Application Trace Facility (ATF) is an important DevOps tool across the IMS environment. Available through OMEGAMON for IMS 5.5, it enables tracing of DL/I calls as well as ESAF API calls such as DB2 SQL and MQ. It provides summary and detail metrics for determining the performance of transactions. As a result, it is very useful in debugging performance issues across the lifecycle of an IMS application.
Application tracing has a cost though, especially with detail trace. If it is always on, the overhead of tracing can impact the throughput of your system. So, management of ATF is important. Using filters, exceptions, and summarization are primary techniques for reducing the overhead of ATF.
By managing the performance of ATF, you can reap the benefits. Through tracing, you can quickly and easily debug application logic. The trace results may surprise you with its details! ATF enables you to troubleshoot performance problems. It can capture diagnostic information for abnormally behaving transactions. And its results can be leveraged by other products. For example, the captured data can be leveraged offline for use with IMS Performance Analyzer to gain additional insight. It can also be leveraged for enterprise accounting and determining charge backs for transaction processing. You can learn more about ATF here: https://www.ibm.com/docs/en/om-ims/5.5.0?topic=reference-application-trace-facility-overview
With all this functionality and these capabilities, it is critical that the footprint or CPU utilization by ATF itself remains as small as possible. That’s why the introduction of the new FASTMON exit type within IMS is incredibly important and should be considered for migration from IMSMON as soon as possible for ATF users. IMSMON, being a Type-2 IMS exit, is refreshable but has a higher overhead in the IMS framework supporting the REFRESH functionality. ATF, as an IMSMON exit exploiter, suffers with that overhead.
With PTF UI76510, IMS introduced a Type-1 exit, FASTMON, that is fast but not refreshable and requires an IMS restart to pick up changes. When used with the corresponding OMEGAMON PTF UJ06252, the Application Trace Facility has shown that it can reduce its overhead by double digit percentage points in a variety of lab measurements. Your experience may vary, but deploying the FASTMON capability with ATF should result in significant CPU reduction compared to IMSMON.
It is very easy to make the change and exploit this capability. Within the DFSDFxxx member in your IMS PROCLIB, simply change IMSMON to FASTMON on EXITDEF entry, while also changing the exit program name that was originally KOIMON00 to KOIMONF0. As both APARs require an IMS recycle, apply them during the same IMS maintenance window to minimize down time.
Additional information can be found in the technote: https://www.ibm.com/support/pages/node/6478103. I also presented this topic at the IBM OMEGAMON Technical Summit on September 22nd. There we covered several other topics including the latest on Configuration Manager, OMEGAMON for CICS and JVM. You can register here and get access to the event recording.
If you haven’t considered ATF within your environment today, there’s no excuse now with its improved performance. If you are using ATF today, switch to FASTMON and enjoy the CPU savings immediately.
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