55: 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 AutomaticWorkload 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.
Correct Answers: C
Explanation:
设置 STATISTICS_LEVEL = BASIC 会禁用以下oracle 的功能特性
Automatic Workload Repository (AWR) Snapshots
Automatic Database Diagnostic Monitor (ADDM)
All server-generated alerts
Automatic SGA Memory Management （ASMM）和自动内存管理
Automatic optimizer statistics collection
Object level statistics
End to End Application Tracing (V$CLIENT_STATS)
Database time distribution statistics (V$SESS_TIME_MODEL and V$SYS_TIME_MODEL)
Service level statistics
Buffer cache advisory
MTTR advisory
Shared pool sizing advisory
Segment level statistics
PGA Target advisory
Timed statistics
Monitoring of statistics
参考《References》中STATISTICS_LEVEL初始化参数
STATISTICS_LEVEL = BASIC会禁用许多重要的统计信息的收集：
1. AWR快照
2. ADDM (Automatic Database Diagnostic Monitor) 是植入Oracle数据库的一个自诊断引擎.ADDM 通过检查和分析AWR获取的数据来判断Oracle数据库中可能的问题.
3. 所有server-generated预警
4. 自动SGA内存管理
5. 对象层次的统计信息
6. 端到端的应用程序跟踪（v$CLIENT_STATS)
7. 数据库时间分布统计（V$SESS_TIME_MODEL和V$SYS_TIME_MODEL）
8. 服务层次的统计
9. Buffer cache advisor
10. MTTR advisor 顾问 MTTR（mean time to restoration， 平均恢复前时间），源自于IEC 61508中的平均维护时间（mean time to repair），目的是为了清楚界定术语中的时间的概念，MTTR是随机变量恢复时间得期望值
11. Shared Pool size advisor
12. 段层次的统计信息
13. PGA Target advisor
14. Timed statistics
15. 统计的监控