Oracle11g新增了对于UNDO表空间的优化功能，对于UNDO表空间中的内容，对于恢复没有帮助的数据，Oracle不会备份。也就是说，Oracle不备份已经提交的数据。
首先对比一下10g和11g的情况：
$ sqlplus "/ as sysdba"
SQL*Plus: Release 10.2.0.3.0 - Production on 星期六 9月 22 23:36:04 2007
Copyright (c) 1982, 2006, Oracle. All Rights Reserved.
连接到:
Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 - 64bit Production
With the Partitioning, Real Application Clusters, OLAP and Data Mining options
SQL> select
2 (select sum(bytes)/1024/1024 from dba_data_files where tablespace_name = 'UNDOTBS1') total,
3 (select sum(bytes)/1024/1024 from dba_free_space where tablespace_name = 'UNDOTBS1') free
4 from dual;
TOTAL FREE
---------- ----------
2048 1960.3125
SQL> exit从 Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 - 64bit Production
With the Partitioning, Real Application Clusters, OLAP and Data Mining options 断开
$ rman target /
恢复管理器: Release 10.2.0.3.0 - Production on 星期六 9月 22 23:39:11 2007
Copyright (c) 1982, 2005, Oracle. All rights reserved.
连接到目标数据库: TESTRAC (DBID=4291216984)
RMAN> run
2> {
3> allocate channel c1 device type disk format '/data1/backup/%U';
4> backup tablespace undotbs1;
5> }
使用目标数据库控制文件替代恢复目录分配的通道: c1通道 c1: sid=301 实例=testrac1 devtype=DISK
启动 backup 于 22-9月 -07通道 c1: 启动全部数据文件备份集通道 c1: 正在指定备份集中的数据文件输入数据文件 fno=00002 name=+DISK/testrac/datafile/undotbs1.263.618591197通道 c1: 正在启动段 1 于 22-9月 -07通道 c1: 已完成段 1 于 22-9月 -07段句柄=/data1/backup/07isk6i2_1_1 标记=TAG20070922T233945 注释=NONE通道 c1: 备份集已完成, 经过时间:00:00:03完成 backup 于 22-9月 -07
启动 Control File and SPFILE Autobackup 于 22-9月 -07段 handle=/data/oracle/product/10.2/database/dbs/c-4291216984-20070922-00 comment=NONE完成 Control File and SPFILE Autobackup 于 22-9月 -07释放的通道: c1
RMAN> list backup of tablespace undotbs1;
备份集列表
===================
BS 关键字 类型 LV 大小 设备类型 经过时间 完成时间
------- ---- -- ---------- ----------- ------------ ----------
829 Full 88.10M DISK 00:00:03 22-9月 -07
BP 关键字: 1039 状态: AVAILABLE 已压缩: NO 标记: TAG20070922T233945段名:/data1/backup/07isk6i2_1_1
备份集 829 中的数据文件列表
文件 LV 类型 Ckp SCN Ckp 时间 名称
---- -- ---- ---------- ---------- ----
2 Full 5705040412 22-9月 -07 +DISK/testrac/datafile/undotbs1.263.618591197
从上面的测试看，UNDO表空间占有了80多M的空间，而备份的大小也是80多M。
再来看看11g的情况：
[oracle@yangtk ~]$ sqlplus yangtk/yangtk
SQL*Plus: Release 11.1.0.6.0 - Production on Sat Oct 27 23:31:58 2007
Copyright (c) 1982, 2007, Oracle. All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.1.0.6.0 - Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
SQL> select
2 (select sum(bytes)/1024/1024 from dba_data_files where tablespace_name = 'UNDOTBS1') total,
3 (select sum(bytes)/1024/1024 from dba_free_space where tablespace_name = 'UNDOTBS1') free
4 from dual;
TOTAL FREE
---------- ----------
400 279.75
SQL> host
[oracle@yangtk ~]$ rman target /
Recovery Manager: Release 11.1.0.6.0 - Production on Sat Oct 27 23:33:26 2007
Copyright (c) 1982, 2007, Oracle. All rights reserved.
