CICS® performance analysis techniques

There are four main uses for performance analysis:

  1. You currently have no performance problems, but you simply want to adjust the system to give better performance.
  2. You want to characterize and calibrate individual stand-alone transactions as part of the documentation of those transactions, and for comparison with some future time when, perhaps, they start behaving differently.
  3. A system is departing from previously identified objectives, and you want to find out precisely where and why this is so. Although an online system may be operating efficiently when it is installed, the characteristics of the system usage may change and the system may not run so efficiently. This inefficiency can usually be corrected by adjusting various controls. At least some small adjustments usually have to be made to any new system as it goes live.
  4. A system may or may not have performance objectives, but it appears to be suffering severe performance problems.

This section discusses techniques you can use to analyze the performance of your system.

If the current performance does not meet your needs, you should consider tuning the system (see Tuning your CICS system). The basic rules of tuning are:

  1. Identify the major constraints in the system (see Identifying CICS constraints).
  2. Understand what changes could reduce the constraints, possibly at the expense of other resources. (Tuning is usually a trade-off of one resource for another -- see Determining acceptable tuning trade-offs.)
  3. Decide which resources could be used more heavily.
  4. Adjust the parameters to relieve the constrained resources (see Making tuning changes to your system).
  5. Review the performance of the resulting system in the light of: See Virtual telecommunication access method (VTAM) trace.
  6. Stop if performance is acceptable; otherwise do one of the following:

The tuning rules can be expressed in flowchart form as follows:

Figure 52. Flowchart to show rules for tuning performance
 First, understand the performance objectives. Second, monitor the system following a measurement and evaluation plan, to establish objectives, resource contention, and predictions. Third, check whether the performance objectives are currently being met. If the performance objectives are currently being met, continue to monitor the system following your plan. If the performance objectives are not currently being met, take the following steps. Identify a major resolvable resource contention. Devise a tuning strategy that will minimize usage of resource and/or expand the capacity of the system. Identify the variables. Predict the effects. Make the change. Now re-check whether the performance objectives are currently being met, and repeat these steps again as necessary, until they are being met.

This section discusses techniques for performance analysis in the following sections:

Related tasks
Identifying CICS constraints
Tuning your CICS system
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