一、dg的搭建、计划切换、故障切换：
https://blog.csdn.net/shiyu1157758655/article/details/72878249
其中搭建有如下两点需要注意：
1）备库密码文件跟实例名一样，而不是跟db_unique_name一样，如下（而不是orapwdgstd）：

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[oracle@dg2 dbs]$ ll
-rw-r----- 1 oracle oinstall 1536 Dec 11 15:56 orapwdg

2）主库和备份的tns文件都需要加上(UR = A)参数：

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DGSTD =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = localhost)(PORT = 1521))
(CONNECT_DATA =
(SERVER = DEDICATED)
(SERVICE_NAME = dgstd)
(UR = A)
)
)

二、switchover
主库：

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SQL> select switchover_status,database_role from v$database;
SWITCHOVER_STATUS DATABASE_ROLE
-------------------- ----------------
TO STANDBY PRIMARY
SQL> alter database commit to switchover to physical standby;
SQL> startup mount
SQL> select database_role from v$database;
DATABASE_ROLE
----------------
PHYSICAL STANDBY

备库：

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SQL>select switchover_status,database_role from v$database;
SWITCHOVER_STATUS DATABASE_ROLE
-------------------- ----------------
TO PRIMARY PHYSICAL STANDBY
SQL>alter database commit to switchover to primary with session shutdown;
SQL>alter database open;
SQL>select switchover_status,database_role,open_mode from v$database;
SWITCHOVER_STATUS DATABASE_ROLE OPEN_MODE
-------------------- ---------------- --------------------
RESOLVABLE GAP PRIMARY READ WRITE

新备库（原主库）：

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SQL> alter database open;
SQL> alter database recover managed standby database using current logfile disconnect from session;

三、failover（必须确保主库备库的flashback是打开的，可查看v$database(flashback_on)）
第一阶段（故障）：
主库：

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SQL> select switchover_status,database_role,open_mode from v$database;
SWITCHOVER_STATUS DATABASE_ROLE OPEN_MODE
-------------------- ---------------- --------------------
TO STANDBY PRIMARY READ WRITE
SQL> shutdown abort

备库：

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SQL> alter database recover managed standby database cancel;
SQL> alter database recover managed standby database finish force;
SQL> select switchover_status,database_role,open_mode from v$database;
SWITCHOVER_STATUS DATABASE_ROLE OPEN_MODE
-------------------- ---------------- --------------------
TO PRIMARY PHYSICAL STANDBY READ ONLY
SQL> alter database commit to switchover to primary;
SQL> alter database open;
SQL> select switchover_status,database_role,open_mode from v$database;
SWITCHOVER_STATUS DATABASE_ROLE OPEN_MODE
-------------------- ---------------- --------------------
FAILED DESTINATION PRIMARY READ WRITE

第二阶段（恢复）：
新主库：

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SQL> select to_char(standby_became_primary_scn) from v$database;
TO_CHAR(STANDBY_BECAME_PRIMARY_SCN)
----------------------------------------
1022901

新备库：

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SQL> startup mount
SQL> flashback database to scn 1022901;
SQL> alter database convert to physical standby;
SQL> shutdown immediate
SQL> startup
SQL> alter database recover managed standby database using current logfile disconnect from session;
SQL> select open_mode from v$database;
OPEN_MODE
--------------------
READ ONLY WITH APPLY

四、dg的启动和关闭：
1、启动：先启动standby库在启动primary库
备库：

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[oracle@dg2 ~]$ lsnrctl start
SQL> startup #此时会自动启动成READ ONLY模式，可以查看v$database(OPEN_MODE)
SQL> alter database recover managed standby database using current logfile disconnect from session;

主库：

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[oracle@dg1 ~]$ lsnrctl start
SQL> startup

2、关闭：先关闭primary库再关闭standby库
主库：

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SQL> shutdown immediate

备库：

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SQL> alter database recover managed standby database cancel;
SQL> shutdown immediate

3、验证是否正常：

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SQL> col dest_name format a30
SQL> col error format a20
SQL> select dest_name,error from v$archive_dest; #查看是否有报错

五、dg相关知识点：
http://lib.csdn.net/article/oracle/29298

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