OCP-1Z0-053-V13.02-2题

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

答案解析：

参考：http://docs.oracle.com/cd/E11882_01/server.112/e41573/autostat.htm#PFGRF94178

Moving Window Baseline

A moving window baseline corresponds to all AWR data that exists within the AWR retention period. This is useful when using adaptive thresholds because the database can use AWR data in the entire AWR retention period to compute metric threshold values.

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://blog.csdn.net/rlhua/article/details/16802303

移动窗口基线

Oracle Database 会自动维护一个系统定义的移动窗口基线。系统定义的移动窗口基线的默认窗口大小为当前的AWR 保留期（默认为八天）。如果计划使用自适应阈值，则可考虑使用较大的移动窗口（如30 天），以便精确地计算阈值。通过将移动窗口中的天数更改为等于或小于AWR 保留期中的天数的值，可以调整移动窗口基线的大小。因此，要增加移动窗口的大小，需要先相应地增加AWR 保留期。

这种系统定义的基线提供了一个现成的默认基线，EM 的性能屏幕可对照当前的数据库性能对性能进行比较。

注：在Oracle Database 11g中，快照数据的默认保留期已经从七天更改为八天，以确保捕获整周的性能数据。