SQL Optimizer for DB2 LUW 4.3.1 - User Guide

What Function Should l Use to Retrieve the Run Time?

The SQL Optimizer provides two different measurements of performance; the run time for retrieving all records and the run time for retrieving the first n records. Both measurements give you an indication on the fastest running SQL statement—but with two different aims. You must understand the use of the SQL statement in the application. Generally, if the SQL statement is used for reports, then you should use the Run for All Record or Batch Run with Run Time Mode set to All Records. If the SQL statement is used for online query, then use the Run for First Record or Batch Run with Run Time Mode set to First n Record.

Note: If the aim of the SQL statement is unknown, then use All Records as a performance indication.

Unsatisfactory Performance Results

After optimization and execution testing, you may discover that the performance of the optimized SQL statements is still not satisfactory. To remedy this, first check that the searching quota has not been reached in the Optimization Details window. If it has, then you should increase the intelligence level or optimization options in the Options window and optimize again to ensure all transformed SQL statements are given. Rerun the SQL statement optimization after the review.

You can also review the access plan of the optimized SQL statement to check if there should be any alterations to the database structure such as adding a new index. The Index Expert module is used to generate alternative Index Sets for a SQL statement.

SQL Functions

The following SQL Functions are available in the SQL Optimizer window to retrieve the access plan, the run time, result set and to convert parameter markers:

Show Plan

Run Result (SQL alternatives only)

Run for First Record

Record for All Records

Convert Parameter Markers

Test for Scalability

SQL Optimizer Functions

Below is a list of available functions within the SQL Optimizer window.

These functions are available only for the original SQL statement <Edit SQL> when displayed in the editable SQL Text window.

These functions are available for original SQL and its alternatives.

These functions are available only after the original SQL statement has been rewritten or virtual indexes have been generated.