10.3 Physical Query Optimization
The next step in optimization is for the strategy selector to choose an execution plan. To develop an execution plan, the strategy selector must consider the various ways each of the operations in the query tree could be executed. It “prices” each method by considering the costs of the processes involved.
10.3.1 Cost Factors
The cost of executing a query is determined by the cost of reading files, the processing costs once data is in main memory, the cost of writing and storing any intermediate results, the communication costs, and the cost of writing the final results to storage. Of these, the most significant factor is the number of data accesses—the read and write costs. In calculating these costs, the DBMS ...
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