How IA affects performance

Running CICS® IA to obtain interdependency data and affinity data incurs a performance overhead. You must understand the cost of running the individual components of CICS IA and the performance overhead of running this workload in a single region CICS IA environment.

The environment that was used to take the measurements was configured as follows:

Performance data collection

The basic metrics for making a comparison between CICS with and without CICS IA data collection running were as follows: These metrics were all collected using RMF™.

Component testing

To determine the cost of individual components in CICS IA, basic COBOL programs were written. For example, to determine the cost of collecting interdependency data for file requests, a COBOL program was written that issued the following commands: The number of EXEC CICS READ commands to be issued was based on an input parameter from a simulated terminal device. Because each read is for the same record, this record exists in a VSAM buffer, and hence I/O activity is avoided.

A workload consisting of 500 simulated terminals is started using TPNS. RMF is then used to determine the CPU consumed per transaction.

Performance tests were run with both 50 and 100 EXEC CICS READ commands. The difference in the CPU time consumed per transaction in these two runs is solely associated with the 50 additional EXEC CICS READ commands. By dividing this difference by 50, the cost of a single EXEC CICS READ command can be determined.

By running these performance tests with the following CICS IA settings, the cost of an EXEC CICS READ in different environments can be compared:
  • CICS IA not running
  • CICS IA running with the Files field on the CICS Resources Option panel set to N.
  • CICS IA running with the Files field on the CICS Resources Option panel set to Y.
  • CICS IA running with the Files field on the CICS Resources Option panel set to D.

By comparing these four EXEC CICS READ costs, the CICS IA overhead for various Files=x settings can be determined.