If he wishes to improve VSAM KSDS performance, increase the buffers and be generous doing it. If that fails to reach your performance target look at using BLSR and allocate enough buffers for the entire index. Also what is your Index CI size? If it is small 512 or 1024 and your Index level is 3, 4 or higher then increase the Index CI size to 4096. That will reduce the level to 1 or 2 thus reducing the path to find your data. I stand to be corrected but the idea that changing extents will flush the buffer is nonsense. Sequential access would also benefits from large allocations of data buffers, eg. bufnd=180 ( assuming a 4k CI size)
________________________________ From: McKown, John [mailto:[EMAIL PROTECTED] Sent: Thu 7/26/2007 12:06 PM To: [email protected] Subject: VSAM in extents I'm curious about this one. A person here has stated that when a VSAM KSDS file is in multiple extents, it performs more poorly than it would in a single contigueous extent. He said something to the effect that when a portion of the index is referenced which is in "another extent" that the entire in-memory buffer for the file is flushed. I have no idea where he got this information. Also, he wants to use SMS striping for VSAM files which are mainly accessed sequentially because it would significantly decrease the I/O time to read. We are using multiple FICON connections to a single 2105 ESS (Shark). We do not have the volumes in any storage group spread across LCUs. My contention is that it may well decrease I/O, but it would require that we likewise stripe the volumes across the 2105's LCUs as well. We don't do this at present. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
