> -----Original Message----- > From: IBM Mainframe Discussion List [mailto:[email protected]] On > Behalf Of Don Higgins > Sent: Saturday, December 19, 2009 7:24 AM > To: [email protected] > Subject: Re: 360 programs on a z/10 <Snipped> > Anyway I remember studying the channel programs used by ISAM and > although they were designed to maximize I/O speed, they were severely > hampered by the lack of VSAM CA/CI indexing which resulted in exceedly > long sequential chains of overflow records which could runs for hours > if the file was not unloaded and reloaded to restore evenly > distributed overflow track space.
Which was why in the day I remember sorting input batch files in reverse (descending) key sequence so that the ISAM I/O would find the "next" insertion point without traversing the entire overflow chain. Ideally, if the "next" point was at the start of an overflow chain, *none* of the chain had to be read to do the next insertion. Ah yes, those were the days... (not!). Peter This message and any attachments are intended only for the use of the addressee and may contain information that is privileged and confidential. If the reader of the message is not the intended recipient or an authorized representative of the intended recipient, you are hereby notified that any dissemination of this communication is strictly prohibited. If you have received this communication in error, please notify us immediately by e-mail and delete the message and any attachments from your system. ---------------------------------------------------------------------- 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
