Author: Ronald K. Ferguson Co-Author: Elliot Hamilton

Synopsis
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This book is the first, complete reference work, to cover in one volume the entire topic of the Virtual Storage Access Method (VSAM) used with OS/390 operating systems. Its purpose is to explain in plain English, yet, in considerable technical depth, how to create and maintain VSAM files. It presents all aspects of VSAM, including complete file structures of ESDS, RRDS, KSDS, and LDS files, as well as extended format VSAM files. The Access Method Services (IDCAMS) utility program used to define and maintain VSAM files is also covered in depth, as well as support for ICF catalogs.

Considerable effort was spent in writing this book to debunk many of the myths about how VSAM files, particularly KSDS files, should be defined and maintained. Of particular importance is the chapter on CI and CA splits, how FREESPACE actually works (and when, and how much - if any - you should specify). Recommendations on reducing the frequency of file reorganizations will enable you to squeeze better performance from your file's processing, contrary to the popular belief that more-frequent re-orgs improve performance. In many instances, the technical details about how to properly specify DEFINE command parameters is in conflict with the IBM manuals, even the published IBM Redbook, VSAM Demystified, but the information in Mainstar's book is definitely more accurate and correct. Our work with VSAM Manager, a VSAM tuning product from Mainstar, has provided information about how VSAM files actually behave in the 'real world', that even IBM does not understand. This book is an absolute must if you are trying to maximize performance and DASD utilization of your VSAM files.