对于数据卫士，您可以在物理备用和逻辑备用之间进行选择。让我们先来看一下两者 有哪些不同！我将首先演示物理备用，随后转换至逻辑备用（数据库也由此命名）：
[oracle@uhesse1 ~]$ dgmgrl sys/oracle@prima
DGMGRL for Linux: Version 11.2.0.1.0 - 64bit Production
Copyright (c) 2000, 2009, Oracle. All rights reserved.
Welcome to DGMGRL, type "help" for information.
Connected.
DGMGRL> show configuration;
Configuration - myconf
Protection Mode: MaxPerformance
Databases:
prima - Primary database
logst - Physical standby database
Fast-Start Failover: DISABLED
Configuration Status:
SUCCESS
到目前为止，logst仍然是物理备用。被称为物理备用的原因是，prima和logst的数据文件在物理上是相同的。我甚至可以从一个还原至另一个：
DGMGRL> edit database logst set state=apply-off;
Succeeded.
DGMGRL> exit
[oracle@uhesse1 ~]$ sqlplus sys/oracle@prima as sysdba
SQL*Plus: Release 11.2.0.1.0 Production on Fri Feb 20 11:43:07 2015
Copyright (c) 1982, 2009, Oracle. All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit Production
SYS@prima > select name from v$datafile where file#=4;
NAME
--------------------------------------------------
/u01/app/oracle/oradata/prima/users01.dbf
SYS@prima > alter database datafile 4 offline;
Database altered.
现在，我从备用服务器uhesse2中将数据文件复制到主服务器uhesse1，有不同的方法可以做到这一点，但scp是一个：
SYS@logst > select name from v$datafile where file#=4;
NAME
--------------------------------------------------
/u01/app/oracle/oradata/logst/users01.dbf
SYS@logst > exit
Disconnected from Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit Production
[oracle@uhesse2 ~]$ scp /u01/app/oracle/oradata/logst/users01.dbf uhesse1:/u01/app/oracle/oradata/prima/users01.dbf
The authenticity of host ‘uhesse1 (192.168.56.10)‘ can‘t be established.
RSA key fingerprint is e9:e7:5b:8b:b2:33:42:26:89:03:54:0c:16:0d:98:57.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added ‘uhesse1,192.168.56.10‘ (RSA) to the list of known hosts.
oracle@uhesse1‘s password:
users01.dbf 100% 5128KB 5.0MB/s 00:00
[oracle@uhesse2 ~]$
当我尝试将数据文件在prima上再次上线时，看起来就像我想从备份中将其恢复：
SYS@prima > alter database datafile 4 online;
alter database datafile 4 online
*
ERROR at line 1:
ORA-01113: file 4 needs media recovery
ORA-01110: data file 4: ‘/u01/app/oracle/oradata/prima/users01.dbf‘
SYS@prima > recover datafile 4;
Media recovery complete.
SYS@prima > alter database datafile 4 online;
Database altered.
在此处的两个站点中，数据文件和归档的日志文件在物理上都是相同的，只有控制文 件是不同的。 v$database（比如v$datafile）从控制文件获取其内容：
SYS@prima > select name,dbid,database_role from v$database;
NAME DBID DATABASE_ROLE
-------------------------------------------------- ---------- ----------------
PRIMA 2012613220 PRIMARY
SYS@prima > connect sys/oracle@logst as sysdba
Connected.
SYS@logst > select name,dbid,database_role from v$database;
NAME DBID DATABASE_ROLE
-------------------------------------------------- ---------- ----------------
PRIMA 2012613220 PHYSICAL STANDBY
现在，我要将其转换至逻辑备用：
DGMGRL> edit database logst set state=apply-off;
Succeeded.
DGMGRL> exit
[oracle@uhesse1 ~]$ sqlplus sys/oracle@prima as sysdba
SQL*Plus: Release 11.2.0.1.0 Production on Fri Feb 20 17:29:16 2015
Copyright (c) 1982, 2009, Oracle. All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit Production
SYS@prima > exec dbms_logstdby.build
PL/SQL procedure successfully completed.
SYS@prima > connect sys/oracle@logst as sysdba
Connected.
SYS@logst > alter database recover to logical standby logst;
Database altered.
SYS@logst > shutdown immediate
ORA-01507: database not mounted
ORACLE instance shut down.
SYS@logst > startup mount
ORACLE instance started.
Total System Global Area 521936896 bytes
Fixed Size 2214936 bytes
Variable Size 314573800 bytes
Database Buffers 201326592 bytes
Redo Buffers 3821568 bytes
Database mounted.
SYS@logst > alter database open resetlogs;
Database altered.
SYS@logst > select name,dbid,database_role from v$database;
NAME DBID DATABASE_ROLE
-------------------------------------------------- ---------- ----------------
LOGST 3156487356 LOGICAL STANDBY
SYS@logst > exit
Disconnected from Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit Production
[oracle@uhesse1 ~]$ dgmgrl sys/oracle@prima
DGMGRL for Linux: Version 11.2.0.1.0 - 64bit Production
Copyright (c) 2000, 2009, Oracle. All rights reserved.
