我们在关闭数据库时，数据库日志会记录以下信息：

Fri Dec 25 12:14:55 2009
Shutting down instance: further logons disabled
Fri Dec 25 12:14:56 2009
Stopping background process CJQ0
Fri Dec 25 12:14:56 2009
Stopping background process QMNC
Fri Dec 25 12:14:58 2009
Stopping background process MMNL
Fri Dec 25 12:14:59 2009
Stopping background process MMON
Fri Dec 25 12:15:00 2009
Shutting down instance (immediate)
License high water mark = 112
All dispatchers and shared servers shutdown
Fri Dec 25 12:15:05 2009
ALTER DATABASE CLOSE NORMAL

记录了从数据库启动到数据库关闭前用户连接数的最高峰，和查询v$license视图字段sessions_highwater值一样

 SQL> select sessions_max s_max, sessions_warning s_warning,
         sessions_current s_current, sessions_highwater s_high, users_max
         from v$license;

              S_MAX   S_WARNING   S_CURRENT      S_HIGH   USERS_MAX
         ----------  ----------  ----------  ----------  ----------
                  0           0           6           6           0

所以通过这个值，我们可以确定当前连接数是否正常，如果这个值突然很大，那我们就要检查应用。

可以参考metalink ID 1034330.6

License high water mark in alert log
  文档 ID:  注释:1034330.6 类型:  BULLETIN
  上次修订日期:  28-JUN-2007 状态:  PUBLISHED

ABSTRACT
  What does the license high water mark represent in the "alert.log"?

SCOPE & APPLICATION
  General information for DBAs.

License High Water Mark in Alert Log:
=====================================

When shutting down the database, you notice various numbers being generated for
the license high water mark. According to the 8i Server Reference Guide, the
license high water mark number in the column of v$license represents the
highest number of concurrent users sessions since the instance started.
         

    Example:

    Shutting down instance (normal)
    License high water mark = 3

You can query the V$LICENSE data dictionary view for the high water mark, it is
sessions_highwater column.  Also, the current limits for all of the license
settings, the current number of sessions, and the maximum number of concurrent
sessions for the instance can be queried in V$LICENSE.

    SQL> select sessions_max s_max, sessions_warning s_warning,
         sessions_current s_current, sessions_highwater s_high, users_max
         from v$license;

              S_MAX   S_WARNING   S_CURRENT      S_HIGH   USERS_MAX
         ----------  ----------  ----------  ----------  ----------
                  0           0           6           6           0