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HomeDatabaseMysql Tutorialoracle11GR2 dataguard SWITCHOVER FAILOVER

1. switch:用户主动切换; 2. failover:主库出现故障,强行切换; switchover:一般switchover切换都是计划中的切换,特点是切换后,不会丢失任何数据,而且这个过程是可逆的,整个dataguard环境不会被破坏,原来dataguard环境中的所有物理和逻辑standby都

1. switch:用户主动切换;
2. failover:主库出现故障,强行切换;

switchover:一般switchover切换都是计划中的切换,特点是切换后,不会丢失任何数据,而且这个过程是可逆的,整个dataguard环境不会被破坏,原来dataguard环境中的所有物理和逻辑standby都可以继续工作。
在进行dataguard的物理standby切换前需要注意:
1、确认主库和从库间网络连接通畅;
2、确认没有活动的会话连接在数据库中;
3、primary数据库处于打开的状态,standby数据库处于mount状态;
4、确保standby数据库处于archivelog模式;
5、如果设置了redo应用延迟,那么将这个设置去掉;
6、确保配置了主库和从库的初始化参数,使得切换完成后,dataguard机制可以顺利的运行。
switch切换过程:先主库再备库

主库:
由于主库处于open状态,有访问的,所以v$database视图中,switch_status为session active,而由primary切换到standby需要数据库为open状态,因此,执行切换命令时,带上with session shutdown选项即可。
执行完切换命令后,关闭数据库,重新启动数据库到mount状态等待日志传输,开启日志应用。
查看alert log可以看到主库做了哪些动作:主库断开所有session(未提交事务会回滚),备份控制文件,切换日志并归档,传输日志到备库,给备库一个End-Of-REDO的信号,切换为standby,重新启动到mount。
查看switchover状态:
SQL> select database_role,switchover_status from v$database;
附: A:switchover_status出现session active/not allowed
当出现session active的时候表示还有活动的session
SQL> alter database commit to switchover to physical standby with session shutdown;
SQL> shutdown immediate;
SQL> startup nomount;
SQL> alter database mount standby database;

备库:
确认是否可以切换为主库,如果switchover_status为recovery needed或switchover latent,需要apply完所有归档日志才能切换。如果是sessions active则带上with session shutdown选项。apply完所有日志后,即可切换为primary,然后打开数据库。

查看alert.log可以看到备库做了哪些动作:关闭arch进程,接收主库日志,接收到主库End-Of-REDO的信号,apply完所有日志,清空online redo log以便打开数据库,切换为primary,打开数据库。
SQL> select database_role,switchover_status from v$database;
SQL> alter database commit to switchover to primary with session shutdown;
ERROR at line 1:
ORA-16139: media recovery required
SQL> alter database recover managed standby database disconnect from session;
Database altered.
SQL> select database_role,switchover_status from v$database;
DATABASE_ROLE SWITCHOVER_STATUS
—————- ——————–
PHYSICAL STANDBYTO PRIMARY
SQL> alter database commit to switchover to primary with session shutdown;
Database altered.
SQL> shutdown immediate;
SQL> startup;

以上过程,由于主库断开所有session并归档,传输日志到备库,发给备库end-ofredo的信号,因此正常swithch时,是不会丢失数据的。
切换完成后可以在主库归档,验证一下是否切换成功,备库是否能正常接收日志。

开启日志应用:(主库-原备库)
SQL> alter database recover managed standby database using current logfile disconnect from session;

FailOver:当主库当掉,无法使用时,此时的切换即为failover,如果保护模式为最大性能模式,是可能丢失数据的。
备库端:
如果是最大保护和最大可用性模式,则可以直接在备库端执行failover切换。如果是最大性能模式,为了尽可能减少数据丢失,需要检查主库是否有日志没有传输到备库,手动传输备库进行注册和恢复。注意RAC环境下,归档日志是分线程的。

1. 停止日志应用
alter database recover managed standby database cancel;
2. 关闭standby日志传输
alter database recover managed standby database finish force;
3. 切换到primary
alter database commit to switchover to primary with session shutdown;
做这一步的时候,若存在gap,则会报ORA-16139:Switchover: Media recovery required – standby not in limbo 错误。
做测试的时候,若先起主库再起备库,且未等待备库相关日志传输完毕,就会出现这个问题。此时需要强制切换
alter database activate physical standby database;
4. 重启数据库到open状态

[oracle@testdb dev01]$ scp * oracle@192.168.0.8:/u01/archive/dev01dg
注册归档日志有如下两种方法,较为简单当然是用rman了,一次注册多个。
RMAN>catalog start with ‘/u01/archive/dev01′;
SYS@dev01dg>alter database register logfile ‘/u01/archive/dev01dg/arch_e8fe6364_1_712757927_460.dbf’;
apply归档日志也有两种方法。
SYS@dev01dg>alter database recover managed standby database disconnect from session;
Database altered.
SYS@dev01dg>recover standby database;
ORA-00279: change 2863819 generated at 03/20/2010 21:58:17 needed for thread 1
ORA-00289: suggestion : /u01/archive/dev01dg/arch_e8fe6364_1_712757927_461.dbf
ORA-00280: change 2863819 for thread 1 is in sequence #461
当手动apply完所有的日志后,就可以failover切换到primary了,但是要注意的是,由于备库没有收到主库的end-of-redo的信号,所以直接转换会报错,要求介质恢复,此时需要提交命令告诉备库,日志恢复已经finish,需要进行failover切换,注意switch时千万不要带有finish选项,否则就会变成failover了。
SYS@dev01dg> alter database commit to switchover to primary with session shutdown;
alter database commit to switchover to primary with session shutdown
*
ERROR at line 1:
ORA-16139: media recovery required
SYS@dev01dg> select database_role,switchover_status from v$database;
DATABASE_ROLE SWITCHOVER_STATUS
—————- ——————–
PHYSICAL STANDBYNOT ALLOWED
SYS@dev01dg>alter database recover managed standby databasefinish[force];
Database altered.
SYS@dev01dg> select database_role,switchover_status from v$database;
DATABASE_ROLE SWITCHOVER_STATUS
—————- ——————–
PHYSICAL STANDBYTO PRIMARY
SYS@dev01dg>alter database commit to switchover to primary with session shutdown;
Database altered.
SYS@dev01dg>alter database open;
Database altered.
SYS@dev01dg> select database_role,switchover_status from v$database;
DATABASE_ROLE SWITCHOVER_STATUS
—————- ——————–
PRIMARY SESSIONS ACTIVE
failover完成后,数据库其实是以resetlogs方式打开的,如果log_archive_format=’arch_%d_%t_%r_%s.dbf’,可以看到归档日志的文件名会有新的resetlogs ID和sequence number,以此与原有的归档日志进行区分。

补充11g官方文档处理顺序和操作语句
1、主库切换
SELECT SWITCHOVER_STATUS FROM V$DATABASE;
ALTER DATABASE COMMIT TO SWITCHOVER TO PHYSICAL STANDBY WITH SESSION SHUTDOWN;
shutdown immediate;
startup nomount;
alter database mount standby database;
2、备库切换
SELECT SWITCHOVER_STATUS FROM V$DATABASE;
ALTER DATABASE COMMIT TO SWITCHOVER TO PRIMARY WITH SESSION SHUTDOWN;
ALTER DATABASE OPEN;
3、开启应用(新备库–原主库)
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE USING CURRENT LOGFILE DISCONNECT FROM SESSION;

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