Program load and initialization

Dynamic and daily monitoring

The resource used to load or initialize a program cannot be isolated or corrected dynamically from normal daily monitoring data. Usually, this aspect of performance, once it is tuned, does not require more than periodic monitoring.

The IMS.PGMLIB data set is specified in the dependent region JCL and contains the application programs. The schedule-to-first DL/I call elapsed time shown on the IMS Monitor Region Summary and Program Summary reports includes the I/O time to bring a program into the region. Included in the I/O time is the system search through JOBLIB (searched first) or STEPLIB. If JOBLIB and STEPLIB are not used for the program library, IMS.PGMLIB should be first in the LNKLSTnn member of SYS1.PARMLIB. Program libraries should always be blocked to full track size. Placement in the dependent region STEPLIB is recommended because a library can be built containing only those members required by the region.

In environments that are not constrained by real storage availability, consider making a trade-off between program loading and preload. You can use the schedule-to-first DL/I call elapsed times from the IMS Monitor Region Summary report to assess the potential savings of preload.

z/OS® Library Lookaside (LLA) is the strategic method for managing dynamically loaded program libraries.

Related reading: For more information on LLA, see Using Library Lookaside under z/OS.

Detailed monitoring

The GTFPARS Job Summary and Detail Trace reports for the IMS Message Regions can provide comprehensive data on the counts and sequences of SVC and I/O operations issued to locate and load the user's application program, and to execute the high-level language initialization modules.

For information about program library options and initialization considerations, see Choosing IMS options for performance.