IMS Monitor

The IMS Monitor is a tool that records data about the performance of your DL/I databases in a batch environment.

The recorded data is produced in a variety of reports. The monitor's usefulness is twofold. First, when you run the monitor routinely, it gives you performance data over time. By comparing this data, you can determine whether the performance trend is acceptable. This helps you make decisions about tuning your database and determining when it needs to be reorganized.

The second use of the monitor is to assess how the changes you make effect performance. Once you have accumulated reports describing normal database processing, you can use them as a profile against which to compare the effect of your changes. Examples of changes you might make (then test for performance) include:
  • Changes in the structure of your databases
  • A change from one DL/I access method to another
  • A change in database buffer pool number and size
  • Changes in application program logic

In all these cases, your primary goal is probably to minimize the number of I/Os required to perform an operation. The monitor helps you determine whether you have met your objective.

The following example shows how to use the IMS Monitor: suppose you are performing a final test on a new or revised application. The monitor reports show that some DL/I calls in the program, which should have required a single I/O retrieval, actually required a large database scan involving many I/Os. You might be able to correct this problem by making changes in the application program logic.

The monitor itself is actually two programs, as shown in the following figure.
  • The IMS Monitor (DFSMNTR0)
  • The IMS Monitor Report Print utility (DFSUTR20)
Figure 1. How the IMS Monitor works
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The IMS Monitor collects data from IMS control blocks (when DL/I is operating) and records the data either on an independent data set or in the IMS log. It collects data with minimum interference to the system. The monitor runs in the same address space as the IMS job, and it can be turned on or off with the MON= parameter in the execution JCL.

The IMS Monitor Report Print utility is an offline program that produces reports summarizing information collected by the IMS Monitor. It produces the following reports:
  • VSAM Buffer Pool report
  • VSAM Statistics report
  • Database Buffer Pool report
  • Program I/O report
  • DL/I Call Summary report
  • Distribution Appendix report
  • Monitor Overhead report

Many of these reports are also provided by the IMS Monitor.

When the IMS Monitor is on, it remains on until the batch execution ends, requiring some overhead. It cannot be turned on and off from the system console. To minimize the monitor's impact, use the IMS Monitor in a single-thread test environment rather than multi-thread application environments.

This ensures that the data gathered by the IMS Monitor can be related to a particular program.