11.6. Cost Estimation in Query Optimization
The main aim of query optimization is to choose the most efficient way of implementing the relational algebra operations at the lowest possible cost. Therefore, the query optimizer should not depend solely on heuristics rules, but, it should also estimate the cost of executing the different strategies and find out the strategy with the minimum cost estimate. The method of optimising the query by choosing a strategy those results in minimum cost is called cost-based query optimization. The cost-based query optimization uses formulae that estimate the costs for a number of options and selects the one with lowest cost and most efficient to execute. The cost functions used in query optimization are estimates ...
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