(ZOS) Tune for applications that access CICS in z/OS

If the application accesses CICS, we might in some cases want to consider tuning the log defer interval value.

This information applies only to WebSphere applications that access CICS .

The LGDFINT system initialization parameter specifies the log defer interval used by CICS log manager when determining how long to delay a forced journal write request before invoking the MVS™ system logger. The value is specified in milliseconds.

Performance evaluations of typical CICS transaction workloads have shown that the default setting of 5 milliseconds gives the best balance between response time and central processor cost. Be aware that CICS performance can be adversely affected by a change to the log defer interval value. Too high a value delays CICS transaction throughput due to the additional wait before invoking the MVS system logger.

An example of a scenario where a reduction in the log defer interval might be beneficial to CICS transaction throughout is where many forced log writes are being issued, and little concurrent task activity is occurring. Such tasks spend considerable amounts of their elapsed time waiting for the log defer period to expire. In such a situation, there is limited advantage in delaying a call to the MVS system logger to write out a log buffer, because few other log records are added to the buffer during the delay period.

For more detailed information on CICS, refer to the CICS Performance Guide.

Tasks

1. Set the LGDFINT system initialization parameter to 5 While CICS is running, we can use the CEMT SET SYSTEM[LOGDEFER(value)] command to alter the LGDFINT setting dynamically.

2. Set the CICS RECEIVECOUNT value high enough to handle all concurrent EXCI pipes on the system. The default is 4. You set this value in the EXCI sessions resource definition.

Tuning parameter hot list