Home » Oracle » 1z0-117 » Which three factors does the estimator depend on for overall cost estimation of a given execution plan?
Which three factors does the estimator depend on for overall cost estimation of a given execution plan?
A. Cardinality
B. Sort area size
C. OPTIMIZER_FEATURE_ENABLE parameter
D. NOT NULL_FEATURE_ENABLE parameter
E. NOT NULL constraint on a unique key column
F. Library cache size
G. The units of work such as disk input/output, CPU usage, and memory used in an operation
Correct Answer: ACG
Explanation/Reference:
C:OPTIMIZER_FEATURES_ENABLE acts as an umbrella parameter for enabling a series of optimizer features based on an Oracle release number.
Note:The estimator determines the overall cost of a given execution plan. The estimator generates three different types of measures to achieve this goal:
*Selectivity
This measure represents a fraction of rows from a row set. The selectivity is tied to a query predicate, such as last_name=’Smith’, or a combination of predicates.
*Cardinality
This measure represents the number of rows in a row set.
1,
*Cost
This measure represents units of work or resource used. The query optimizer uses disk I/O, CPU usage, and memory usage as units of work.
If statistics are available, then the estimator uses them to compute the measures. The statistics improve the degree of accuracy of the measures.
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