DATA GUARD 主备切换

一、Switchover正常切换
1、主库
（1）、查看主库状态及角色
SQL> select name,database_role from v$database;

NAME   DATABASE_ROLE

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

ORCL   PRIMARY
SQL> select switchover_status from v$database;

SWITCHOVER_STATUS

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

TO STANDBY
（2）、查看归档日志是否有中断
SQL> select status,gap_status from v$archive_dest_status where dest_id=2;

STATUS   GAP_STATUS

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

VALID   NO GAP
（3）、提前查看备库状态
SQL> select switchover_status,name from v$database;

 

SWITCHOVER_STATUS    NAME

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

NOT ALLOWED      ORCL
（4）、切换到备库，数据库会自动关闭，启动到mount状态
SQL> alter database commit to switchover to physical standby;

Database altered.
SQL> startup mount;

ORACLE instance started.

Total System Global Area 1258291200 bytes

Fixed Size     8620224 bytes

Variable Size   872417088 bytes

Database Buffers   369098752 bytes

Redo Buffers     8155136 bytes

Database mounted.
（5）、查询数据库状态及角色
SQL> select database_role from v$database;

DATABASE_ROLE

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

PHYSICAL STANDBY
2、备库
（1）、查询数据库角色及状态
SQL> select name,database_role from v$database;

NAME   DATABASE_ROLE

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

ORCL   PHYSICAL STANDBY
SQL> select switchover_status from v$database;

SWITCHOVER_STATUS

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

TO PRIMARY
（2）、切换到主库，此时是mount状态
SQL> alter database commit to switchover to primary;

Database altered.

SQL> alter database open;

Database altered.
（3）、开启数据库查询角色信息
SQL> select name,DATABASE_ROLE from v$database;

NAME   DATABASE_ROLE

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

ORCL   PRIMARY
3、新备库
（1）、打开数据库，查看数据库状态
SQL> alter database open;

Database altered.

 
SQL> select open_mode from v$database;

OPEN_MODE

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

READ ONLY
（2）、应用日志，查看数据库状态
SQL>alter database recover managed standby database using current logfile disconnect from session;sion;

Database altered.
SQL> select open_mode from v$database;

OPEN_MODE

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

READ ONLY WITH APPLY
4、验证数据同步

二、failover
是当主库不可用的时候，强制性把备库切换成主库，以继续提供数据库服务，此时主库已经崩掉，在备库操作
1、确认日志是否同步
SQL> SELECT THREAD#, LOW_SEQUENCE#, HIGH_SEQUENCE# FROM V$ARCHIVE_GAP;

no rows selected

如果日志不同步可以使用
ALTER DATABASE REGISTER PHYSICAL LOGFILE '缺失日志文件';
2、查询日志是否应用到最新状态
select distinct thread#,max(sequence#) over(partition by thread#) a from v$archived_log;
3、切换到主库
SQL> alter database recover managed standby database finish force;

Database altered.
SQL> alter database commit to switchover to primary;                               
SQL> alter database commit to switchover to primary;

Database altered.
SQL> alter database open;

Database altered.
SQL> select name,database_role from v$database;

NAME   DATABASE_ROLE

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

ORCL   PRIMARY
成功切换到主库，此时DG环境已经损坏，需要重新构建。

 
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作者：吴用丶
来源：优快云
原文：https://blog.youkuaiyun.com/weixin_42774383/article/details/82682503
版权声明：本文为博主原创文章，转载请附上博文链接！