Viewing Actual Versus Estimated Cardinalities - Visual Explain

Teradata Visual Explain User Guide

Product
Visual Explain
Release Number
15.10
Language
English (United States)
Last Update
2018-10-07
dita:id
B035-2504
lifecycle
previous
Product Category
Teradata Tools and Utilities

When comparing actual cardinalities to estimated cardinalities, Teradata Visual Explain loads the actual cardinality information from the DBQL for the most recently logged execution of the query.

Note: This feature is available only for plans captured using QCD.

Load an execution plan before viewing cardinalities. For more information, see “Loading and Viewing an Execution Plan” on page 145.

1 Click .

The Actual Versus Estimated Cardinality window opens.

Note: If the query is not present in the DBQL, only the estimated cardinality appears. If the query is found, the actual and estimated cardinalities appear.

Figure 54: Actual Versus Estimated Cardinality
 

Column Name

Description

Step Number

Step number in the query plan.

Spool Name

Name of the spool in the query plan.

Actual Cardinality

Actual number of rows in the spool.

Estimated Cardinality

Estimated number of rows in the spool.

Cardinality Difference

Difference between actual versus estimated cardinality.

2 [Optional] Double-click the column headings to change the sort order.

For example, double‑click the Estimated Cardinality column heading to list the steps with the highest cardinality estimates first.

3 To view the graphical layout of the stepwise cardinalities, click View Graph.

The Stepwise Cardinality Distribution Graph appears and displays the actual cardinality compared to the estimated cardinality in a graph format.

Figure 55: Stepwise Cardinality Distribution Graph