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*fromv$version;

BANNER
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
OracleDatabase11gEnterpriseEditionRelease11.2.0.4.0-64bitProduction
PL/SQLRelease11.2.0.4.0-Production
CORE	11.2.0.4.0	Production
TNSforLinux:Version11.2.0.4.0-Production
NLSRTLVersion11.2.0.4.0-Production
--创建环境
zx@ORCL>insertintot1select*fromdba_segments;

5887rowscreated.

zx@ORCL>insertintot1select*fromdba_segments;

5887rowscreated.

zx@ORCL>insertintot1select*fromdba_segments;

5887rowscreated.

zx@ORCL>insertintot1select*fromdba_segments;

5887rowscreated.

zx@ORCL>insertintot1select*fromdba_segments;

5887rowscreated.

zx@ORCL>insertintot1select*fromdba_segments;

5887rowscreated.

zx@ORCL>insertintot1select*fromdba_segments;

5887rowscreated.

zx@ORCL>insertintot1select*fromdba_segments;

5887rowscreated.

zx@ORCL>insertintot1select*fromdba_segments;

5887rowscreated.

zx@ORCL>commit;

Commitcomplete.

zx@ORCL>deletefromt1;

288463rowsdeleted.

zx@ORCL>selectstatus,sum(bytes)/1024/1024fromdba_undo_extentsgroupbystatus;

STATUS			SUM(BYTES)/1024/1024
-----------------------------------------------
UNEXPIRED				9.125
EXPIRED				.4375
ACTIVE					89.125

zx@ORCL>commit;

Commitcomplete.

--两次备份undo表空间文件
RMAN>backupdatafile5;

Startingbackupat2016-12-2213:09:27
usingchannelORA_DISK_1
channelORA_DISK_1:startingfulldatafilebackupset
channelORA_DISK_1:specifyingdatafile(s)inbackupset
inputdatafilefilenumber=00005name=/u02/app/oracle/oradata/orcl/undotbs2_01.dbf
channelORA_DISK_1:startingpiece1at2016-12-2213:09:27
channelORA_DISK_1:finishedpiece1at2016-12-2213:09:28
piecehandle=/u02/app/oracle/product/11.2.4/db1/dbs/3aro4007_1_1tag=TAG20161222T130927comment=NONE
channelORA_DISK_1:backupsetcomplete,elapsedtime:00:00:01
Finishedbackupat2016-12-2213:09:28

StartingControlFileandSPFILEAutobackupat2016-12-2213:09:28
piecehandle=/u02/app/oracle/product/11.2.4/db1/dbs/c-1444351641-20161222-0fcomment=NONE
FinishedControlFileandSPFILEAutobackupat2016-12-2213:09:31
--查看备份后的文件大小
RMAN>listbackupofdatafile5;


ListofBackupSets
===================
--第一次备份文件大小99.27M
BSKeyTypeLVSizeDeviceTypeElapsedTimeCompletionTime
-----------------------------------------------------------------
87Full99.27MDISK00:00:032016-12-2212:11:54
BPKey:87Status:AVAILABLECompressed:NOTag:TAG20161222T121151
PieceName:/u02/app/oracle/product/11.2.4/db1/dbs/36ro3sk7_1_1
ListofDatafilesinbackupset87
FileLVTypeCkpSCNCkpTimeName
-------------------------------------------
5Full90420312016-12-2212:11:51/u02/app/oracle/oradata/orcl/undotbs2_01.dbf
--第二次备份文件大小2.16M
BSKeyTypeLVSizeDeviceTypeElapsedTimeCompletionTime
-----------------------------------------------------------------
89Full2.16MDISK00:00:012016-12-2212:34:42
BPKey:89Status:AVAILABLECompressed:NOTag:TAG20161222T123441
PieceName:/u02/app/oracle/product/11.2.4/db1/dbs/38ro3tv1_1_1
ListofDatafilesinbackupset89
FileLVTypeCkpSCNCkpTimeName
-------------------------------------------
5Full90425762016-12-2212:34:41/u02/app/oracle/oradata/orcl/undotbs2_01.dbf
--查看操作系统文件大小
[oracle@rhel6release]$ls-lh/u02/app/oracle/product/11.2.4/db1/dbs/36ro3sk7_1_1
-rw-r-----1oracleoinstall100MDec2212:11/u02/app/oracle/product/11.2.4/db1/dbs/36ro3sk7_1_1
[oracle@rhel6release]$ls-lh/u02/app/oracle/product/11.2.4/db1/dbs/38ro3tv1_1_1
-rw-r-----1oracleoinstall2.2MDec2212:34/u02/app/oracle/product/11.2.4/db1/dbs/38ro3tv1_1_1

这个新特性也有一些限制

- Compatible parametermust beset to 11.0 or higher
- Backup must use a disk or OSB channel
- For 'backup copy of <object>' or 'backup datafilecopy' thedatabase 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)

（编辑：李大同）

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