激活dg库，供开发测试使用。

----1, 确认备库已关闭job参数: job_queue_processes=0，一定要设成0！！
----2, 主库不用做操作。
----3, 激活备库后，备库成了一个独立的可读写库，与主库无关联。
----4, 主库暂时修改log_archive_stat_2=defer.
----5, 特殊情况：如果是激活二级备库，LOG_FILE_NAME_CONVERT要有主库到二级备库的路径转换对应，否则报ORA-16157错误，处理方法：把主库的路径加到LOG_FILE_NAME_CONVERT参数里

1.查看是否备库是否managed real time apply（in primary）

SQL> SELECT RECOVERY_MODE FROM V$ARCHIVE_DEST_STATUS WHERE DEST_ID=2;

RECOVERY_MODE
-----------------------
MANAGED REAL TIME APPLY

如果不是，设置如下（in standby）：

ALTER DATABASE RECOVER MANAGED STANDBY DATABASE CANCEL;
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE USING CURRENT LOGFILE DISCONNECT;

2.备库禁止job（in standby）：<<<<<!!!!!

alter system set job_queue_processes=0 scope=both sid='*';

3.确定主备间没有gap存在

（in primary）

select thread#, sequence# from v$thread;
SELECT STATUS, GAP_STATUS FROM V$ARCHIVE_DEST_STATUS WHERE DEST_ID = 2;

（in standby）

select process, status, thread#, sequence# from v$managed_standby where process='MRP0';

4.备库切换成主库（in standby）

4.1 查看备库状态是否是 TO PRIMARY

set line 300
col db_unique_name for a30
col open_mode for a20
col switchover_status for a30
col database_role for a20
select db_unique_name, database_role, open_mode,switchover_status from v$database;


DB_UNIQUE_NAME                 DATABASE_ROLE        OPEN_MODE            SWITCHOVER_STATUS
------------------------------ -------------------- -------------------- ------------------------------
oradg                     PHYSICAL STANDBY     READ ONLY WITH APPLY   NOT ALLOWED

4.2 激活备库（failover方式）

alter database recover managed standby database cancel;
alter database recover managed standby database finish;             ---------> 等待所有日志应用完成

select db_unique_name,database_role,open_mode,switchover_status from v$database;
DB_UNIQUE_NAME                 DATABASE_ROLE        OPEN_MODE            SWITCHOVER_STATUS
------------------------------ -------------------- -------------------- ------------------------------
oradg                     PHYSICAL STANDBY     READ ONLY            TO PRIMARY


alter database commit to switchover to primary with session shutdown;

4.3 再次检查job,确保关闭

show parameter job_queue_processes

4.4 open新主库

alter database open;

4.5 查询新主库状态

select db_unique_name, database_role, open_mode,switchover_status from v$database;

DB_UNIQUE_NAME                 DATABASE_ROLE    OPEN_MODE            SWITCHOVER_STATUS
------------------------------ ---------------- -------------------- --------------------
oradg                       PRIMARY          READ WRITE           FAILED DESTINATION

4.6 删除dblink

select case when owner <> 'PUBLIC' then 'create or replace procedure ' ||owner||'.drop_link as' || chr(10) ||
'begin execute immediate ''drop database link '||db_link ||''';' || chr(10) ||
'end;' ||chr(10) ||
'/' || chr(10) ||
'exec '||owner||'.drop_link;' || chr(10) ||
'drop procedure ' ||owner||'.drop_link;'
else 'drop public database link ' || db_link || ';' end from dba_db_links;