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:
- An LPAR with three dedicated CPUs on an IBM® 2084-303 mainframe system
- IBM ESS 800 Enterprise Storage Server®
- z/OS® V1.9
- CICS TS V3.2
- CICS IA V2.2.0
- DB2® V7.1
- WebSphere® MQ V6.0
Performance data collection
The basic metrics
for making a comparison between CICS with
and without CICS IA data collection
running were as follows:
- Transaction rate (ETR)
- CICS region CPU usage
- CICS internal response
times
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:
- EXEC CICS RECEIVE
- A variable number of EXEC CICS READ
commands for the same VSAM record
- EXEC CICS SEND
- EXEC CICS RETURN
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.