For best performance in the IMS environment, use the RENT compiler option. It causes COBOL to generate reentrant code. You can then run your application programs in either preloaded mode (the programs are always in storage) or nonpreload mode, without having to recompile with different options.
IMS allows COBOL programs to be preloaded. This preloading can boost performance because subsequent requests for the program can be handled faster when the program is already in storage (rather than being fetched from a library each time it is needed).
You must use the RENT compiler option to compile a program that is to be run preloaded or as both preloaded and nonpreloaded. When you preload a load module that contains COBOL programs, all of the COBOL programs in that load module must be compiled with the RENT option.
| Enterprise COBOL | IBM COBOL | VS COBOL II | OS/VS COBOL |
|---|---|---|---|
| RENT | RENT | RENT and RES | RES and NOENDJOB for preloaded
programs RES and ENDJOB for nonpreloaded programs |
You can place programs compiled with the RENT option in the LPA or ELPA. There they can be shared among the IMS dependent regions.
To run above the 16-MB line, your application program must be compiled with either RENT or NORENT RMODE(ANY), depending on your IMS environment.
With IMS, the data for IMS application programs can reside above the 16-MB line, and you can use DATA(31) RENT, or RMODE(ANY) NORENT for programs that use IMS services.