（ 1 ） 查看 主库状态
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SQL> select db_unique_name,open_mode,database_role,switchover_status from v$database;
DB_UNIQUE_NAME OPEN_MODE DATABASE_ROLE SWITCHOVER_STATUS
--------------- -------------------- ---------------- --------------------
bhtc db READ WRITE PRIMARY TO STANDBY
（ 2 ）主库执行切换命令
SQL> alter database commit to switchover to physical standby with session shutdown wait;
Database altered.
（ 2 ）重启主库角色变为备库（ mount 状态 ）
SQL> startup mount;
ORACLE instance started.
Total System Global Area 1.3429E+10 bytes
Fixed Size 2265944 bytes
Variable Size 6878661800 bytes
Database Buffers 6543114240 bytes
Redo Buffers 4612096 bytes
Database mounted.
（ 4 ）查看 主库状态
SQL> select db_unique_name,open_mode,database_role,switchover_status from v$database;
DB_UNIQUE_NAME OPEN_MODE DATABASE_ROLE SWITCHOVER_STATUS
--------------- -------------------- ---------------- --------------------
Bhtc db MOUNTED PHYSICAL STANDBY RECOVERY NEEDED
2. 备库切换成主库 （ B 机）
（ 1 ）查看备库状态
SQL> select db_unique_name,open_mode,database_role,switchover_status from v$database;
DB_UNIQUE_NAME OPEN_MODE DATABASE_ROLE SWITCHOVER_STATUS
--------------- -------------------- ---------------- --------------------
bhtcdg MOUNTED PHYSICAL STANDBY TO PRIMARY
（ 2 ）将备库切换成主库
SQL> alter database commit to switchover to primary with session shutdown wait ;
Database altered.
（ 3 ）查看备库状态
SQL> select db_unique_name,open_mode,database_role,switchover_status from v$database;
DB_UNIQUE_NAME OPEN_MODE DATABASE_ROLE SWITCHOVER_STATUS
--------------- -------------------- ---------------- --------------------
bhtcdg
MOUNTED
PRIMARY
NOT ALLOWED
（ 4 ）开启
SQL> alter database open;
Database altered.
SQL> select db_unique_name,open_mode,database_role,switchover_status from v$database;
DB_UNIQUE_NAME OPEN_MODE DATABASE_ROLE SWITCHOVER_STAT
--------------- ---------- ---------------- ---------------
bhtcdg READ WRITE PRIMARY RESOLVABLE GAP
3. 打开数据库（ A 机）
SQL> alter database open read only;
4. 应用日志（ A 机）
SQL> alter database recover managed standby database using current logfile disconnect from session;
3. 验证数据
（ 1 ）在新主库创建用户（ B 机）
SQL> create user test1 identified by test1;
SQL> commit;
SQL> alter system switch logfile;
System altered.
（ 2 ）在新备库查看（ A 机）
SQL> select username from dba_users where username='TEST1';
USERNAME
------------------------------
TEST1
4. 切换回 最初的状态
(1) 新 主库操作（ B 机 ）
SQL> alter database commit to switchover to physical standby with session shutdown;
Database altered.
SQL> startup mount;
ORACLE instance started.
Total System Global Area 1.3429E+10 bytes
Fixed Size 2265944 bytes
Variable Size 6878661800 bytes
Database Buffers 6543114240 bytes
Redo Buffers 4612096 bytes
Database mounted.
（2） 新 备库 操作（ A 机）
SQL> alter database commit to switchover to primary with session shutdown;
Database altered.
SQL> alter database open;
Database altered.
SQL> select db_unique_name,open_mode,database_role,switchover_status from v$database;
DB_UNIQUE_NAME OPEN_MODE DATABASE_ROLE SWITCHOVER_STATUS
--------------- -------------------- ---------------- --------------------
bhtcdb READ WRITE PRIMARY RESOLVABLE GAP
（ 3 ） B 机 操作
SQL> select db_unique_name,open_mode,database_role,switchover_status from v$database;
DB_UNIQUE_NAME OPEN_MODE DATABASE_ROLE SWITCHOVER_STATUS
-------------------- -------------------- ---------------- --------------------
bhtcdg MOUNTED PHYSICAL STANDBY NOT ALLOWED
（ 4 ）打开备库开启实时同步
SQL> alter database open read only;
Database altered.
SQL> alter database recover managed standby database using current logfile disconnect;
Database altered.
SQL> select db_unique_name,open_mode,database_role,switchover_status from v$database;
DB_UNIQUE_NAME OPEN_MODE DATABASE_ROLE SWITCHOVER_STAT
--------------- ---------- ---------------- ---------------
bhtcdg READ ONLY PHYSICAL STANDBY NOT ALLOWED
WITH APPLY
（ 5 ）再次查看 A 机
SQL> select db_unique_name,open_mode,database_role,switchover_status from v$database;
DB_UNIQUE_NAME OPEN_MODE DATABASE_ROLE SWITCHOVER_STATUS
--------------- -------------------- ---------------- --------------------
bhtc db READ WRITE PRIMARY TO STANDBY
此时 ，已经切换回最初的状态
（ 6 ）备库查看日志应用情况
SQL> select sequence#,applied from v$archived_log;
SEQUENCE# APPLIED
---------- ---------
8 YES
7 YES
9 YES
10 YES
11 YES
12 YES
13 YES
13 YES
14 YES
14 YES
15 YES
SEQUENCE# APPLIED
---------- ---------
15 YES
16 YES
16 YES
17 YES
17 NO
18 YES
19 YES
20 YES
21 IN-MEMORY
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