Chapter 21. The Optimizer

In This Chapter

• Physical Data Independence

• How the Optimizer Works

• Filter Factors

• Screening

• Access Path Strategies

• Other Operations Performed by the Optimizer

The optimizer is the heart and soul of DB2. Before any SQL statement is run, the optimizer analyzes the SQL and determines the most efficient access path available for satisfying the statement. It accomplishes this by parsing the SQL statement to determine which tables and columns must be accessed. It then queries statistics stored in the DB2 Catalog to determine the best method of accomplishing the tasks necessary to satisfy the SQL request.

Statistics used by the optimizer include information about the current status of the tables, indexes, columns, ...

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