Oracle11g 新特性：优化Rman备份UNDO表空间

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_01/server.111/b28279/chapter1.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：

--数据库版本sys@ORCL>select * from v$version;BANNER------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit ProductionPL/SQL Release 11.2.0.4.0 - ProductionCORE    11.2.0.4.0      ProductionTNS for Linux: Version 11.2.0.4.0 - ProductionNLSRTL 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                                  9.125EXPIRED                               .4375ACTIVE                                    89.125zx@ORCL>commit;Commit complete.--两次备份undo表空间文件RMAN> backup datafile 5;Starting backup at 2016-12-22 13:09:27using channel ORA_DISK_1channel ORA_DISK_1: starting full datafile backup setchannel ORA_DISK_1: specifying datafile(s) in backup setinput datafile file number=00005 name=/u02/app/oracle/oradata/orcl/undotbs2_01.dbfchannel ORA_DISK_1: starting piece 1 at 2016-12-22 13:09:27channel ORA_DISK_1: finished piece 1 at 2016-12-22 13:09:28piece handle=/u02/app/oracle/product/11.2.4/db1/dbs/3aro4007_1_1 tag=TAG20161222T130927 comment=NONEchannel ORA_DISK_1: backup set complete, elapsed time: 00:00:01Finished backup at 2016-12-22 13:09:28Starting Control File and SPFILE Autobackup at 2016-12-22 13:09:28piece handle=/u02/app/oracle/product/11.2.4/db1/dbs/c-1444351641-20161222-0f comment=NONEFinished 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99.27MBS 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2.16MBS 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