I guess you're talking about cobol programms having EXEC SQL statements and the compiler option DYNAM/NODYNAM.
When you run under:
TSO or IMS: You can use either the DYNAM or NODYNAM compiler option.
Note that IMS and DB2 share a common alias name, DSNHLI, for the language interface module. You must concatenate your libraries as follows: If you use IMS with the DYNAM option, concatenate the IMS library first. If you run your application only under DB2, concatenate the DB2 library first. CICS or the DB2 call attach facility (CAF): You must use the NODYNAM compiler option. Because stored procedures use CAF, you must also compile COBOL stored procedures with the NODYNAM option.
A program compiled as RENT is generated as a reentrant object program. A program compiled as NORENT is generated as a nonreentrant object program. Either can be invoked as a main program or subprogram.
DATA and RMODE settings: The RENT option interacts with other compiler options that affect storage and its addressability. When a reentrant program is to be run with extended addressing, you can use the DATA(24|31) option to control whether dynamic data areas are allocated in unrestricted storage or in storage obtained from below 16 MB. Compile programs with RENT or RMODE(ANY) if they will be run with extended addressing in virtual storage addresses above 16 MB.
RENT also affects the RMODE (residency mode) of your generated object program. All Enterprise COBOL programs are AMODE ANY.
DATA: The setting of the DATA option does not affect programs compiled with NORENT.
CICS: You must use RENT for programs to be run under CICS.
UNIX: You must use RENT for programs to be run in the UNIX environment.
DB2: RENT is recommended for DB2 stored procedures, especially programs designated as main.