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Rollback and recovery (RR) is a method of enchancing the reliability of file or data base systems. At certain points in time, called checkpoints, a copy of the data or files is made on tape (or other storage devices). A chronological record is kept of all transactions which modify the data stored by the system; this record is called the audit trail. When an error is detected, the copy of the files or data made at the most recent checkpoint is loaded, and all transactions on the audit trail since this check point are reprocessed in chronological sequence, thus recovering from the error. This paper presents models and techniques which aid in determining optimal times for checkpoints.