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042-108

原创 Linux操作系统 作者:jbymy2000 时间:2012-03-15 10:09:11 0 删除 编辑
108. In your database, the snapshot interval is set to 10 minutes for the Automatic Workload Repository (AWR). The database instance is running for the past 30 days
View the Exhibit to examine the Automatic Database Diagnostic Monitor (ADDM) task.
The ADDM task is performed every 10 minutes,except the last task.What could be the reason for this?
A. The snapshot retention period for the AWR was increased before the last task. B. The optimizer statistics for few objects in the database were locked before the last task. C. The STATISTICS_LEVEL initialization parameter was changed to BASIC and reset to T
YPICAL before the last task. D. The optimizer statistics was collected manually by using the DBMS_STATS package before the last task.
答案:C
statistics_level 参数是oracle9.2开始引入的一个控制系统统计参数收集的一个开关.一共有三个值:basic,typical,all.支持alter session,alter system 动态修改.如果要用statspack或者AWR收集系统性能统计数据.那么这个参数的值必须为typical或all.通常all是一个全面收集,包括 OS以及sql执行路径方面的一些统计信息,除非遇见非常严重的性能问题或在一些特殊的性能挣断方面才会用到statistics_level=all, 平常statistics_level=typeical已经足够诊断99%的性能问题了.
alter system set statistics_level=basic;
alter system set statistics_level=typical;
alter system set statistics_level=all;
or
alter session set statistics_level=basic;
alter session set statistics_level=typical;
alter session set statistics_level=all;
statistics_level=basic的情况下,oracle关闭了所有性能数据的收集,也就是如果要关闭AWR或statspack收集,只要设置alter system set statistics_level=basic;就行了;statistics_level=typical的时候,除了plan_executetion_statistics和OS Statistics不能收集外,其他的都可以收集,如要要收集这个两项,必须设置statistics_level=all;如果当statistics_level=ALL,系统收集所有的统计信息.

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