1、为什么要使用Startup Migrate
STARTUP MIGRATE was introduced in 9.2 as a mechanism to be sure that most everything that needs to be done to run an upgrade script or a patch script is done automatically. In the past, customers were expected to adjust certain initialization parameters prior to beginning an upgrade or applying a a patch, but most of this is now done automatically by STARTUP MIGRATE. When a customer starts a database in MIGRATE mode, the following ALTER SYSTEM commands will be set automatically:
ALTER SYSTEM ENABLE RESTRICTED SESSION;
ALTER SYSTEM SET “_SYSTEM_TRIG_ENABLED”=FALSE SCOPE=MEMORY;
ALTER SYSTEM SET _undo_autotune=FALSE SCOPE=MEMORY;
ALTER SYSTEM SET undo_retention=900 SCOPE=MEMORY;
ALTER SYSTEM SET JOB_QUEUE_PROCESSES=0 SCOPE=MEMORY;
ALTER SYSTEM SET AQ_TM_PROCESSES=0 SCOPE=MEMORY;
这些我们可以从数据库的Startup Migrate命令启动数据库的日志中可以看出来

Sun Oct  9 21:53:04 2011
ALTER SYSTEM enable restricted session;
Sun Oct  9 21:53:04 2011
ALTER SYSTEM SET _system_trig_enabled=FALSE SCOPE=MEMORY;
Autotune of undo retention is turned off. 
Sun Oct  9 21:53:04 2011
ALTER SYSTEM SET _undo_autotune=FALSE SCOPE=MEMORY;
Sun Oct  9 21:53:04 2011
ALTER SYSTEM SET undo_retention=900 SCOPE=MEMORY;
MMNL started with pid=12, OS id=8452
Sun Oct  9 21:53:04 2011
ALTER SYSTEM SET aq_tm_processes=0 SCOPE=MEMORY;
Sun Oct  9 21:53:04 2011
Resource Manager disabled during database migration: plan '' not set
Sun Oct  9 21:53:04 2011
ALTER SYSTEM SET resource_manager_plan='' SCOPE=MEMORY;
replication_dependency_tracking turned off (no async multimaster replication found)
Completed: ALTER DATABASE OPEN MIGRATE

2、Startup Migrate主用作用
在9i，无论升级/降级 数据库都是startup migrate
10g后增加了upgrade参数，升级可直接用startup upgrade，降级仍是startup migrate

3、Startup Migrate辅助作用（解决部分ORA-00701）

SQL> alter index I_H_OBJ#_COL# rebuild;
alter index I_H_OBJ#_COL# rebuild
*
ERROR at line 1:
ORA-00701: object necessary for warmstarting database cannot be altered

SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup migrate;
ORACLE instance started.
Total System Global Area 139531744 bytes
Fixed Size 452064 bytes
Variable Size 121634816 bytes
Database Buffers 16777216 bytes
Redo Buffers 667648 bytes
Database mounted.
Database opened.
SQL> alter index I_H_OBJ#_COL# rebuild;

Index altered.

SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup
ORACLE instance started.

Total System Global Area 139531744 bytes
Fixed Size 452064 bytes
Variable Size 121634816 bytes
Database Buffers 16777216 bytes
Redo Buffers 667648 bytes
Database mounted.
Database opened.