oracle ocp 052-153

最新推荐文章于 2026-01-06 22:02:48 发布

转载最新推荐文章于 2026-01-06 22:02:48 发布 · 87 阅读

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QUESTION 153
In your database instance, the STATISTICS_LEVEL initialization parameter is set to BASIC.
What is the impact of this setting?
A. Optimizer statistics are collected automatically.
B. Only timed operating system (OS) statistics and plan execution statistics are collected.
C. The snapshots for the Automatic Workload Repository (AWR) are not generated automatically.
D. Snapshots cannot be collected manually by using the DBMS_WORKLOAD_REPOSITORY package.
E. The Oracle server dynamically generates the necessary statistics on tables as part of query optimization

解析：
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.
example: seting statistics_level

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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