第101題-OCP認證062考試題庫2019最新考題解析
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我要咨詢2018年的時候，OCP 11g考試題庫大更新，052 053出現了很多新題，
2019年，11g即將�？嫉那捌�，Oracle又出現了一次大變動，12c出現了很多新題，比如062 063題庫大更新
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QUESTION 101
Examine the parameters for your database instance:
optimizer_adaptive_reporting_only boolean FALSE
optimizer_adaptive_statistics boolean FALSE
optimizer_capture_sql_plan_baselines boolean FALSE
optimizer_dynamic_sampling integer 2
optimizer_features_enable string 12.1.0.1
Which three statements are true about the process of automatic optimization by using cardinality feedback?
A. The optimizer automatically changes a plan during subsequent execution of a SQL statement if there is a huge difference in optimizer estimates and execution statistics.
B. The optimizer can re optimize a query only once using cardinality feedback.
C. The optimizer enables monitoring for cardinality feedback after t he first execution of a query.
D. The optimizer does not monitor cardinality feedback if dynamic sampling and multicolumn statistics are enabled.
E. After the optimizer identifies a query as a re-optimization candidate, statistics collected by the collectors are submitted to the optimizer.
Correct Answer: ACD
Section: (none)
( 解析： 在下列情況 CBO 可能無法估算出準確的 Cardinality，Oracle 會啟用 CFB 功能：
?沒有收集表的統計信息，并且 dynamic sampling 也沒有開啟;
? 一個表的查詢條件涉及多列，但卻沒有收集擴展的統計信息(extended statistics)
? 查詢條件復雜(比如條件有函數)
