The choice of macro determines the linkage relationship between the calling program and the sort/merge load module. The linkage relationship established by ATTACH precludes the use of the Checkpoint-Restart feature; do not code CHKPT/CKPT on the SORT/MERGE control statement when invoking the sort/merge with the ATTACH macro. With XCTL, care must be taken to ensure that the storage area for the parameter list and other sort control information does not reside in the module issuing the macro - XCTL will delete this module from memory. This problem can be circumvented in two ways. Either (1) place the parameter list and additional control information in the task that attaches the module issuing the XCTL; or (2) have the module issuing the XCTL macro issue a GETMAIN macro instruction first, and place all of the sort/merge control information in the main storage area it obtains. None of the above restrictions apply when using the LINK macro.
The sort/merge DD statements are placed with the JCL of the job step that issues the macro. The EP parameter is specified as SORT whether MFX is to be used for sorting, merging, or copying. With ATTACH, the ECB or EXTR is usually required.