RMAN Recovery Window retention policy tips

Question: I need to understand the concept of RMAN retention policy settings and the idea of a retention policy for a specific recovery windows. How does the recovery window relate to the retention policy?

Answer (by Aman Sharma): The Recovery Window retention policy doesn't just keep the last N days of the backup. It calculates the point-of-recovery (POR) value, accounting the current date and the number of the days mentioned in the retention policy.

The POR is more than just the backup of the last N days. In addition, you would also need the backup of all those which come under the calculation of POR. For example, assume today is 20th of April (we shall not count year here since it’s not needed) and you decide to go with the Recovery Window of 2 days.

In the case of non-incremental backup, this is how it would look:

Current_Date        Status         POR           
20-April           Available       20-2=18th April
21-April           Available       21-2= 19th April
22-April           Available       22-2=20th April
23-April  Backup of 20th Obsoleted 23-2=21st April

So in the case of 23rd, the backup would be marked as obsolete.

The same would be true in the case of the incremental backup as well with one additional layer that now, instead of just one backup, oracle would consider this also that whether the backup is a level 0 or level 1 backup and won't consider the backup of level 1 obsolete if it’s still needed for the recovery.

For complete details, see my book Oracle Backup & Recovery: Expert secrets for using RMAN.

Get the Complete Oracle Backup & Recovery Details  The landmark book "Oracle Backup & Recovery: Expert secrets for using RMAN and Data Pump " provides real world advice for resolving the most difficult Oracle performance and recovery issues. Buy it for 40% off directly from the publisher.

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