There are four main uses for performance analysis:
- You currently have no performance problems, but you simply want to adjust
the system to give better performance.
- 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.
- 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.
- 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:
- Identify the major constraints in the system (see Identifying CICS constraints).
- 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.)
- Decide which resources could be used more heavily.
- Adjust the parameters to relieve the constrained resources (see Making tuning changes to your system).
- Review the performance of the resulting system in the light of:
- Your existing performance objectives
- Progress so far
- Tuning effort so far.
See Virtual telecommunication access method (VTAM) trace.
- Stop if performance is acceptable; otherwise do one of the following:
- Continue tuning
- Add suitable hardware capacity
- Lower your system performance objectives.
The tuning rules can be expressed in flowchart form as follows:
This section discusses techniques for performance analysis in the following
sections:
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