环境：RHEL6.5 + Oracle11.2.0.4 双节点RAC
故障现象：节点1实例没有启动成功，节点2正常启动。

1.故障现象 尝试启动RAC 节点1，遭遇ORA-01105，ORA-01606： ``` SQL> startup mount; ORACLE instance started.

Total System Global Area 9.4869E+10 bytes
Fixed Size 2264056 bytes
Variable Size 5.0197E+10 bytes
Database Buffers 4.4560E+10 bytes
Redo Buffers 109174784 bytes
ORA-01105: mount is incompatible with mounts by other instances
ORA-01606: parameter not identical to that of another mounted instance

数据库节点1目前状态是NOMOUNT.

<h1 >2.解决过程</h1>
**错误代码说明：**

$ oerr ora 1105
01105, 00000, "mount is incompatible with mounts by other instances"
// *Cause: An attempt to mount the database discovered that another instance
// mounted a database by the same name, but the mount is not
// compatible. Additional errors are reported explaining why.
// *Action: See accompanying errors.

$ oerr ora 1606
01606, 00000, "parameter not identical to that of another mounted instance"
// *Cause: A parameter was different on two instances.
// *Action: Modify the initialization parameter and restart.

查询gc_隐含参数

    set linesize 333
    col name for a35
    col description for a66
    col value for a30
    SELECT   i.ksppinm name,  
       i.ksppdesc description,  
       CV.ksppstvl VALUE
    FROM   sys.x$ksppi i, sys.x$ksppcv CV  
       WHERE   i.inst_id = USERENV ('Instance')  
       AND CV.inst_id = USERENV ('Instance')  
       AND i.indx = CV.indx  
       AND i.ksppinm LIKE '/_gc%' ESCAPE '/'  
    ORDER BY   REPLACE (i.ksppinm, '_', '');  

查询结果如下（部分相同值的参数已省略）：

--节点1：
_gc_policy_time how often to make object policy decisions in minutes 0
_gc_read_mostly_flush_check if TRUE, optimize flushes for read mostly objects FALSE
_gc_read_mostly_locking if TRUE, enable read-mostly locking FALSE

--节点2：
_gc_policy_time how often to make object policy decisions in minutes 10
_gc_read_mostly_flush_check if TRUE, optimize flushes for read mostly objects FALSE
_gc_read_mostly_locking if TRUE, enable read-mostly locking TRUE

发现问题，_gc_policy_time隐藏参数，_gc_read_mostly_locking隐藏参数，2个节点值不一致。
解决方法：根据现在正常运行的节点2的值，重新设置这两个值：

alter system set "_gc_read_mostly_locking"=true scope=spfile sid='';
alter system set "_gc_policy_time"=10 scope=spfile sid='';
--正常关闭节点1：
shutdown immediate;
--正常启动节点1：
startup

实际执行过程如下：

SQL> alter system set "_gc_read_mostly_locking"=true scope=spfile sid='*';

System altered.

SQL> alter system set "_gc_policy_time"=10 scope=spfile sid='*';

System altered.

SQL> shutdown immediate;
ORA-01507: database not mounted

ORACLE instance shut down.
SQL> startup
ORACLE instance started.

Total System Global Area 9.4869E+10 bytes
Fixed Size 2264056 bytes
Variable Size 5.1271E+10 bytes
Database Buffers 4.3487E+10 bytes
Redo Buffers 109174784 bytes
Database mounted.
Database opened.

至此RAC节点1启动成功。

<h1 id="3">3.总结</h1>
猜测故障原因应该是之前有人修改数据库隐含参数，误操作只修改了一个实例导致。
当我们操作RAC环境时，一定要注意`sid='*'`这一点。