In which of these cases should statistics be run on database schema objects? (Choose two.)
A . OPTIMIZER_MODE=COST
B. OPTIMIZER_MODE=CHOOSE
C . The RBO is used exclusively by setting OPTIMIZER_MODE=TRUE.
D. OPTIMIZER_MODE=ALL_ROWS
E . OPTIMIZER_MODE=RULE
Explanation:
Answer B and D: TRUE and COST are not valid OPTIMIZER_MODE settings. When RULE is specified, statistics are not used. ALL_ROWS and CHOOSE are both CBO settings; that is, ALL_ROWS indicates to the CBO that it should optimize for throughput, and CHOOSE indicates to use the CBO if statistics are available on any table in the SQL statement. If any table in the SQL statement has statistics on it, then performance is better under the CHOOSE option; however, performance will be best if all the tables have statistics on them.
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