If a PDS is compressed after a checkpoint in which the PDS was open, restart at checkpoint should not be requested.

After you take a checkpoint and then open a PDS for adding or replacing members, another checkpoint should be taken before any records are written into the data set. If the second checkpoint is not taken and restart occurs at the first checkpoint, the OPEN routine positions to the current end of the data set instead of to the original end.

If a PDS is open for output (OPEN,OUTPUT) at the time of a checkpoint, then the restart function deletes any members added after the checkpoint. If the data set is open with the UPDAT, INOUT, or OUTIN option, then restart does not delete members unless another DCB is open for output to the data set. For example, the PDS is open for update, and the problem program is updating the third member of a five-member PDS, when checkpoint 1 is taken. If a member is updated as a newly rewritten member after checkpoint 1, and the program is restarted from that point, rewriting the updated member will cause problems because the member already exists.