生产环境中，可能会有各种各样的原因导致数据库不能提供服务，例如数据库库的硬件故障，操作系统故障或软件bug，人为的失误(例如rm -rf /)等，在这种情况下，dataguard显得尤为重要，当主库不可用的时候，可以将备库failover成主库继续提供服务，failover和switchover不同的是，执行failover后，原有的dataguard配置将会失效且有可能会丢失部分数据，所以在生产环境中能用switchover解决的问题则应尽量采用switchover！switchover执行过程参考：http://ylw6006.blog.51cto.com/470441/849829
一：使用sql命令执行failover
1：查看当前的主库是dg1，物理备库为dg2，将主库关闭，模拟主库故障
- [oracle@dg2 ~]$ dgmgrl /
- DGMGRL for Linux: Version 11.2.0.3.0 - 64bit Production
- Copyright (c) 2000, 2009, Oracle. All rights reserved.
- Welcome to DGMGRL, type "help" for information.
- Connected.
- DGMGRL> show configuration;
- Configuration - DG_BROKER_CONFIG
- Protection Mode: MaxAvailability
- Databases:
- dg1 - Primary database
- dg2 - Physical standby database
- Fast-Start Failover: DISABLED
- Configuration Status:
- SUCCESS
- SQL> select open_mode,database_role,db_unique_name,flashback_on from v$database;
- OPEN_MODE DATABASE_ROLE DB_UNIQUE_NAME FLASHBACK_ON
- -------------------- ---------------- -------------------- ------------------
- READ WRITE PRIMARY dg1 NO
- SQL> shutdown abort
- ORACLE instance shut down.
2：在备库dg2上执行failover过程，failover执行的命令和switchover类似，只是在这个过程中，主库已经不可用
- SQL> select open_mode,database_role,db_unique_name,flashback_on from v$database;
- OPEN_MODE DATABASE_ROLE DB_UNIQUE_NAME FLASHBACK_ON
- -------------------- ---------------- -------------------- ------------------
- READ ONLY WITH APPLY PHYSICAL STANDBY dg2 NO
- SQL> alter database recover managed standby database cancel;
- Database altered.
- SQL> select open_mode,database_role,db_unique_name,flashback_on from v$database;
- OPEN_MODE DATABASE_ROLE DB_UNIQUE_NAME FLASHBACK_ON
- -------------------- ---------------- -------------------- ------------------
- READ ONLY PHYSICAL STANDBY dg2 NO
- 出现这个错误说明日志并未完全的应用
- SQL> alter database commit to switchover to primary;
- alter database commit to switchover to primary
- *
- ERROR at line 1:
- ORA-16139: media recovery required
- SQL> alter database recover managed standby database using current logfile disconnect from session;
- Database altered.
- SQL> select open_mode,database_role,db_unique_name,flashback_on from v$database;
- OPEN_MODE DATABASE_ROLE DB_UNIQUE_NAME FLASHBACK_ON
- -------------------- ---------------- -------------------- ------------------
- READ ONLY WITH APPLY PHYSICAL STANDBY dg2 NO
- SQL> alter database recover managed standby database finish;
- Database altered.
- SQL> alter database commit to switchover to primary;
- Database altered.
- SQL> select open_mode,database_role,db_unique_name,flashback_on from v$database;
- OPEN_MODE DATABASE_ROLE DB_UNIQUE_NAME FLASHBACK_ON
- -------------------- ---------------- -------------------- ------------------
- MOUNTED PRIMARY dg2 NO
- SQL> alter database open;
- Database altered.
- SQL> select open_mode,database_role,db_unique_name,flashback_on from v$database;
- OPEN_MODE DATABASE_ROLE DB_UNIQUE_NAME FLASHBACK_ON
- -------------------- ---------------- -------------------- ------------------
- READ WRITE PRIMARY dg2 NO
二：使用datagurad broker进行failover
1:开启主库和备库的闪回功能，主要用于主库恢复后的reinstate操作，当前主库为dg2,备库为dg1
- SQL> select open_mode,database_role,db_unique_name,flashback_on from v$database;
- OPEN_MODE DATABASE_ROLE DB_UNIQUE_NAME FLASHBACK_ON
- -------------------- ---------------- -------------------- ------------------
- READ WRITE PRIMARY dg2 YES
- SQL> select open_mode,database_role,db_unique_name,flashback_on from v$database;
- OPEN_MODE DATABASE_ROLE DB_UNIQUE_NAME FLASHBACK_ON
- -------------------- ---------------- -------------------- ------------------
- READ ONLY WITH APPLY PHYSICAL STANDBY dg1 YES
- [oracle@dg1 ~]$ dgmgrl sys/123456@dg1
- DGMGRL for Linux: Version 11.2.0.3.0 - 64bit Production
- Copyright (c) 2000, 2009, Oracle. All rights reserved.
