"Translated from MoS article" Why does Rman not use the unused block compression function during the backup process

Why is Rman not using the unused block compression feature during the backup process?
From:
Why is the RMAN not using Unused Block Compression during backup? (Document ID 798844.1)

Suitable for:
Oracle database-enterprise edition-version 10.2.0.1 to 11.2.0.2 [Release 10.2 to 11.2]
Information in this document applies to any platform.
Checked for relevance on 27-nov-2013***

Goal:
In the case of version 10.2, and all of the following conditions are met, Rman will use the unused block compression feature:

The COMPATIBLE initialization parameter is set to 10.2There be currently no guaranteed restore points defined for the DAT Abasethe datafile is locally managedthe datafile are being backed up to a backup set as part of a full backup or a level 0 Incremental Backupthe backup set is being created on disk or  OSB backup to tape

note:http://download.oracle.com/docs/cd/e11882_01/backup.112/e10643/rcmsynta007.htm#i1015382. Oracle Database Backup and Recovery reference11g Release 2 (11.2) part number e10643-04. Backup    backuptypespecnote:if COMPATIBLE is set to 10.2 and then only tablespaces created with 10.2 compatibility would be Optimized to exclude blocks this does not currently contain data.  If COMPATIBLE is set to 11.0.0 or higher, however and then the first backup, this produces backup sets after COMPATIBLE is set  To 11.0.0 or higher would update the headers of all locally managed datafiles so, all locally managed datafiles can be Optimized.

However, the following query from V$backup_datafile shows that all datafile are scanned during the backup (%read is 100)

sql> Set lines 120sql> select file# fno, used_change_tracking BCT,            incremental_level INCR, Datafile_blocks blks ,            block_size Blksz, Blocks_read read,            round ((blocks_read/datafile_blocks) * 100,2) "%read",            blocks Wrtn, Round ((blocks/datafile_blocks) *100,2) "%wrtn" from       v$backup_datafile      where completion_time between            to_ Date (' 25-jan-09 01:30:00 ', ' dd-mon-rr hh24:mi:ss ') and            to_date (' 26-jan-09 12:35:26 ', ' dd-mon-rr hh24:mi:ss ')   Order by file#;----change the dates as necessary to encompass the backup start and end times--and check the%read value For each datafile.----> modifies the WHERE condition of the above script to serve as a common script for querying the datafile scan rate.

Solution:
Unused block compression is not applicable for version 10.2.0.1.
Unused block compression can only be used if the tablespace established after hitting 10.2.0.2patch

Therefore, you cannot use the unused block compression feature for table spaces such as the following:
Table space created before 10.2.0.2
Table space created before compatible is set to 10.2

The cause of this problem have been identified and verified in a ' unpublished ' Bug 4720762-fixed in Product Version 11.0

"Translated from MoS article" Why does Rman not use the unused block compression function during the backup process