV The Netherlands gvaneck@worldaccess.nl