![]() External statistics - Oracle will sample the CPU cost and I/O cost during statistics collection and use this information to determine the optimal execution plan, based on optimizer_mode.Foreign key columns - For n-way table joins, the CBO needs to determine the optimal table join order and knowing the cardinality of the intermediate results sets is critical. ![]() Heavily skewed columns - This helps the CBO properly choose between an index range scan and a full table scan.Critical columns - Those columns that are regularly-referenced in SQL statements that are:.Object statistics - Statistics for all tables, partitions, IOTs, etc should be sampled with a deep and statistically valid sample size. ![]() If we provide Oracle with good statistics about the schema the CBO will almost always generate an optimal execution plan. OPTIMIZER_MODE can have the following values:
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