The optimizer must determine how to access the data your SQL statements require. You formulate your statement and the optimizer, during a hard parse, will figure out which operations should provide the data in the most effective way possible. Using statistics as the primary guide, the optimizer will compute the cost of the possible alternatives to first access data and then join multiple tables to get the final result set. The more you understand about the different access and join methods the optimizer will consider, the more likely you will be to formulate your SQL to help the optimizer make the best choices. And, when the operation chosen by the optimizer doesn’t provide the performance you need, you can more accurately determine which operations would be more suited to produce the response times you want.
KeywordsHash Table Nest Loop Execution Plan Cluster Factor Index Block
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