1、確定和檢查相關信息

SQL> select database_role,open_mode from v$database;

DATABASE_ROLE??? OPEN_MODE

---------------- --------------------

PHYSICAL STANDBY MOUNTED

數據庫處于mount狀態下，是物理standby

檢查當前模式是否在閃回的條件下

SQL> show parameter db_recovery_file_dest;

NAME???????????????????????????????? TYPE??????? VALUE

------------------------------------ ----------- ------------------------------

db_recovery_file_dest??????????????? string

db_recovery_file_dest_size?????????? big integer 0

SQL> select FLASHBACK_ON from v$database;

FLASHBACK_ON

------------------

NO

通過檢查，standby閃回沒有開啟，在進行切換時需要開啟閃回

2、對standby數據庫進行操作

--取消日志在standby端的應用

SQL> alter database recover managed standby database cancel;

Database altered.

--設置閃回區域和閃回大小

SQL> alter system set db_recovery_file_dest_size = 40g;

System altered.

SQL> alter system set db_recovery_file_dest = '/u01/db_recover';

System altered.

另外，創建閃回目錄

mkdir /u01/db_recover

chown -R oracle:oinstall /u01/db_recover

--切換到snap database狀態

SQL> shutdown immediate

ORA-01109: database not open

Database dismounted.

ORACLE instance shut down.

SQL> startup mount;

ORACLE instance started.

Total System Global Area 8551575552 bytes

Fixed Size????????????????? 2270360 bytes

Variable Size??????????? 2147486568 bytes

Database Buffers???????? 6392119296 bytes

Redo Buffers??????????????? 9699328 bytes

Database mounted.

SQL> alter database convert to snapshot standby;

Database altered.

SQL> select database_role,open_mode from v$database;

DATABASE_ROLE??? OPEN_MODE

---------------- --------------------

SNAPSHOT STANDBY MOUNTED

--打開數據庫

SQL> alter database open;

Database altered.

SQL> select database_role,open_mode from v$database;

DATABASE_ROLE??? OPEN_MODE

---------------- --------------------

SNAPSHOT STANDBY READ WRITE

可以看到數據庫已經處理可讀寫的狀態了

4、對snap database進行讀寫測試

--切換日志

SQL> alter system switch logfile;

System altered.

--建表測試

SQL> create table mytest as select * from dba_tables;

Table created.

SQL> create table mytest1 as select * from dba_tables;

Table created.

SQL> select count(*) from dba_tables;

COUNT(*)

----------

4622

SQL> drop table mytest purge;

Table dropped.

5、測試完成后，還原到physical standby

--關閉數據庫并切換到mount狀態

SQL> shutdown immediate;

Database closed.

Database dismounted.

ORACLE instance shut down.

SQL> startup mount;

ORACLE instance started.

Total System Global Area 8551575552 bytes

Fixed Size????????????????? 2270360 bytes

Variable Size??????????? 2147486568 bytes

Database Buffers???????? 6392119296 bytes

Redo Buffers??????????????? 9699328 bytes

Database mounted.

--切換到physical standby狀態

SQL> alter database convert to physical standby;

Database altered.

--關閉閃回

SQL> alter database flashback off;

Database altered.

--重新開啟數據庫physical standby模式

SQL> shutdown immediate;

ORA-01507: database not mounted

ORACLE instance shut down.

SQL> startup nomount;

ORACLE instance started.

Total System Global Area 8551575552 bytes

Fixed Size????????????????? 2270360 bytes

Variable Size??????????? 2147486568 bytes

Database Buffers???????? 6392119296 bytes

Redo Buffers??????????????? 9699328 bytes

SQL> alter database mount standby database;

Database altered.

SQL> alter database open read only;

Database altered.

SQL> ALTER DATABASE RECOVER MANAGED STANDBY DATABASE USING CURRENT LOGFILE DISCONNECT FROM SESSION NODELAY;

Database altered.

SQL> select database_role,open_mode from v$database;

DATABASE_ROLE??? OPEN_MODE

---------------- --------------------

PHYSICAL STANDBY READ ONLY WITH APPLY

--檢查剛才的表

SQL> select count(*) from mytest1;

select count(*) from mytest1

*

ERROR at line 1:

ORA-00942: table or view does not exist

剛才創建的mytest1表已經不存在了

6、說明

需要注意的點：

--10g中創建的還原點必須在閃回后進行刪除，否則閃回恢復區可能會被撐滿，導致DB Hang住。11g中不用擔心這個問題，在重新轉換為physical standby時會自動進行還原點刪除。

--在進行轉換時，需要設置閃回區

--物理standby是最高保護模式(maximum protection),是不能轉換為snapshot standby的.

--物理standby使用了standby redo log,在create restore point后,要alter system switch logfile，以保證還原點的scn在物理standby庫上是歸檔的,不然可能無法成功閃回到還原點.

--物理standby在切換為快照standby后,如果間隔很長時間,primary數據庫產生的大量的重做日志,這樣可以在轉換為物理standby后,通過對primary數據庫的增量備份并recover到物理standby,來加快物理standby的還原速度。

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