一、描述
DB版本：12.1.0.2
system版本：7.0

二、处理过程
1、报错，数据库启动就实例就会异常终止

ORA-00312: online log 3 thread 1: '+DATADG/ORCLDG/ONLINELOG/group_3.403.962961193'
ORA-00312: online log 3 thread 1: '+DATADG/ORCLDG/ONLINELOG/group_3.405.962961193'
Mon Jan 08 13:35:53 2018
USER (ospid: 15155): terminating the instance due to error 16014
Mon Jan 08 13:35:53 2018
System state dump requested by (instance=1, osid=15155), summary=[abnormal instance termination].
System State dumped to trace file /u01/app/oracle/diag/rdbms/orcldg/orcldg/trace/orcldg_diag_15110_20180108133553.trc
Mon Jan 08 13:35:53 2018
Dumping diagnostic data in directory=[cdmp_20180108133553], requested by (instance=1, osid=15155), summary=[abnormal instance termination].
Mon Jan 08 13:35:53 2018
Instance terminated by USER, pid = 15155
Mon Jan 08 13:39:58 2018
Starting ORACLE instance (normal) (OS id: 16121)
Mon Jan 08 13:39:58 2018
CLI notifier numLatches:3 maxDescs:519
Mon Jan 08 13:39:58 2018

2、处理过程

SQL> startup mount;
ORACLE instance started.

Total System Global Area 1241513984 bytes
Fixed Size                  2923872 bytes
Variable Size             452985504 bytes
Database Buffers          771751936 bytes
Redo Buffers               13852672 bytes
Database mounted.
SQL> 

SQL> select group#,sequence#,archived,status from v$log;

    GROUP#  SEQUENCE# ARC STATUS
---------- ---------- --- ----------------
         1        356 NO  INACTIVE
         3        355 NO  INACTIVE
         2        357 NO  CURRENT

SQL> alter database clear logfile  group 3 ; 
alter database clear logfile  group 3
*
ERROR at line 1:
ORA-00350: log 3 of instance orcldg (thread 1) needs to be archived
ORA-00312: online log 3 thread 1:
'+DATADG/ORCLDG/ONLINELOG/group_3.403.962961193'
ORA-00312: online log 3 thread 1:
'+DATADG/ORCLDG/ONLINELOG/group_3.405.962961193'

SQL> 

SQL> alter database clear unarchived  logfile  group 3 ;

Database altered.

SQL> alter database open;

Database altered.

3、说明
我这里是一个ADG，主库这样操作会导致GAP，备库需要增量恢复。