Oracle11g 新特性：优化Rman备份UNDO表空间

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Oracle11gR1的新特性，Rman备份UNDO表空间时排除已经提交的会话对应的数据，提高了Rman备份的效率。

官方文档：http://docs.oracle.com/cd/B28359 ... er1.htm#AREANO02323
我们知道，UNDO表空间主要用于存储前镜像数据，这些数据在回滚以及恢复过程中可能被用到。但是一个生产数据库的UNDO表空间可能会变得非常巨大，而备份完整的UNDO数据文件在恢复时一般可能用到的比例很小。
测试一下：

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--数据库版本 sys@ORCL>select * from v$version; BANNER ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production PL/SQL Release 11.2.0.4.0 - Production CORE    11.2.0.4.0  Production TNS for Linux: Version 11.2.0.4.0 - Production NLSRTL Version 11.2.0.4.0 - Production --创建环境 zx@ORCL>insert into t1 select * from dba_segments; 5887 rows created. zx@ORCL>insert into t1 select * from dba_segments; 5887 rows created. zx@ORCL>insert into t1 select * from dba_segments; 5887 rows created. zx@ORCL>insert into t1 select * from dba_segments; 5887 rows created. zx@ORCL>insert into t1 select * from dba_segments; 5887 rows created. zx@ORCL>insert into t1 select * from dba_segments; 5887 rows created. zx@ORCL>insert into t1 select * from dba_segments; 5887 rows created. zx@ORCL>insert into t1 select * from dba_segments; 5887 rows created. zx@ORCL>insert into t1 select * from dba_segments; 5887 rows created. zx@ORCL>commit; Commit complete. zx@ORCL>delete from t1; 288463 rows deleted. zx@ORCL>select status,sum(bytes)/1024/1024 from dba_undo_extents group by status; STATUS              SUM(BYTES)/1024/1024 --------------------------- -------------------- UNEXPIRED                  9.125 EXPIRED                   .4375 ACTIVE                    89.125 zx@ORCL>commit; Commit complete. --两次备份undo表空间文件 RMAN> backup datafile 5; Starting backup at 2016-12-22 13:09:27 using channel ORA_DISK_1 channel ORA_DISK_1: starting full datafile backup set channel ORA_DISK_1: specifying datafile(s) in backup set input datafile file number=00005 name=/u02/app/oracle/oradata/orcl/undotbs2_01.dbf channel ORA_DISK_1: starting piece 1 at 2016-12-22 13:09:27 channel ORA_DISK_1: finished piece 1 at 2016-12-22 13:09:28 piece handle=/u02/app/oracle/product/11.2.4/db1/dbs/3aro4007_1_1 tag=TAG20161222T130927 comment=NONE channel ORA_DISK_1: backup set complete, elapsed time: 00:00:01 Finished backup at 2016-12-22 13:09:28 Starting Control File and SPFILE Autobackup at 2016-12-22 13:09:28 piece handle=/u02/app/oracle/product/11.2.4/db1/dbs/c-1444351641-20161222-0f comment=NONE Finished Control File and SPFILE Autobackup at 2016-12-22 13:09:31 --查看备份后的文件大小 RMAN> list backup of datafile 5; List of Backup Sets =================== --第一次备份文件大小99.27M BS Key  Type LV Size       Device Type Elapsed Time Completion Time    ------- ---- -- ---------- ----------- ------------ ------------------- 87      Full    99.27M     DISK        00:00:03     2016-12-22 12:11:54         BP Key: 87   Status: AVAILABLE  Compressed: NO  Tag: TAG20161222T121151         Piece Name: /u02/app/oracle/product/11.2.4/db1/dbs/36ro3sk7_1_1   List of Datafiles in backup set 87   File LV Type Ckp SCN    Ckp Time            Name   ---- -- ---- ---------- ------------------- ----   5       Full 9042031    2016-12-22 12:11:51 /u02/app/oracle/oradata/orcl/undotbs2_01.dbf --第二次备份文件大小2.16M BS Key  Type LV Size       Device Type Elapsed Time Completion Time    ------- ---- -- ---------- ----------- ------------ ------------------- 89      Full    2.16M      DISK        00:00:01     2016-12-22 12:34:42         BP Key: 89   Status: AVAILABLE  Compressed: NO  Tag: TAG20161222T123441         Piece Name: /u02/app/oracle/product/11.2.4/db1/dbs/38ro3tv1_1_1   List of Datafiles in backup set 89   File LV Type Ckp SCN    Ckp Time            Name   ---- -- ---- ---------- ------------------- ----   5       Full 9042576    2016-12-22 12:34:41 /u02/app/oracle/oradata/orcl/undotbs2_01.dbf --查看操作系统文件大小 [oracle@rhel6 release]$ ls -lh /u02/app/oracle/product/11.2.4/db1/dbs/36ro3sk7_1_1 -rw-r----- 1 oracle oinstall 100M Dec 22 12:11 /u02/app/oracle/product/11.2.4/db1/dbs/36ro3sk7_1_1 [oracle@rhel6 release]$ ls -lh /u02/app/oracle/product/11.2.4/db1/dbs/38ro3tv1_1_1 -rw-r----- 1 oracle oinstall 2.2M Dec 22 12:34 /u02/app/oracle/product/11.2.4/db1/dbs/38ro3tv1_1_1

这个新特性也有一些限制
- Compatible parameter must be set to 11.0 or higher
- Backup must use a disk or OSB channel
- For 'backup copy of <object>' or 'backup datafilecopy' the database must be open for undo optimization to be used.
- Not active for LEVEL 1 incremental backups, only for LEVEL 0 and FULL backups
MOS文档：RMAN 11G : RMAN UNDO backup optimization (文档 ID 406468.1)
A Complete Understanding of RMAN Compression (文档 ID 563427.1)