【mos記事から翻訳】なぜバックアップ中にrmanがunused block圧縮機能を使用しないのか

なぜバックアップ中にrmanがunused block圧縮機能を使用しないのですか?出典:Why is RMAN not using Unused Block Compression during backup?(文書ID 798844.1)
適用: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***
ターゲット:10.2バージョンで、次のすべての条件を満たす場合、rmanはunused block圧縮機能を使用します.

The COMPATIBLE initialization parameter is set to 10.2
There are currently no guaranteed restore points defined for the database
The datafile is locally managed
The datafile is being backed up to a backup set as part of a full backup or a level 0 incremental backup
The 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 Reference
11g Release 2 (11.2)
Part Number E10643-04
.
Backup
    backupTypeSpec

Note:
If COMPATIBLE is set to 10.2, then only tablespaces created with 10.2 compatibility will be optimized to exclude blocks that do not currently contain data. If COMPATIBLE is set to 11.0.0 or higher, however, then the first backup that produces backup sets after COMPATIBLE is set to 11.0.0 or higher will update the headers of all locally managed datafiles so that all locally managed datafiles can be optimized.

 
ただし、以下はv$backup_からDatafileのクエリーによると、バックアップ中にすべてのdatafileがすべてスキャンされた(%READは100)

SQL> set lines 120
SQL> 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.
--
--> where ， datafile  。

 
ソリューション:unused block圧縮は10.2.0.1バージョンでは適用されません.unused block圧縮は、10.2.0.2 patchの後に確立されたtablespaceでのみ使用できます.
したがって、10.2.0.2以前に確立されたテーブル空間がcompatibleが10.2に設定される前に確立されたテーブル空間はunused block圧縮機能を使用できない
 
The cause of this problem has been identified and verified in an 'unpublished' Bug 4720762 - Fixed in Product Version 11.0