connected to target database: ORA11G (DBID=4026820313)
RMAN> backup tablespace undotbs1;
Starting backup at 27-OCT-07
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=135 device type=DISK
channel ORA_DISK_1: starting full datafile backup set
channel ORA_DISK_1: specifying datafile(s) in backup set
input datafile file number=00003 name=/data/oracle/oradata/ora11g/ORA11G/datafile/o1_mf_undotbs1_3d379k48_.dbf
channel ORA_DISK_1: starting piece 1 at 27-OCT-07
channel ORA_DISK_1: finished piece 1 at 27-OCT-07
piece handle=/data1/backup/0hivj3mf_1_1 tag=TAG20071027T233335 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:16
Finished backup at 27-OCT-07
RMAN> list backup of tablespace undotbs1;
List of Backup Sets
===================
BS Key Type LV Size Device Type Elapsed Time Completion Time
------- ---- -- ---------- ----------- ------------ ---------------
16 Full 432.00K DISK 00:00:18 27-OCT-07
BP Key: 16 Status: AVAILABLE Compressed: NO Tag: TAG20071027T233335
Piece Name: /data1/backup/0hivj3mf_1_1
List of Datafiles in backup set 16
File LV Type Ckp SCN Ckp Time Name
---- -- ---- ---------- --------- ----
3 Full 4148196 27-OCT-07 /data/oracle/oradata/ora11g/ORA11G/datafile/o1_mf_undotbs1_3d379k48_.dbf
11g中，UNDO表空间占有了120M左右，但是备份的结果只有432K。
下面继续测试：
RMAN> exit
Recovery Manager complete.
[oracle@yangtk ~]$ exit
exit
SQL> CREATE TABLE T_BACKUP AS SELECT * FROM DBA_OBJECTS WHERE 1 = 2;
Table created.
SQL> INSERT INTO T_BACKUP SELECT * FROM DBA_OBJECTS;
68467 rows created.
SQL> INSERT INTO T_BACKUP SELECT * FROM T_BACKUP;
68467 rows created.
SQL> INSERT INTO T_BACKUP SELECT * FROM T_BACKUP;
136934 rows created.
SQL> INSERT INTO T_BACKUP SELECT * FROM T_BACKUP;
273868 rows created.
SQL> UPDATE T_BACKUP SET OWNER = OWNER;
547736 rows updated.
SQL> SELECT
2 (SELECT SUM(BYTES)/1024/1024 FROM DBA_DATA_FILES WHERE TABLESPACE_NAME = 'UNDOTBS1') TOTAL,
3 (SELECT SUM(BYTES)/1024/1024 FROM DBA_FREE_SPACE WHERE TABLESPACE_NAME = 'UNDOTBS1') FREE
4 FROM DUAL;
TOTAL FREE
---------- ----------
400 251.75
SQL> HOST
[oracle@yangtk ~]$ rman target /
Recovery Manager: Release 11.1.0.6.0 - Production on Sun Oct 28 00:06:19 2007
Copyright (c) 1982, 2007, Oracle. All rights reserved.
connected to target database: ORA11G (DBID=4026820313)
RMAN> backup tablespace undotbs1;
Starting backup at 28-OCT-07
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=00003 name=/data/oracle/oradata/ora11g/ORA11G/datafile/o1_mf_undotbs1_3d379k48_.dbf
channel ORA_DISK_1: starting piece 1 at 28-OCT-07
channel ORA_DISK_1: finished piece 1 at 28-OCT-07
piece handle=/data1/backup/0iivj5l1_1_1 tag=TAG20071028T000656 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:37
Finished backup at 28-OCT-07
RMAN> list backup of tablespace undotbs1;
List of Backup Sets
===================
BS Key Type LV Size Device Type Elapsed Time Completion Time
------- ---- -- ---------- ----------- ------------ ---------------
16 Full 432.00K DISK 00:00:18 27-OCT-07
BP Key: 16 Status: AVAILABLE Compressed: NO Tag: TAG20071027T233335
Piece Name: /data1/backup/0hivj3mf_1_1
List of Datafiles in backup set 16
File LV Type Ckp SCN Ckp Time Name
---- -- ---- ---------- --------- ----
3 Full 4148196 27-OCT-07 /data/oracle/oradata/ora11g/ORA11G/datafile/o1_mf_undotbs1_3d379k48_.dbf
BS Key Type LV Size Device Type Elapsed Time Completion Time
------- ---- -- ---------- ----------- ------------ ---------------
17 Full 28.05M DISK 00:00:40 28-OCT-07
BP Key: 17 Status: AVAILABLE Compressed: NO Tag: TAG20071028T000656
Piece Name: /data1/backup/0iivj5l1_1_1
List of Datafiles in backup set 17
File LV Type Ckp SCN Ckp Time Name
---- -- ---- ---------- --------- ----
3 Full 4165861 28-OCT-07 /data/oracle/oradata/ora11g/ORA11G/datafile/o1_mf_undotbs1_3d379k48_.dbf
Oracle会备份UNDO表空间中没有COMMIT的数据。如果将数据COMMIT后，会发现结果集又恢复了原来的大小：
RMAN> exit
Recovery Manager complete.
