The AMP Parameter

The AMP parameter has a subparameter for specifying checkpoint/restart options that handle two special situations in restarting a processing program:

Modifications to the data set other than records added sequentially to the end of an entry-sequenced data set. The restart program cannot restore a data set to its checkpoint status if there have been internal modifications to it since the checkpoint, so the restart program does not attempt restart processing.
Addition of records to the end of a data set by way of a job step other than the job step that issued the checkpoint. Any records added to the end of an entry-sequenced data set are erased in restoring the data set to its checkpoint status.

The AMP options for checkpoint/restart are:

Let restart take its normal action for both situations
Override either one or the other of the two actions
Override both actions.

If you override the check for internal modification, the processing program is restarted, even though the data set being processed cannot be restored. If you override erasing data at the end of a data set and the catalog has been updated, the processing program is not restarted unless you also override the check for modification. For more detail on multiple ACBs open against the same data set, see z/OS DFSMS Macro Instructions for Data Sets.

To prevent data from being erased or to allow restart with modified data sets, the CROPS subparameter of the AMP parameter must be coded in the DD statement for the cluster or data set.

When more than one ACB is opened for output for the same data set using DDN sharing and the same DD statement, or using DSN sharing, the first ACB to be opened will establish the CROPS parameter for the data set. If this is not done, the results are unpredictable.

Repositioning is mandatory for all VSAM data sets open for create mode processing, except for relative record data sets processed in direct mode. If AMP=‘CROPS=NRE’ or AMP=‘CROPS=NRC’, no checkpoint is taken. If a checkpoint is attempted, message IHJ000I is issued, and a return code of X'08' is returned in register 15. A reason code of 41 in register 0 is also returned to you.

If a VSAM data set supported for repositioning extends to a new volume after the checkpoint, VSAM restart cannot reposition the data set. A restart from that checkpoint is not successful unless the no-reposition option is taken by specifying AMP=‘CROPS=NRE’ or AMP=‘CROPS=NRC’.