This parameter is used to specify the number of days that historical information on backups should be retained. If the recovery history file is not needed to keep track of backups, restores, and loads, this parameter can be set to a small number.
If value of this parameter is -1, the recovery history file can only be pruned explicitly using the available commands or APIs. If the value is not -1, the recovery history file is pruned after every full database backup.
The value of this parameter will override the value of the num_db_backups parameter, but rec_his_retentn and num_db_backups must work together. If the value for num_db_backups is large, the value for rec_his_retentn should be large enough to support that number of backups.
No matter how small the retention period, the most recent full database backup plus its restore set will always be kept, unless you use the PRUNE utility with the FORCE option. For more information about this utility, refer to the Command Reference.