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Exam 1z0-062 topic 1 question 59 discussion

Actual exam question from Oracle's 1z0-062
Question #: 59
Topic #: 1
[All 1z0-062 Questions]

Examine the parameter for your database instance:

You generated the execution plan for the following query in the plan table and noticed that the nested loop join was done. After actual execution of the query, you notice that the hash join was done in the execution plan:

Identify the reason why the optimizer chose different execution plans.

  • A. The optimizer used a dynamic plan for the query.
  • B. The optimizer chose different plans because automatic dynamic sampling was enabled.
  • C. The optimizer used re-optimization cardinality feedback for the query.
  • D. The optimizer chose different plan because extended statistics were created for the columns used.
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Suggested Answer: A 🗳️
by Mamlouk_Med at Feb. 26, 2019, 7:34 a.m.

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Ray520
2 years, 5 months ago
it's A. Optimizer_dynamiz_sampling value is 2 (default) which means it uses dynamic statistics if at least one table has no statistics.
upvoted 1 times
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Oracle2020
2 years, 9 months ago
I Think B Explanation/Reference: Explanation: * optimizer_dynamic_sampling OPTIMIZER_DYNAMIC_SAMPLING controls both when the database gathers dynamic statistics, and the size of the sample that the optimizer uses to gather the statistics. Range of values0 to 11
upvoted 1 times
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TuxBingo
4 years, 4 months ago
The correct answer is A, Why? Oracle Documentation: https://docs.oracle.com/database/121/TGSQL/tgsql_astat.htm#TGSQL451 -- Table 13-1 Dynamic Statistics Levels -- 2 Use dynamic statistics if at least one table in the statement has no statistics. This is the default value, so for that reason: The optimizer used a dynamic plan for the query.
upvoted 4 times
jackymak
2 years, 7 months ago
Thanks, It should be A. If optimizer_dynamic_sampling values = 11 then C will be right.
upvoted 1 times
jackymak
2 years, 7 months ago
***I mean "then B will be right"
upvoted 1 times
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Mamlouk_Med
5 years, 9 months ago
I Think B
upvoted 2 times
5kong
5 years, 1 month ago
why? automatic dynamic sampling was enabled ?? the answer is A
upvoted 6 times
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