GDG files

ABENDed application programs can usually be restarted through QUICKSTART without any temporary JCL changes. The only instances where JCL changes are necessary are those where the application program creates new Generation Levels of a Generation Dataset Group (“GDG”). This includes any datasets where the dataset name subparameter specifies DSN=...(+1).

If the JCL specifies a Generation Level of other than (+0), (e.g. (+1)), the Generation Level argument of the JCL must be altered during a restart in order to access the proper Generation Level. If the Step had only (+1) references, they must be changed to (+0). However, if the Step had references of (+1) and (+2), then those must be changed to (-1) and (+0), respectively.

JCL changes for successful restart for GDGs are not necessary if either of the following two methods are adapted:

• A preceding job can “pre-allocate” the GDG as (+1). The job containing the application program can then contain references to the GDG as (+0) on a new run or a restart.
• Instead of writing to a GDG, the JCL should specify a normal sequential dataset. A subsequent job step can then copy the sequential dataset to the GDG as (+1).

By making either adjustment to the JCL, there should be no need for temporary JCL modifications in order to restart the application program.