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Which two statements are true about the use of the DYNAMIC_SAMPLING hint in a query?
A. It estimates selectivity better for the filters.
B. It is always used for flashback queries that contain the AS OF clause.
C. It cannot be used if there is a single-table predicate in the WHERE clause.
D. It cannot be used for processing SQL statements in parallel.
E. It can compensate for the lack of extended statistics to get accurate cardinality estimates for complex predicate expressions.
Correct Answer: DE
Explanation/Reference:
D:For parallel statements, the optimizer automatically decides whether to use dynamic sampling and which level to use.
The decision depends on the size of the tables and the complexity of the predicates. The optimizer expects parallel statements to be resource-intensive,so the additional overhead at compile time is worth it to ensure the best plan. The database ignores the For serially processed SQL statements, the dynamic sampling level depends on the value of the OPTIMIZER_DYNAMIC_SAMPLING parameter andis not triggered automatically by the optimizer. Serial statements are typically shortrunning, so that any overhead at compile timecould have a huge impact on their performance. the value is honored.
Reference: OracleDatabase Administrator’s Guide,About Oracle Database Resource Manager
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