Welcome to DGMGRL, type "help" for information.
Connected.
DGMGRL> remove database logst;
Removed database "logst" from the configuration
DGMGRL> add database logst as connect identifier is logst;
Database "logst" added
DGMGRL> enable database logst;
Enabled.
DGMGRL> show configuration;
Configuration - myconf
Protection Mode: MaxPerformance
Databases:
prima - Primary database
logst - Logical standby database
Fast-Start Failover: DISABLED
Configuration Status:
SUCCESS
一处重要的改变是， DBID和名称现已不同于上面看到的主数据库。数据文件在物理上也不再是相同的：
DGMGRL> edit database logst set state=apply-off;
Succeeded.
DGMGRL> exit
[oracle@uhesse1 ~]$ sqlplus sys/oracle@prima as sysdba
SQL*Plus: Release 11.2.0.1.0 Production on Fri Feb 20 17:38:56 2015
Copyright (c) 1982, 2009, Oracle. All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit Production
SYS@prima > alter database datafile 4 offline;
Database altered.
SYS@prima > select name from v$datafile where file#=4;
NAME
--------------------------------------------------
/u01/app/oracle/oradata/prima/users01.dbf
SYS@prima > host cp /u01/app/oracle/oradata/prima/users01.dbf /u01/app/oracle/oradata/prima/users01.old
我复制原始文件的原 因是，我知道从logst恢复将不起作用。为了证明我的观点：
[oracle@uhesse2 ~]$ scp /u01/app/oracle/oradata/logst/users01.dbf uhesse1:/u01/app/oracle/oradata/prima/users01.dbf
oracle@uhesse1‘s password:
users01.dbf 100% 5128KB 5.0MB/s 00:00
SYS@prima > alter database datafile 4 online;
alter database datafile 4 online
*
ERROR at line 1:
ORA-01122: database file 4 failed verification check
ORA-01110: data file 4: ‘/u01/app/oracle/oradata/prima/users01.dbf‘
ORA-01206: file is not part of this database - wrong database id
没错，logst现在是一个自主数据库，它只是偶然地使用与prima（几乎）相同的DML。它在Oracle数据块方面已不再与prima相同。对于logst来说，来自于prima的rowids已不再有意义：
DGMGRL> edit database logst set state=apply-on;
Succeeded.
SYS@prima > insert into scott.dept values (50,‘TEST‘,‘TEST‘);
insert into scott.dept values (50,‘TEST‘,‘TEST‘)
*
ERROR at line 1:
ORA-00376: file 4 cannot be read at this time
ORA-01110: data file 4: ‘/u01/app/oracle/oradata/prima/users01.dbf‘
SYS@prima > host cp /u01/app/oracle/oradata/prima/users01.old /u01/app/oracle/oradata/prima/users01.dbf
SYS@prima > alter database datafile 4 online;
alter database datafile 4 online
*
ERROR at line 1:
ORA-01113: file 4 needs media recovery
ORA-01110: data file 4: ‘/u01/app/oracle/oradata/prima/users01.dbf‘
SYS@prima > recover datafile 4;
Media recovery complete.
SYS@prima > alter database datafile 4 online;
Database altered.
SYS@prima > insert into scott.dept values (50,‘TEST‘,‘TEST‘);
1 row created.
SYS@prima > commit;
Commit complete.
SYS@prima > select rowid,dept.* from scott.dept where deptno=50;
ROWID DEPTNO DNAME LOC
------------------ ---------- -------------- -------------
AAADS8AAEAAAACNAAE 50 TEST TEST
这就是我们通常记录在重做日志条目中的rowid，在我们进行“Redo Apply”（“恢复数据库”的另一种术语）时，该rowid足以在主数据库上以及一个物理备用上对该行进行检索。但这个rowid在logst上是不同的：
SYS@logst > connect sys/oracle@logst as sysdba
Connected.
SYS@logst > select rowid,dept.* from scott.dept where deptno=50;
ROWID DEPTNO DNAME LOC
------------------ ---------- -------------- -------------
AAADS8AAEAAAACOAAA 50 TEST TEST
这就是为什么我们需要将附加信息（补充日志数据）放入主数据库的重做日志条 目中。这将帮助SQL Apply机制对该行进行检索：
逻辑备用架构
补充日志数据应至少额外包括上图中的主键。在没有主键的情况下，修改行的每 一列将被写入重做日志。 这将影响主数据库的性能。逻辑备用的另一个严重缺点是，SQL Apply机制并不支持每个数据类型和每个在主数据库上的操作。然而，不支持的数据类型数量随着版本的升级正在逐渐减少。
原文：http://blog.itpub.net/12798004/viewspace-1692815/