Re: Two Instances on Multiple CPU Machine

Think of it this way, if any single instance has enough simultaneous requests that it must queue them up until the CPU VP can get around to them, then Informix will do better with an additional CPU VP on any decent SMP box. Although the Informix affinity settings might take some tweaking, in general, if instance 1 is idle, it will yield the processor to istance 2. We currently run 4 instances on our development box with 8 CPUs. Instances 1 is for development and can make due with 1 CPU VP. Instances 2 and 3 are for different applications training and we give them between 2 and 4 CPU VPs as the training schedule changes. Instance 4 is a full blown copy of the 230 GB production system for heavy integration and stress testing. It gets 6 CPU VPs most all the time. So you see, there is some overflow. BTW, on our NCR platform, OS level affinity means the process will "prefer" to stay with a specific processor but is free to move to an available one if the preferred one is unavailable. This helps optimize caching, stack space, and registers. Also, on the NCR box, Informix's AFFINITY settings imply "binding" processes to processors. This could get ugly if there are times when the app needs priority and Informix is idle. With binding, everyone plays second fiddle to the bound process. I hope this helps you. Take care. +--------------------------------------------------------------------------- -------------------------------------+ Chuck Ludwigsen <cludwigs@hotmail.com> Database Engineer, Harrahs Entertainment, Inc. <cludwigsen@harrahs.com> President, Memphis Informix User's Group <miug@hotmail.com> My opinions are my own and sometimes disagree with those of my company. And that's probably a good thing. +--------------------------------------------------------------------------- -------------------------------------+ Madan Mashalkar <madan@infogain.com> wrote > > Hi , > > I have a quick couple of questions. > > We have a SUN machine with SUNOS having 4 CPUs. There is already > one instance of Informix(7.2x) up-and-running which uses 2 cpus (1 and 2) > by setting AFF_SPROC etc and all other parameters. The second instance > of Informix has been configured to use CPU number 3. There is also > an MRP application running, so we figured, we might leave one CPU for > that application. > > Now the question. Can we get any performance improvement/degradation > if we configure our second Informix instance to use say, two CPUs ? > > Also if both instances are configured to run on say, three CPUs > each, will there be any positive/negative impact ? What would be the > optimum allocation (of CPUs) in the above scenario ? > > Thanks > > Madan