Re: Online 7.x on IBM uni-processor

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. >Doug > >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. 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. Without CPU cache flushing you will get memory corruption i.e. >1 VP being in a critical section and a time and hence likely database or physical/logical log corruption!! >}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? >}> Yes I belive it may well run slower 7.x is designed to use >1 thread to perform a given SQL statement i.e. to run well on multiprocessor machines. After all multiprocessor machines are moving into the mainstream. I'm amazed that some of my clients who have little money (E.g. many of our clients still use 2400/9600 baud modems and version of Informix and UNIX 5 years out of date [Online 5.00!]). Yet they have 2 CPU machines. Back when I first started using UNIX at University 7/8 years ago multiprocessor machines were only used in computer research and had not moved into the commercial arena. We had an NCUBE 1 with virutally no tools (parallel Fortran 77 only, a C compiler was currently in development), no debugger (one had not been written yet), the OS was not gauarenteed to be stable as we had been told it was still "experimental"! If you have a multiprocessor machine you can use more CPU resources and I suppose assume therefore that more memory is available. You use algorithms which require more CPU power and more memory but run faster as twice (or four times) as much CPU power is available E.g. it require 1.2 seconds of CPU time instead of 1 second but half of the processing can be done on rach of 2 CPUS. It will run faster since 1.2 seconds/number of processors(2) = 0.6 seconds rather then 1 second. Online 7.x is designed to allow this i.e. balances well across CPUS. Also Online 7.x can use things like hash joins which use more memory but can run faster if you have enough memory and CPU power. I would say 7.x with good tuning will be faster but sometimes 5.x will be faster. >}> David Kerslake >}> >}> >}> >} >} >}-- >}Bill Ennis Voice: 312-474-7516 >}SSA Fax: 312-474-7460 >}500 W. Madison email: ennis@ssax.com ennis@accesschicago.net > -- David Williams