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Get Started With CICS Performance and Tuning


The distributed network of interconnected CICS’s imposed a significant expansion of tuning methods and techniques for systems programmers or administrators, because each platform is constructed somewhat differently. Tuning takes different forms like program caching, reducing remote procedure call registrations and shared class caching, and common tuning tasks like migration to new releases, optimizing dataset layout, parameter optimization, tuning buffer pools and threads/sessions/connections (logical portals between network CICS nodes). CICS has become an all-platform OLTP environment, and so has its tuning.

Categories of CICS Tuning

CICS or any IT tuning methodology is hardly a static matter. Since the very early days of CICS, tuning the most widely used and dominant product in the history of IT has been an evolving discipline that changes with product and technology.

CICS tuning’s history provides a valuable starting point for performance enhancement, because the progression of tuning tasks and categories is a list of items that may be relevant for implementation if they’re germane to the performance study’s objectives. The specific tasks listed below are examples, a subset of all tuning tasks:

First-generation tuning, processor and real storage constraints:

  • Optimize CICS processor utilization via System Initialization Table parameters, MVS dispatching priority and other techniques
  • Review real storage usage and allocate as much as possible to CICS
  • Review startup options in general
  • Upgrade to a faster computer if possible
  • Modify applications to remove CPU-intensive function where possible. Modifying applications is a last-ditch effort due to effort and complexity.

Second-generation tuning, DASD and I/O constraints:

  • Evaluate data set layout, channel transfer, utilization, disk rotation time and. most important, buffering. Balance data activity via dataset relocation and movement, reorganize datasets to optimize I/O.
  • Increase CICS buffer allocations, monitor impact on virtual and real storage
  • Use VSAM Shared Buffers
  • Validate region sizes to make optimum use of virtual storage

Third-generation tuning, paging performance constraints:

  • Evaluate page data set layout, reorganize to minimize contention
  • Modify CICS parameters
  • Split CICS systems to spread activity across TCBs if possible. This is a difficult undertaking due to resource sharing requirements.
  • Add real storage if possible to reduce paging

Fourth-generation tuning, virtual storage constraints:

  • Split CICS Regions
  • Optimize DSA settings

Fifth-generation tuning, network throughput and connectivity constraints:

  • Identify network bottlenecks and add capacity or reconfigure traffic
  • Add CICS sessions between nodes (e.g., mainframe and downstream TXSeries)

Sixth-generation tuning, WLM configuration constraints:

  • Compare job performance to WLM settings, modify to prioritize high priority work
  • Increase importance of tasks locking resources to improve resource availability

Seventh-generation tuning, CICS web processing constraints:

  • Optimize mainframe CICS web processing via internal parameters
  • Upgrade TXSeries to newest release, tune program caching in downstream nodes

What’s Next?

Performance information needs to be gathered to determine where bottlenecks and excessive resource consumption exist, what factors curtail response time, what priorities and performance objectives are being missed, and what constraints listed above might need tuning. Drilling down reveals options which may resolve performance issues; they need to be prioritized, vetted and tested. The process has begun. Care needs to be taken in moving changes to production. Change control dictates timing, and backout procedures need definition. Measurement criteria need to be established and data collected to determine impact and for comparison purposes.

A Moving Target

The progression I’ve just described demonstrates the principle that CICS tuning isn’t just a matter of modifying CICS, regardless of the platform it runs on. Numerous IT components are involved, and it’s constantly evolving. Each generation of tuning builds on previous ones. Once tuning categories and constraints are delineated, a starting point for improved performance is established. Understanding CICS internals and tuning options, and detecting and revealing performance constraints are only the beginning. Performance monitoring and data collection will be the next article’s topic.

Jim Schesvold can be reached at

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