This is an extract from the online documenation.
Number of Database Backups configuration parameter - num_db_backups
12 [ 1 -- 32 768]
This parameter specifies the number of database backups to retain for a database. After the specified number of backups is reached, old backups are marked as expired in the recovery history file. Recovery history file entries for the table space backups and load copy backups that are related to the expired database backup are also marked as expired. When a backup is marked as expired, the physical backups can be removed from where they are stored (for example, disk, tape, TSM). The next database backup will prune the expired entries from the recovery history file.
Recovery History Retention Period configuration parameter - rec_his_retentn
366 [ -1; 0 -- 30 000 ]
Unit of Measure
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 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.
When a database backup is marked as expired in the history file, any corresponding file backups linked through a DB2 Data Links Manager will be removed from its archive server.
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