[oracle@yangtk ~]$ exit
exit
SQL> COMMIT;
Commit complete.
SQL> SELECT
2 (SELECT SUM(BYTES)/1024/1024 FROM DBA_DATA_FILES WHERE TABLESPACE_NAME = 'UNDOTBS1') TOTAL,
3 (SELECT SUM(BYTES)/1024/1024 FROM DBA_FREE_SPACE WHERE TABLESPACE_NAME = 'UNDOTBS1') FREE
4 FROM DUAL;
TOTAL FREE
---------- ----------
400 251.75
SQL> EXIT
Disconnected from Oracle Database 11g Enterprise Edition Release 11.1.0.6.0 - Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
[oracle@yangtk ~]$ rman target /
Recovery Manager: Release 11.1.0.6.0 - Production on Sun Oct 28 00:12:25 2007
Copyright (c) 1982, 2007, Oracle. All rights reserved.
connected to target database: ORA11G (DBID=4026820313)
RMAN> backup tablespace undotbs1;
Starting backup at 28-OCT-07
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=170 device type=DISK
channel ORA_DISK_1: starting full datafile backup set
channel ORA_DISK_1: specifying datafile(s) in backup set
input datafile file number=00003 name=/data/oracle/oradata/ora11g/ORA11G/datafile/o1_mf_undotbs1_3d379k48_.dbf
channel ORA_DISK_1: starting piece 1 at 28-OCT-07
channel ORA_DISK_1: finished piece 1 at 28-OCT-07
piece handle=/data1/backup/0jivj5vk_1_1 tag=TAG20071028T001236 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:15
Finished backup at 28-OCT-07
RMAN> list backup of tablespace undotbs1;
List of Backup Sets
===================
BS Key Type LV Size Device Type Elapsed Time Completion Time
------- ---- -- ---------- ----------- ------------ ---------------
16 Full 432.00K DISK 00:00:18 27-OCT-07
BP Key: 16 Status: AVAILABLE Compressed: NO Tag: TAG20071027T233335
Piece Name: /data1/backup/0hivj3mf_1_1
List of Datafiles in backup set 16
File LV Type Ckp SCN Ckp Time Name
---- -- ---- ---------- --------- ----
3 Full 4148196 27-OCT-07 /data/oracle/oradata/ora11g/ORA11G/datafile/o1_mf_undotbs1_3d379k48_.dbf
BS Key Type LV Size Device Type Elapsed Time Completion Time
------- ---- -- ---------- ----------- ------------ ---------------
17 Full 28.05M DISK 00:00:40 28-OCT-07
BP Key: 17 Status: AVAILABLE Compressed: NO Tag: TAG20071028T000656
Piece Name: /data1/backup/0iivj5l1_1_1
List of Datafiles in backup set 17
File LV Type Ckp SCN Ckp Time Name
---- -- ---- ---------- --------- ----
3 Full 4165861 28-OCT-07 /data/oracle/oradata/ora11g/ORA11G/datafile/o1_mf_undotbs1_3d379k48_.dbf
BS Key Type LV Size Device Type Elapsed Time Completion Time
------- ---- -- ---------- ----------- ------------ ---------------
18 Full 28.08M DISK 00:00:19 28-OCT-07
BP Key: 18 Status: AVAILABLE Compressed: NO Tag: TAG20071028T001236
Piece Name: /data1/backup/0jivj5vk_1_1
List of Datafiles in backup set 18
File LV Type Ckp SCN Ckp Time Name
---- -- ---- ---------- --------- ----
