What-if Analysis Process - Teradata Index Wizard

The What-if analysis process starts when you click the Analyze button. The DDL statements in the grid are simulated on the system. Each DDL statement submitted is indicated in the status bar. If COLLECT STATISTICS statements are present in the DDL, a warning message appears.

When you click OK, the statistics collected for the tables in the workload are displayed (the View/Modify Statistics Samples option must be set to “yes”). You can view the statistics and modify them. These statistics will be used during plan generation.

The following table describes the statistics after they are generated.

Table 25: Analysis Statistics Dialog Box Descriptions 

Option	Description
Database objects	Displays the hierarchy of the objects where the statistics exist.
Database Name	Displays the database where the table is present.
Table Name	Displays the table where the statistics are collected.
Interval Type	Selects the interval types to be displayed. The values are All, High-biased, and Equal.
Column Name	Displays the column name where the statistics are collected.
Number of Rows	Displays the number of rows in the table.
Number of Nulls	Displays the number of null values.
Number of Intervals	Displays the number of intervals of statistics collected.
Number of Unique	Displays the number of unique values for the column where the statistics are collected.
Version	Displays the version.
Time Stamp	Adds a time stamp.
Minimum Value	Displays the minimum value for interval 0.
Mode Value	Displays the mode value of interval 0.
Mode Frequency	Displays the mode frequency of interval 0.

The workload statements are submitted to the server and the new plans are captured. During this phase, if the statistics were modified using the above option, the Optimizer uses the modified statistics. Otherwise, it uses the collected statistics while generating the plans. Additionally, the status bar displays the statement that is currently being processed.

If you do not perform an abort, the new execution costs for the statements in the workload are obtained. The dialog box shows the cost difference in percentage with and without the simulated indexes and statistics, and the overall improvement of the performance. You can compare these statements using Teradata Visual Explain. Select the plans to be compared and click Compare.