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CICS TS Performance and Tuning: A Rich Tradition


It may sound geeky, but one of my favorite discussion topics—usually limited to a client’s system programmers and sometimes manager—is CICS Transaction Server (TS) performance and tuning. Sysprog is a group I’m very comfortable with, because there aren’t a lot of times I can share an acronym-laden conversation with a bunch of enthusiastic groupies passionate about efficiency.

I joined IBM in 1978 and was immediately assigned to a leading-edge CICS/VS account. Its transaction volume was immense for the time, and because the online system was strained to the very limits of throughput and response time, the IBM CICS development lab in Hursley, England, was very interested in their experience.

I was assigned to take all IBM CICS/VS courses and basic training as soon as possible in Endicott, N.Y., which meant I spent very little time at home, but it was time well spent. I’d present the material I’d been taught with my client—which, due to their superior skills, was like taking the class again on steroids—and simultaneously I brought state-of-the-art CICS information to them. I quickly became very proficient with the transaction server, and while I stayed deeply involved with my client, IBM promoted me to CICS Regional Designated Specialist supporting CICS across the Midwestern U.S. and other locations as needed.

Processor utilization had always been a performance concern, but the biggest performance issue in those days was virtual storage constraint. CICS was still a single address space implementation, so there was no such thing as a terminal-, application- or file-owning region, which would allow CICS function to be spread across multiple regions. Furthermore, MVS was limited to a 24-bit addressing architecture, which limited address space size to 16 megabytes, about half of which was consumed by MVS, VSAM, IMS database and other system software.

Especially for CICS/VS implementations, these virtual storage limitations often created crises, and I found myself making performance visits to one CICS customer after another. CICS could manage storage shortages via a process called program compression, but compressions were very costly in terms of processor utilization, so the analysis had to also address processor consumption. Performance constraints tend to be a cascading process, so virtual storage and processor constraints tend to degradee I/O or data access performance and real storage depletions, often reflected by high paging rates.

Most virtual storage performance and tuning reviews required a broad, all-encompassing investigation that addressed all aspects of processor efficiency, I/O capacity and real storage. Since the truest reflection of performance is response time, some attention would also be given to network configuration and bandwidth, but it was secondary because mainframe was the focus, so network performance was usually assigned to the telecomm staff. Internal mainframe response time, however, was key.

CICS Tuning Checklist

As I continued to conduct performance studies and produce reports that were a combination of observations and recommendations, patterns began to emerge, and over time I developed a standard methodology. Each client had unique characteristics, but there were many items that were typical performance review components. For example, there were usually four areas of investigation:

  1. Virtual storage usage represented by storage compressions in the CICS shutdown statistics
  2. Real storage usage represented by paging rates in SMF records
  3. Processor utilization in SMF records
  4. I/O activity in SMF records

Jim Schesvold can be reached at

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