ocp 052考試詳解：1Z0-V8.02-第49題
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49. View the Exhibit to examine the output of the DBA_OUTSTANDING_ALERTS 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 perce 28.125 nt] full
What could be the reason for the elimination of the other rows in the output?
A.An Automatic Workload Repository snapshot has been taken recently.
B.The non-threshold-based alerts are transferred to DBA_ALERT_HISTORY.
C.The threshold alerts conditions are cleared and the 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.
Answer: C
答案解析：
服務器生成預警分為兩種類型：閾值預警和非閾值預警。
大多數服務器生成的預警是通過對數據庫度量設置警告閾值和嚴重閾值來配置的。可為120 多個度量定義閾值，這些度量包括：
·每秒的物理讀取次數
·每秒的用戶提交次數
·SQL 服務響應時間
除了表空間的空間占用率度量與數據庫相關外，其它度量都與實例相關。閾值預警又稱為“有狀態預警”，清空預警條件后，會自動清空這些預警。有狀態預警顯示在
DBA_OUTSTANDING_ALERTS中，清空后會轉到DBA_ALERT_HISTORY。
服務器生成的其它預警對應于特定的數據庫事件，如ORA-*錯誤、“快照太舊”錯誤、“恢復區空閑空間過少”和“可恢復會話被掛起”等。這些都不是基于閾值的預警，又稱
為“無狀態預警”。無狀態預警會直接轉到歷史記錄表。只在Database Control 環境中，清空無狀態預警才有意義，因為Database Control 會在自身的資料檔案庫中存儲無狀態預警。