3 Full 4166069 28-OCT-07 /data/oracle/oradata/ora11g/ORA11G/datafile/o1_mf_undotbs1_3d379k48_.dbf
RMAN> backup tablespace undotbs1;
Starting backup at 28-OCT-07
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=00003 name=/data/oracle/oradata/ora11g/ORA11G/datafile/o1_mf_undotbs1_3d379k48_.dbf
channel ORA_DISK_1: starting piece 1 at 28-OCT-07
channel ORA_DISK_1: finished piece 1 at 28-OCT-07
piece handle=/data1/backup/0kivj7b8_1_1 tag=TAG20071028T003551 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:15
Finished backup at 28-OCT-07
RMAN> list backup of tablespace undotbs1;
List of Backup Sets
===================
BS Key Type LV Size Device Type Elapsed Time Completion Time
------- ---- -- ---------- ----------- ------------ ---------------
16 Full 432.00K DISK 00:00:18 27-OCT-07
BP Key: 16 Status: AVAILABLE Compressed: NO Tag: TAG20071027T233335
Piece Name: /data1/backup/0hivj3mf_1_1
List of Datafiles in backup set 16
File LV Type Ckp SCN Ckp Time Name
---- -- ---- ---------- --------- ----
3 Full 4148196 27-OCT-07 /data/oracle/oradata/ora11g/ORA11G/datafile/o1_mf_undotbs1_3d379k48_.dbf
BS Key Type LV Size Device Type Elapsed Time Completion Time
------- ---- -- ---------- ----------- ------------ ---------------
17 Full 28.05M DISK 00:00:40 28-OCT-07
BP Key: 17 Status: AVAILABLE Compressed: NO Tag: TAG20071028T000656
Piece Name: /data1/backup/0iivj5l1_1_1
List of Datafiles in backup set 17
File LV Type Ckp SCN Ckp Time Name
---- -- ---- ---------- --------- ----
3 Full 4165861 28-OCT-07 /data/oracle/oradata/ora11g/ORA11G/datafile/o1_mf_undotbs1_3d379k48_.dbf
BS Key Type LV Size Device Type Elapsed Time Completion Time
------- ---- -- ---------- ----------- ------------ ---------------
18 Full 28.08M DISK 00:00:19 28-OCT-07
BP Key: 18 Status: AVAILABLE Compressed: NO Tag: TAG20071028T001236
Piece Name: /data1/backup/0jivj5vk_1_1
List of Datafiles in backup set 18
File LV Type Ckp SCN Ckp Time Name
---- -- ---- ---------- --------- ----
3 Full 4166069 28-OCT-07 /data/oracle/oradata/ora11g/ORA11G/datafile/o1_mf_undotbs1_3d379k48_.dbf
BS Key Type LV Size Device Type Elapsed Time Completion Time
------- ---- -- ---------- ----------- ------------ ---------------
19 Full 424.00K DISK 00:00:16 28-OCT-07
BP Key: 19 Status: AVAILABLE Compressed: NO Tag: TAG20071028T003551
Piece Name: /data1/backup/0kivj7b8_1_1
List of Datafiles in backup set 19
File LV Type Ckp SCN Ckp Time Name
---- -- ---- ---------- --------- ----
3 Full 4166605 28-OCT-07 /data/oracle/oradata/ora11g/ORA11G/datafile/o1_mf_undotbs1_3d379k48_.dbf
最后两个备份都发生在COMMIT之后，唯一的区别在于一个是COMMIT刚刚结束，而第二个备份是过了一段时间才执行。
对于刚刚提交的内容，Oracle在备份的时候还无法确定是否被恢复所需要，只要过一段时间，UNDO备份的优化就生效了
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