今天在启动数据库的时候，发现database起不来了，停在了nomount状态，检查alert.log
ARCH: STARTING ARCH PROCESSES
ARC0 started with pid=8
ARC0: Archival started
ARC1 started with pid=9
ARC1: Archival started
Fri Jun 25 00:07:52 2004
ARCH: STARTING ARCH PROCESSES COMPLETE
Fri Jun 25 00:07:52 2004
ARC1: Thread not mounted <-------
Fri Jun 25 00:07:52 2004
ARC0: Thread not mounted <-------
Fri Jun 25 00:07:54 2004
ARC0: Thread not mounted <-------
不知道是什么原因，数据库停在了nomount状态，后来
sql> alter database mount ;
sql> alter database open;
问题解决了。
metalink原因如下：

THE INFORMATION IN THIS ARTICLE APPLIES TO:
          Oracle Server - Enterprise Edition - Version: 9.2.0.4
          This problem can occur on any platform.
SYMPTOMS:
        While doing the startup of the database it simply hangs at the mount stage.
CAUSE:
          From the Alert.log
=============
ARCH: STARTING ARCH PROCESSES
ARC0 started with pid=8
ARC0: Archival started
ARC1 started with pid=9
ARC1: Archival started
Fri Jun 25 00:07:52 2004
ARCH: STARTING ARCH PROCESSES COMPLETE
Fri Jun 25 00:07:52 2004
ARC1: Thread not mounted <-------
Fri Jun 25 00:07:52 2004
ARC0: Thread not mounted <-------
Fri Jun 25 00:07:52 2004

NOTE: This can happen if multiple archive processes are running. A lock conflict may result. This is not considered a bug within development.
FIX:
Open another sql*plus session
Login as sysdba
Shutdown abort
Startup