Compare Actual to Estimated Cost
When comparing actual to estimated cost, use Teradata Visual Explain to load the actual cost information from the DBQL for the most recently logged execution of the query.
Note: This feature is available only for plans captured using QCD.
To compare actual to estimated cost
Load an execution plan before viewing cost. For more information, see “Loading and Viewing an Execution Plan” on page 149.
1 Click .
The Actual Versus Estimated Cost window opens.
Figure 57: Actual Versus Estimated Cost for Query ID
|
Column Name |
Description |
|
Step |
Step number in the query plan |
|
CPU Time |
CPU the step uses |
|
IO Count |
I/O the step uses |
|
StepStart Time |
Timestamp, to the nearest microsecond, when the step was sent to the AMP |
|
StepStop Time |
Timestamp, to the nearest microsecond, when the step returned from the AMP |
|
Elapsed Time |
Difference between StepStop Time and StepStart Time |
|
CPU Cost |
Estimated CPU time required to execute the step |
|
IO Cost |
Estimated I/O time required to execute the step |
|
Network Cost |
Estimated network time required to execute the step |
|
Total Cost |
Total estimated time required to execute the step |
Note: If the query is not present in the DBQL, only the estimated cost appears. If the query is found, the actual and estimated stepwise costs appear.
2 [Optional] In the Actual vs. Estimated Cost window, double-click the column headings to change the sort order.
For example, double‑click the CPU Cost column heading to list the steps with the highest cost estimates first.
3 To view the graphical layout of the stepwise costs, click View Graph in the table.
Figure 58: Stepwise Cost Distribution Graph for Query ID