How CA PMO Optimizes Directory Searches › Searches Initiated by Program Management

Searches Initiated by Program Management

Program Management is a component of z/OS that finds load modules needed by a program or application, and loads the modules into virtual storage (unless they are already there). Program Management also links, attaches, and transfers control to the load module. Program Management uses a standard order of search for a load module:

1. Job Pack Area (JPA) — This is an area in the virtual address space of a job that contains load modules. A search of the JPA is an in-storage search of all modules that were previously loaded by an application or program.
2. JOB/STEP/TASK Libraries — This is a DASD I/O search of the directories of the private JOB/STEP/TASK libraries that were specified in the JCL. (These searches may be replaced by an in-storage LLA search, if LLA is managing these libraries.)
3. Link Pack Area (LPA) — The LPA is a virtual storage area that contains reentrant load modules. Reentrant load modules are loaded at IPL time. They can be used concurrently by all tasks on the system. An LPA search is an in-storage search of the reentrant system load modules.
4. LNKLST Libraries, Library Lookaside (LLA) — This is a search of LNKLST library directories. The in-storage LLA address space can resolve all LNKLST library directory searches. Others may require DASD I/O.

The following illustration shows the Program Management standard order of search. Note that in step 2 of this flowchart, the DASD search may be replaced by an in-storage LLA search. This is the case if the JOB/STEP/TASK libraries are managed by LLA.

Program management follows a standard order of search to locate a program load module. Up to two DASD directory searches might be initiated, one in step 2 and one in step 4. The DASD search in step 2 may be replaced by an in-storage search of LLA.

Program Management Standard Order of Search

If Program Management finds the module, it reads the module into virtual storage, unless it is already there. (If LLA manages the library that contains the module, Program Management may obtain the module from the VLF data space. The VLF data space contains frequently requested load modules.) If Program Management does not find the module, it issues an S806 abend for the program or application that invoked the module.