Compressing the target libraries

You can use the COMPRESS operand of the APPLY command to have SMP/E compress the target libraries before installing SYSMODs. There are two methods of specifying which libraries are to be compressed:

You can specify a list of specific libraries in the COMPRESS operand (including libraries that may not be affected by the APPLY command).
You can specify ALL on the COMPRESS operand, in which case the only libraries eligible for compression are those in which elements will be installed by this APPLY command.

Note: Target libraries residing in a UNIX file system are not compressed.

Once the libraries have been determined, actual processing is dependent on the library type:

For source libraries, any source to be replaced (not updated) by one of the SYSMODs being installed is deleted from the library.
For macro libraries, no deleting is done. This is because the SYSMOD replacing the macro might fail, and there may be other SYSMODs that cause assemblies that use the macro.
For data element, hierarchical file system element, and program element libraries, any data element, hierarchical file system element, or program element that is to be replaced by one of the SYSMODs being installed is deleted from the library.
For load libraries, SMP/E determines which load modules within the library are composed only of modules copied during system generation and are being replaced by the SYSMODs being installed. Such load modules are deleted from the library. If a load module contains a module that is not being replaced, that load module is not deleted.

SMP/E then calls the copy utility to perform the actual compress operation.

Note:

To reclaim as much space as possible before installing the SYSMODs, members are deleted before the library is compressed. SMP/E processes one library at a time, first deleting members, then compressing the library.
When you install a function that deletes another function but supplies no elements, no libraries are compressed.