Viewing Actual Versus Estimated Cardinalities

Teradata Visual Explain User Guide

Teradata Tools and Utilities
Visual Explain
User Guide
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.
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.

  1. Click .

    The Actual Versus Estimated Cardinality window opens.

    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.
    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.

    Stepwise Cardinality Distribution Graph