Oracle 11g UNDO表空间备份增强:
前面提到,由于UNDO表空间在恢复时不可缺少,所以在进行备份时必须备份该表空间,但是一旦事务提交,修改被确认,则该事务的前镜像被标记为INACTIVE,其中的信息在恢复时也就不会被用到,如果在备份时能够跳过这些数据,则备份UNDO表空间的效率就可以大大提高。
在Oracle Database 11g中,Oracle引入了一个新的特性RMAN UNDO备份优化。在RMAN备份UNDO表空间时,提交事务的UNDO信息将不备份,这个特性随RMAN强制启用。在测试中,一个395MB的UNDO表空间备份文件的大小仅为10.06M:
sys@TQGZS11G> select file#,name,ceil(bytes/1024/1024) MB,status from v$datafile;
FILE# NAME MB STATUS
---------- -------------------------------------------------- ---------- ----------
1 /oracle/oradata/tqgzs11g/system01.dbf 740 SYSTEM
2 /oracle/oradata/tqgzs11g/sysaux01.dbf 645 ONLINE
3 /oracle/oradata/tqgzs11g/undotbs01.dbf 395 ONLINE
4 /oracle/oradata/tqgzs11g/users01.dbf 13 ONLINE
5 /oracle/oradata/tqgzs11g/example01.dbf 100 ONLINE
6 /oracle/oradata/tqgzs11g/TQ.dbf 100 ONLINE
6 rows selected.[oracle@rhel52: ~]$rman target /
[uniread] Loaded history (5 lines)
Recovery Manager: Release 11.1.0.7.0 - Production on Sat Dec 26 20:41:37 2009
Copyright (c) 1982, 2007, Oracle. All rights reserved.
connected to target database: TQGZS11G (DBID=3743726461)RMAN> backup datafile 3 format '/oracle/rmanbk/undotbs_%d_%T_%s_%p.bak';
Starting backup at 26-DEC-09
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=138 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=/oracle/oradata/tqgzs11g/undotbs01.dbf
channel ORA_DISK_1: starting piece 1 at 26-DEC-09
channel ORA_DISK_1: finished piece 1 at 26-DEC-09
piece handle=/oracle/rmanbk/undotbs_TQGZS11G_20091226_2_1.bak tag=TAG20091226T204142 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:07
Finished backup at 26-DEC-09RMAN> list backup;
List of Backup Sets
===================
BS Key Type LV Size Device Type Elapsed Time Completion Time
------- ---- -- ---------- ----------- ------------ ---------------
1 Full 10.06M DISK 00:00:04 26-DEC-09
BP Key: 1 Status: AVAILABLE Compressed: NO Tag: TAG20091226T204142
Piece Name: /oracle/rmanbk/undotbs_TQGZS11G_20091226_2_1.bak
List of Datafiles in backup set 1
File LV Type Ckp SCN Ckp Time Name
---- -- ---- ---------- --------- ----
3 Full 1065943 26-DEC-09 /oracle/oradata/tqgzs11g/undotbs01.dbf
这一特性是许多DBA期待已久的,在一个繁忙的生产环境中,UNDO表空间可能占用几十GB的空间,全部备份显然并不合理,现在Oracle 11g解决了这个问题。
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