Re: SMP and 7.x performance questions?

Everyone keeps repeating Round Robin is not a Good Fragmentation Method. Well in my Class I was told different. So, Before I start this process could someone give me the Good, Bad and Ugly of using Round Robin. ------------------------------------------------------------------------- Cheryl Kendricks Internet: cherylk@spamis.jcdc.doleta.gov OR cherylk@prod1.jcdc.doleta.gov OR kendric@gwysmtp.jcdc.doleta.gov DTSI, Inc. Voice: 1-800-598-5008 Database Adminstrator - DOL Job Corps San Marcos, Texas ------------------------------------------------------------------------ On Fri, 8 Mar 1996, Jim Gordon wrote: } On Mar 8, 5:28pm, Fernando Fernandez wrote: } > Subject: Re: SMP and 7.x performance questions? } > Dave Kosenko wrote: } > > A small SMP is a bit problemmatic, though. For some reason, it gets hard } to } > > load balance across only 2 cpus. For those in such a situation, I } recommend } > > trying to tun the system as though it were a uniprocessor (set the } SINGLE_CPU } > > parameter on). This introduces some optimizations through the code stream } > > (avoids doing things that are only pertinant in a multi-proc environment) } > > that can help. Once you are 4 procs or better, though, you are better off } > > tuning for SMP. } > } > I already heard in several places that SMP will only work well up to 8 CPU. } > If this theory is correct, we should only use SMP with 4 to 8 CPU's, then } > start with MPP loosely-coupled architectures. } } This somewhat depends on the actual box. It varys between 8 and 32 I expect } depending on manufacturer. } } > } > Now back to Informix... This 7.1 performance problem in few CPU machines } > raises another question: should we use disk fragmentation in those cases? } > I believe this must be considered carefully because disk fragmentation is } > strongly dependent on parallel execution. } > } > For example: I think that round robin fragmentation is not worth with low } > number of CPU's, but hashing is a good policy because of the method of } > skipping fragments. } } Round Robin is almost never a good idea as it really doesn't really provide } benefits just a whole host of performance problems. Well thats my opinion } anyway! } } But fragmentation isn't used only for parrallelism. You can use it to stop a } query from accessing multiple fragments. This means that you can cut the } number of index level searches you need to find a row. This works even on } single cpu boxes. } } As the engine is threaded you should see benefit from fragmentation even on } boxes with only 2 cpus if the query is complex enough. You might even see } benefit on a single cpu box as the engine may use it's thread capability to } switch fragment search threads when one becomes I/O blocked. } } Cheers - Jim } } -- } ----------------------------------------------------------------------------- } Jim Gordon DHL Airways Inc. jgordon@us.dhl.com } ----------------------------------------------------------------------------- } My opinions are my own. They may vary with time but they remain mine! }