053-002

2.You plan to have a larger moving window size for the default system-defined moving window baseline
because you want to use the adaptive threshold.
Which statement factors in this consideration while increasing the size of the moving window.?
A. The collection level for the AWR should be set to BASIC.
B. The moving window size must be less than Undo Retention.
C. The moving window size should be greater than the Automatic Workload Repository (AWR) retention
period.
D. The moving window size should be equal to or less than the Automatic Workload Repository (AWR)
retention period.
Answer: D

解析:

The window_size parameter is used to specify the new window size, in number of days, for the default moving window size. In this example, the window_size parameter is set to 30. The window size must be set to a value that is equal to or less than the value of the AWR retention setting.To set a window size that is greater than the current AWR retention period, you must first increase the value of the retention parameter

Oracle Database automatically maintains a system-defined moving window baseline. The default window size for the system-defined moving window baseline is the current AWR retention period, which by default is 8 days. If you are planning to use adaptive thresholds, consider using a larger moving window—such as 30 days—to accurately compute threshold values. You can resize the moving window baseline by changing the number of days in the moving window to a value that is equal to or less than the number of days in the AWR retention period. Therefore, to increase the size of a moving window, you must first increase the AWR retention period accordingly.

参考:

http://docs.oracle.com/cd/B28359_01/server.111/b28274/autostat.htm#CHDICJHJ