有哪些RAC环境中需要完整down库(Not rolling fashion)才能修改的参数，这个问题，在oracle的文档中也没有很好的说明。我们处理的时候，一般都是case by case。
之前队友们有过讨论，究竟哪些参数是需要完整down库的。
猜想一：ISINSTANCE_MODIFIABLE
SQL> show parameter process
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
processes integer 150
SQL> alter system set processes=200 scope=spfile sid='ora11g1';
System altered.
SQL>
SQL> exit
Disconnected from 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
[oracle@rac1 ~]$
[oracle@rac1 ~]$ srvctl stop instance -d ora11g -n rac1 ;
[oracle@rac1 ~]$
[oracle@rac1 ~]$
[oracle@rac1 ~]$
[oracle@rac1 ~]$ ps -ef |grep ora_
oracle 10751 9141 0 10:21 pts/1 00:00:00 grep ora_
[oracle@rac1 ~]$
[oracle@rac1 ~]$
[oracle@rac1 ~]$ srvctl start instance -d ora11g -n rac1 ;
[oracle@rac1 ~]$
[oracle@rac1 ~]$ sqlplus "/ as sysdba"
SQL*Plus: Release 11.2.0.4.0 Production on Mon May 9 10:27:24 2016
Copyright (c) 1982, 2013, 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> show parameter process
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
processes integer 200
processor_group_name string
SQL>
SQL> select inst_id,NAME,VALUE,ISINSTANCE_MODIFIABLE from gv$parameter where name='processes';
INST_ID NAME VALUE ISINS
---------- -------------------- ------------------------------ -----
1 processes 200 FALSE
2 processes 150 FALSE
SQL>
结论，并不是所有ISINSTANCE_MODIFIABLE=FALSE的参数都需要完整down库才能修改。不能完全参考这个标准。
猜想二：在线文档中提到的参数。但是抽查几个参数，也并不是所有的这些参数需要完整down库才能修改。
--(1)测试db_domain：
SQL> alter system set db_domain='mydomain' scope=spfile sid='ora11g2';
[oracle@rac2 ~]$ srvctl stop instance -d ora11g -n rac2
[oracle@rac2 ~]$ srvctl start instance -d ora11g -n rac2
[oracle@rac2 ~]$
SQL>
SQL> l
1* select inst_id,NAME,VALUE,ISINSTANCE_MODIFIABLE from gv$parameter where name='db_domain' order by 1
SQL> /
INST_ID NAME VALUE ISINS
---------- -------------------- ------------------------------ -----
1 db_domain FALSE
2 db_domain mydomain FALSE
SQL>
--(2)测试parallel_max_servers：
SQL> alter system set parallel_max_servers=100 scope=spfile sid='ora11g2';
System altered.
SQL> exit
Disconnected from Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, Real Application Clusters, Automatic Storage Management, OLAP,
Data Mining and Real Application Testing options
[oracle@rac2 ~]$
[oracle@rac2 ~]$
[oracle@rac2 ~]$ srvctl stop instance -d ora11g -n rac2
[oracle@rac2 ~]$ srvctl start instance -d ora11g -n rac2
SQL> l
1* select inst_id,NAME,VALUE,ISINSTANCE_MODIFIABLE from gv$parameter where name='parallel_max_servers' order by 1
SQL> /
INST_ID NAME VALUE ISINS
---------- -------------------- ------------------------------ -----
1 parallel_max_servers 80 TRUE
2 parallel_max_servers 100 TRUE
SQL>
结论，也并不是所有Parameters that Must Have Identical Settings on All Instances的参数都需要完整down库才能修改。也不能完全参考这个标准。
我们在如下这个文档中看到有相关的说法（但也不是指出了所有需要完全down库的参数，只是列举了几个）：How to change the DB_FILES parameter in RAC (Doc ID 1636681.1)
Certain INIT parameters must have the same value across all active instances.
For example, these include but are not restricted to, the following parameters:
ACTIVE_INSTANCE_COUNT, CLUSTER_DATABASE_INSTANCES, COMPATIBLE, CONTROL_FILES, DB_FILES, DB_NAME, DB_UNIQUE_NAME, UNDO_MANAGEMENT
None of these parameters can be changed in a RAC rolling fashion.
另外，我们禁用DRM的时候，涉及到如下参数：
Disable DRM：
(1)
_gc_affinity_time=0（10g）/_gc_policy_time=0（11g）
注：_gc_affinity_time has been rename to _gc_policy_time in 11g
(2)
_gc_undo_affinity =FALSE
当使用上述2个参数，禁用DRM的时候，也是需要完整down库的。
综上，case by case，我们总结目前RAC环境中已知的需要完全down的参数有（非完整列表，如果还有其他的，欢迎补充）:
ACTIVE_INSTANCE_COUNT
CLUSTER_DATABASE_INSTANCES
COMPATIBLE
CONTROL_FILES
DB_FILES
DB_NAME
DB_UNIQUE_NAME
UNDO_MANAGEMENT
_gc_affinity_time=0（10g）/_gc_policy_time=0（11g）
_gc_undo_affinity