273.Which statements are true regarding the system-defined moving window baseline in Oracle Database 11g? (Choose all that apply.)
A. It does not allow you to change the moving window size.
B. Adaptive threshold functionalities use it by default to compute statistics.
C. It is created by default with the window size being equal to the AWR retention time.
D. It is created when the first snapshot is collected by the Automatic Workload Repository (AWR).
Answer: BC
答案解析：
参考：http://docs.oracle.com/cd/E11882_01/server.112/e41573/autostat.htm#PFGRF94179
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.