To optimize performance, you must specify buffer space at OPEN time.
This allows you to tailor the buffer space to suit each particular application and to optimize VSAM performance for the processing that each application performs.
If you calculate that ten index buffers are required to hold the entire index set in storage for a particular file (assume one high level index control interval, eight middle levels, and one sequence set buffer for single string access), you can then modify each and every job stream that accesses this file randomly for optimum performance. Simply specify BUFNI=10 in the AMP parameter on every DD card in every job (test and production) that references this file. These modifications take some time if there are many jobs that access this file, but the end result is optimum performance.
This is static tuning. It works, but you must monitor all of your VSAM files and applications regularly to be sure that performance is optimized. What happens to performance when the file grows to 12 index set records and four index levels? You must go back and adjust all of the BUFNI and BUFND values to reflect the current environment.
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