Re: [DB2EUG] OVERHEAD and TRANSFERRATE

[Pierrre Saint-Jacques]

These values are used onlly by the optimizer to estimate the I/O workload. If you don't set them and you have your RAID on Fast SCSII or SAN, it's like asking a driver to plan a trip and telling him he's driving a 4 cylinder aluminum block engine.  He'll figure out the right way and plan accordingly, which would not be right, as he and the optimizer don't know better. However, when he comes to drive, he'll use the V8 dual carburator engine anyway, he'll just use it the wrong way! The easiest way to calculate it is to use the Control Center and create a dummy tablespace (you won't create it) and run the wizard to the last page of choices. One page will ask you to specify the type of I/O you have, and I believe there's a choice for RAID, these are general approximations based on current hardware and they should suffice. You then use those values for all tblspcs that will go on the array. After that, the only way you can find out if calculating those values to the second decimal will have any effect, would be to build tblspcs with the different values and benchmark.  In my opinion, I doubt you would see a trmendous change from the choices of the wizard. Given you are on RAID, read the docs. as to container definition and environment variables recommended to be set. HTH,  Pierre. [EMAIL PROTECTED] wrote: Hello,   I would appreciate anything you can share regarding your experiences with calculating and setting your own tablespace OVERHEAD and/or TRANSFERRATE parameters.  Is it worth the bother, or do the default values work well enough?  I am finding the TRANSFERRATE calculation in the Performance Guide to be a little less that clear for RAID arrays, but maybe I am simply having a dense moment.  The calculation for spec_rate in the RAID discussion is what confuses me, as it does not seem to me to include a time measurement.  Also, it would have been helpful if they had given their definition of a small vs. large disk array.   Any thoughts/experiences you can share would be very much appreciated!   Thanks, Judy     -- Pierre Saint-Jacques, IBM Certified Solutions Expert - Administration SES Consultants Inc. 514-737-4515