如下面的测试用例：
确定开始随机连接到的是实例2，然后杀掉实例2，
此时查询select instance_name, status from v$instance;，会报错ORA-25408，
再次查询，发现已经自动failover到实例1。
C:\Documents and Settings\Administrator>sqlplus jingyu/jingyu@linuxidc
SQL*Plus: Release 11.2.0.1.0 Production on Tue Jul 28 11:04:13 2015
Copyright (c) 1982, 2010, Oracle. All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, Real Application Clusters, Automatic Storage Management,
OLAP,
Data Mining and Real Application Testing options
SQL> select instance_name, status from v$instance;
INSTANCE_NAME STATUS
---------------- ------------
linuxidc2 OPEN
SQL> select instance_name, status from v$instance;
select instance_name, status from v$instance
*
ERROR at line 1:
ORA-25408: can not safely replay call
SQL> select instance_name, status from v$instance;
INSTANCE_NAME STATUS
---------------- ------------
linuxidc1 OPEN