042关于alter问题
151. View the Exhibit to examine the output of the DBA_OUTSTANDING_ALERT view.
After 30 minutes, you executed the following command:
SQL> SELECT reason,metric_value FROM dba_outstanding_alerts;
REASON
METRIC_VALUE
-------------------------------------------------------
----------------------
Tablespace [TEST] is [28 percent] full
28.125
What could be the two reasons for the elimination of the other rows in the output? (Choose two.)
A) The threshold alert conditions are cleared.
B) The threshold alerts are transferred to DBA_ALERT_HISTORY.
C) The non-threshold-based alerts are transferred to DBA_ALERT_HISTORY.
D) The threshold alerts related to database metrics are permanently stored in
DBA_ALERT_HISTORY but not the threshold alerts related to instance metrics
答案：AB
理解不来这道题，麻烦大师们解释下。
经过参考这个 http://empo007.itpub.net/post/12076/465449 和
http://space.itpub.net/?471666/viewspace-217128
先搞清 ：
DBA_OUTSTANDING_ALERTS ：
描述了oracle数据库认为是突出的警告。当向 Flash Recovery中添加或删除文件等变化都将记录在数据库的 alert 日志中，Oracle 10g 也针对该新特性提供了一个新的视 图 ，通过该视图可以得到相关的信息。
dba_alert_history：
代表了不在突出的有时间限制的历史告警
threshold_alert ：
是超过备份阈值时引发的警报
ORACLE的一些内部组件可以周期性进行监控的动作，对发现的问题产生相应的alert信息。alert信息的产生是基于一些threshold值或者特定事件。基于threshold的alert信息会自DBA_OUTSTANDING_ALERTS视图中找到，当被clear的时候，这些状态的警告会进入DBA_ALERT_HISTORY
来自 “ ITPUB博客 ” ，链接：https://blog.itpub.net/450962/viewspace-1027697/ ，如需转载，请注明出处，否则将追究法律责任。
