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