Before you install modules in the MVS link pack area, you should consider the following points, described in subsequent topics:
The benefits of placing code in the MVS link pack area are:
If you know the amount of space that you need in the LPA, and from that the total size of the MVS™ common area above the CICS private storage, you can determine which 1MB segment the boundary between the two areas lies on. This may indicate that there is some space in the MVS common area that is left unused, which you could use for CICS LPA-eligible modules. By moving more modules from CICS private storage to the LPA, you decrease the space that is needed for modules in CICS private storage.
The MVS link pack area comprises several areas, both above and below 16 MB. In this publication, the term MVS link pack area refers to the pageable link pack areas above and below 16MB where modules that are used from the MVS link pack area are normally installed.
The term LPA specifically refers to the MVS link pack area below 16 MB, and the term ELPA specifically refers to the area above 16MB. A module that is link-edited with the RMODE(ANY) attribute is loaded into the ELPA.
If you install a module into the LPA or ELPA,
that module will not be retrieved from the until you re-IPL
your MVS with CLPA specified. To use the new module
and avoid an IPL, you can use the MVS dynamic LPA in one of the following
ways:
Note that dynamic LPA must not be used with DFHIRP.
The CICS modules listed in Table 10 must be in the MVS link pack area for the reasons that are given in the notes after the table.
Module | Description | When needed in LPA | See notes after this table |
---|---|---|---|
DFHCSVC | CICS Type 3 SVC | Always | 1, 2, 3,4, and 6 |
DFHDSPEX | CICS post exit stub | Always | 1 , 3, and 5 |
DFHDUMPX | SDUMPX IEASDUMP QUERY exit | Always | 1, and 3 |
DFHIRP | Interregion communication program | To use MRO, CICS shared database, or the console message-handling facility | 1, 2, 3, and 6 |
DFHSSEN | Subsystem interface end-of-memory / end-of-task clean up routine | To use the console message-handling facility | 1, 2, 3, and 6 |
DFHSSGC | Subsystem generic connect module | To use the console message-handling facility | 3, and 7 |
DFHSSWT | Subsystem interface WTO router | To use the console message-handling facility | 3, and 7 |
DFH99SVC | Dynamic allocation - SVC services | Always | 1, and 3 |
Do not use the linkage editor to install the CICS SVC module into a library in the MVS link pack area. To copy or move the module from the hlq.SDFHAUTH library to the nominated library in the MVS link pack area, you should use either a suitable copy utility program, such as IEBCOPY, or an SMP/E USERMOD with ++MOVE statements.
If a region detects that DFHIRP is at a lower level, when attempting to open interregion communication, it issues message DFHIR3799, and interregion communication fails to open.
Besides those CICS modules that must be in the MVS link pack area, other CICS modules and user application program modules are available from the MVS link pack area.
A CICS module optionally installed in the MVS link pack area (that is, not a module required in the MVS link pack area) can be used only by the release of CICS to which it relates.
Those CICS modules that can reside above 16MB (for example, the CICS message table, DFHMGT), are loaded above 16MB. Such modules can also be installed in the extended link pack area (ELPA).
CICS modules eligible to be used from the MVS link pack area are listed in the CICS-supplied USERMODs, DFH$UMOD (for base CICS modules), which is in the hlq.SDFHSAMP library. Details of LPA-eligible modules are in Appendix. CICS modules eligible for the MVS link pack area, to help you select those CICS modules that you want to install in the MVS link pack area.
User application programs can be used from the MVS link pack area if they are read-only and:
Command-level user application programs compiled using a Language Environment-conforming compiler, or written in Assembler language or C/370, may be loaded above 16MB. (For information about installing application programs, see the CICS Application Programming Guide.)
A read-only module that may reside above 16MB is also eligible for the extended link pack area (ELPA).
Using modules with mismatching service levels can cause unpredictable results. To be safe, do not use the LPA version of a module if it differs from the version in the CICS libraries that you are using.
Load modules used from the LPA might be at a lower service level than the rest of your CICS region in any of the following circumstances:
Thus, if you have applied service to a load module in your CICS libraries, you should also apply the service to the LPA version of the module, if one exists. This stipulation is there so that the MVS link pack area always contains tested load modules.
Use the SMP/E RESTORE function to back off the USERMOD before the LPA zone is updated or copied. Then apply the USERMOD again.
If you have used a copy of the CICS-supplied USERMODs to install modules into the MVS link pack area, and the original USERMOD is serviced, you may like to reflect the changes in your version of the USERMOD.
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