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From ORACLE-BASE:

CONFIGURE RETENTION POLICY TO RECOVERY WINDOW OF 7 DAYS;
CONFIGURE RETENTION POLICY TO REDUNDANCY 5;

The recovery window is used to make sure that there are always sufficient backups to recover the database to any point in time with the last 'X' days. Any backups that fall outside this time period can be deleted. The redundancy option simply states that any backups in excess of the latest 'X' are no longer needed.

In other words, setting the RMAN retention policy to a recovery window explicitly guarantees PITR to any time within the recovery window. It isn't clear from this description whether PITR is guaranteed using the alternative redundancy configuration — does RMAN retain all archivelog backups necessary for PITR to any point since the earliest retained backup?

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Does RMAN retain all archivelog backups necessary for PITR to any point since the earliest retained backup?

No, at least not if you have incremental backups in the mix:

…we don’t guarantee a recoverability to a certain point in time, just, the number of backupsets.

I'm not sure if the same applies if you aren't using incrementals, but there are too many edge cases with using a redundancy-based policy (see this horror story for example). Use a recovery window instead if you possibly can. The article you quote has the same advice:

The safest option is to use the redundancy window as several backups on a single day could cause the redundancy option to mark valuable files as redundant.

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  • I think it would be safe to say that redundancy based will guarantee PITR to any point in time since the oldest redundant backup. The problem comes in that there is no guarantee of what time frame that covers. Today it might be 3 weeks. Then over the next 24-hours you take several full or incremental backups and as a result, the oldest is just 24 hours old. As @Jack Douglas said, safest to just forget about redundancy and use recovery window.
    – EdStevens
    Mar 15 '17 at 22:35
  • "I think it would be safe to say that redundancy based will guarantee PITR to any point in time since the oldest redundant backup." It does not — did you check the link? I investigated this because a PITR restore failed reporting a missing archivelog backup when I expected it to be there. Mar 15 '17 at 22:50

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