DataGuard之DG 故障切换（switchover和failover）以及利用flashback 进行恢复

淡淡的烟草味﹌ 2022-07-12 07:40 249阅读 0赞

本次实验是基于之前的DG环境，具体环境搭建可参考：

http://blog.csdn.net/shiyu1157758655/article/details/55253132

我们配置DG的目的就是为了在主库出现故障时，备库能够提供服务，保证业务的正常运行。DG的故障切换分为switchover和failover两种:

### a)switchover ###

### 是用户有计划的进行停机切换，能够保证不丢失数据，下面我们来看下switchover是怎样操作的： ###

登录主库

$sqlplus / as sysdba

SQL> select switchover\_status from v$database;（查看主库状态）

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查询结果是TO STANDBY  或 SESSIONS ACTIVE表明可以进行切换；

SQL> ALTER DATABASE COMMITTO SWITCHOVER TO PHYSICAL STANDBY;

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SQL>shutdown immediate;

SQL> startup mount;

SQL> select database\_role from v$database;

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登录备库：

$sqlplus / as sysdba

SQL> SELECT SWITCHOVER\_STATUS FROM V$DATABASE;

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TO PRIMARY 或 SESSIONS ACTIVE表明可以切换成主库；

现在可以把备库切换成主库了

SQL> alter database committo switchover to primary with session shutdown;

SQL> ALTER DATABASE OPEN;

SQL> select switchover\_status,database\_role,open\_mode from v$database;

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从上图可以看出，我们已经switchover切换成功了！

记住：这时候要在现在的备库上开启同步：

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

### b)FAILOVER    ###

为了能够在failover后能够恢复DG,需要在主库上开启flashback

关于开启flashback 可以参考：

[http://blog.csdn.net/shiyu1157758655/article/details/55095760][http_blog.csdn.net_shiyu1157758655_article_details_55095760]

如果不开启flashback的话，DG就要重新搭建

由于主库已经不可访问，我们所有的操作都在备库完成：

SQL> alter database recover managed standbydatabase cancel;

SQL> alter database recover managed standby database finish force;

SQL> select database\_role from v$database;

SQL> alter database commit to switchover toprimary;

SQL> alter database open; 或者 shutdown immediate+startup

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现在利用flashback重建ＤＧ

在新的主库上执行下面操作：

SQL> select to\_char(standby\_became\_primary\_scn) from v$database;

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在之前的主库上，也就是现在的备库上执行下面的操作:

SQL>startup mount

SQL> flashback database to scn  9978113; //这个值为在新主库上查询到的SCN值

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;

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至此failover 切换和切换过如何恢复就已经完成

如果有配置错误还请不啬指出，欢迎加入oracle qq群： 425614362

[Center]: /images/20220711/40bec86d7f374bc7a05598565e97004f.png
[Center 1]: /images/20220711/2a54e398326c435788486d78bd7c07fe.png
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[http_blog.csdn.net_shiyu1157758655_article_details_55095760]: http://blog.csdn.net/shiyu1157758655/article/details/55095760
[Center 5]: /images/20220711/cd59e17c6e2a4130adb4ca9510267108.png
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