一、步骤
1.关闭节点二
2.配置相关参数
3.关闭节点1
4.启用闪回
5.打开节点二

二、操作过程

[root@rac01 ~]# su - oracle
Last login: Thu Jan  4 10:33:31 CST 2018 on pts/2
$sqlplus / as sysdba

SQL*Plus: Release 12.1.0.2.0 Production on Fri Jan 5 18:52:55 2018

Copyright (c) 1982, 2014, Oracle.  All rights reserved.

Connected to:
Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production
With the Partitioning, Real Application Clusters, Automatic Storage Management, OLAP,
Advanced Analytics and Real Application Testing options

SYS@orcl1> 
SYS@orcl1> 
SYS@orcl1> 
SYS@orcl1> show parameter recovery

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
db_recovery_file_dest                string
db_recovery_file_dest_size           big integer 0
recovery_parallelism                 integer     0
SYS@orcl1> show parameter flashback

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
db_flashback_retention_target        integer     1440
SYS@orcl1> alter system set db_recovery_file_dest_size=1g;

System altered.

SYS@orcl1> archive log list;
Database log mode              Archive Mode
Automatic archival             Enabled
Archive destination            +DATADG
Oldest online log sequence     121
Next log sequence to archive   122
Current log sequence           122
SYS@orcl1> alter system set db_recovery_file_dest='+datadg';

System altered.

SYS@orcl1> alter system set db_flashback_retention_target=2880;

System altered.

SYS@orcl1> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SYS@orcl1> startup mount;
ORACLE instance started.

Total System Global Area 1241513984 bytes
Fixed Size                  2923872 bytes
Variable Size             620757664 bytes
Database Buffers          603979776 bytes
Redo Buffers               13852672 bytes
Database mounted.
SYS@orcl1> alter database flashback on;

Database altered.

SYS@orcl1> alter database open;

Database altered.

SYS@orcl1> select flashback_on from v$database;

FLASHBACK_ON
------------------
YES

SYS@orcl1> show parameter recovery

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
db_recovery_file_dest                string      +datadg
db_recovery_file_dest_size           big integer 1G
recovery_parallelism                 integer     0
SYS@orcl1> show parameter flashback

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
db_flashback_retention_target        integer     2880
SYS@orcl1> 

小结：
生产环境ADG备库开闪回解决逻辑错误。未来再添加一个备库，做灾备，一主两备哈