SQL Optimizer for DB2 LUW 4.3.1 - Installation Guide

Optimization Details

The Rewrite Details dialog is optional and can be displayed after the SQL Rewrite process completes. This dialog displays the number of semantically equivalent SQL statements investigated and the number of valid SQL alternatives produced. The dialog displays the following:

• Time calculations for the rewrite process.

• Number of semantically equivalent SQL statements investigated.

• Number of alternative access plans produced.

• How many rewrites were eliminated because they have identical access plans or DB2 LUW costs.

• Warning message if the Syntax Transformation Quota, Total SQL Options Quota, or Table Join Permutation Quota is reached.

Note: Use the Optimization (2) page on the SQL Rewrite tab in Options to define whether to eliminate alternative SQL statements when they have identical access plans or identical DB2 LUW costs. Eliminating the SQL based on identical access plan is more accurate but it can take longer to determine.

The Rewrite Details dialog is shown every time the rewrite process completes. To disable this window, clear the Show details on next optimization option in the dialog.

To view the Rewrite Details dialog at anytime

Select View | Show Optimization Details in the SQL Optimizer window.

If no alternatives are available, the Generate Indexes button is provided to start the Index Expert process of determining virtual index sets that might improve performance. See Generate Index-Set Alternatives for more information.