Query Optimizers
The role of the query optimizer is to find the most efficient way of retrieving and processing the data necessary to satisfy a query. The approach decided on by the optimizer is variously called a query plan (QP), a query execution plan (QEP), or an explain plan. The effectiveness of the query plan chosen by the optimizer is important for Online Transaction Processing (OLTP) queries, which are typically lightweight, and crucial for Decision Support (DSS) queries, which can consume vast amounts of CPU and I/O resources.
An analogy might help illustrate the issues. You can get from California to New York by plane, bus, car, sea, bicycle, or on foot. If you want the fastest method you would fly, although that isn’t likely to be ...
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