- Welcome to DGMGRL, type "help" for information.
- Connected.
- DGMGRL> show configuration;
- Configuration - DG_BROKER_CONFIG
- Protection Mode: MaxAvailability
- Databases:
- dg2 - Primary database
- dg1 - Physical standby database
- Fast-Start Failover: DISABLED
- Configuration Status:
- SUCCESS
2:关闭主库dg2,模拟主库故障
- SQL> select open_mode,database_role,db_unique_name,flashback_on from v$database;
- OPEN_MODE DATABASE_ROLE DB_UNIQUE_NAME FLASHBACK_ON
- -------------------- ---------------- -------------------- ------------------
- READ WRITE PRIMARY dg2 YES
- SQL> shutdown abort
- ORACLE instance shut down.
- DGMGRL> show configuration;
- Configuration - DG_BROKER_CONFIG
- Protection Mode: MaxAvailability
- Databases:
- dg2 - Primary database
- dg1 - Physical standby database
- Fast-Start Failover: DISABLED
- Configuration Status:
- ORA-01034: ORACLE not available
- ORA-16625: cannot reach database "dg2"
- DGM-17017: unable to determine configuration status
3：执行failover
- DGMGRL> failover to dg1;
- Performing failover NOW, please wait...
- Failover succeeded, new primary is "dg1"
- DGMGRL> show configuration;
- Configuration - DG_BROKER_CONFIG
- Protection Mode: MaxAvailability
- Databases:
- dg1 - Primary database
- Warning: ORA-16629: database reports a different protection level from the protection mode
- dg2 - Physical standby database (disabled)
- ORA-16661: the standby database needs to be reinstated
- Fast-Start Failover: DISABLED
- Configuration Status:
- WARNING
4:重新启动原主库dg2
- SQL> startup
- ORACLE instance started.
- Total System Global Area 417546240 bytes
- Fixed Size 2228944 bytes
- Variable Size 352324912 bytes
- Database Buffers 54525952 bytes
- Redo Buffers 8466432 bytes
- Database mounted.
- ORA-16649: possible failover to another database prevents this database from
- being opened
- SQL> select open_mode,database_role,db_unique_name,flashback_on from v$database;
- OPEN_MODE DATABASE_ROLE DB_UNIQUE_NAME FLASHBACK_ON
- -------------------- ---------------- -------------------- ------------------
- MOUNTED PRIMARY dg2 YES
5:执行reinstate操作
- DGMGRL> reinstate database dg2;
- Reinstating database "dg2", please wait...
- Operation requires shutdown of instance "dg" on database "dg2"
- Shutting down instance "dg"...
- ORA-01109: database not open
- Database dismounted.
- ORACLE instance shut down.
- Operation requires startup of instance "dg" on database "dg2"
- Starting instance "dg"...
- Unable to connect to database
- ORA-12514: TNS:listener does not currently know of service requested in connect descriptor
- Failed.
- Warning: You are no longer connected to ORACLE.
- Please complete the following steps and reissue the REINSTATE command:
- start up and mount instance "dg" of database "dg2"
- SQL> conn /as sysdba
- Connected to an idle instance.
- SQL> startup
- ORACLE instance started.
- Total System Global Area 417546240 bytes
- Fixed Size 2228944 bytes
- Variable Size 352324912 bytes
- Database Buffers 54525952 bytes
- Redo Buffers 8466432 bytes
- Database mounted.
- Database opened.
- SQL> select open_mode,database_role,db_unique_name,flashback_on from v$database;
- OPEN_MODE DATABASE_ROLE DB_UNIQUE_NAME FLASHBACK_ON
- -------------------- ---------------- -------------------- ------------------
- READ ONLY PHYSICAL STANDBY dg2 YES
- DGMGRL> show configuration;
- Configuration - DG_BROKER_CONFIG
- Protection Mode: MaxAvailability
- Databases:
- dg1 - Primary database
- dg2 - Physical standby database (disabled)
- ORA-16661: the standby database needs to be reinstated
- Fast-Start Failover: DISABLED
- Configuration Status:
- SUCCESS
- DGMGRL> enable database dg2;
- Error: ORA-16661: the standby database needs to be reinstated
- Failed.
- DGMGRL> reinstate database dg2;
- Reinstating database "dg2", please wait...
- Reinstatement of database "dg2" succeeded
- DGMGRL> show configuration;
- Configuration - DG_BROKER_CONFIG
- Protection Mode: MaxAvailability
- Databases:
- dg1 - Primary database
- dg2 - Physical standby database
- Fast-Start Failover: DISABLED
- Configuration Status:
- SUCCESS
总结
1：非到万不得已的情况，不使用failover，优先考虑switchover
2：若执行failover，则考虑使用sql命令完成
3：执行failover后，应及时备份数据，并重构dg环境