Starting Visual Explain

You can start Visual Explain from any of the following windows in iSeries Navigator:

• Enter an SQL statement in the Run SQL Scripts window. Select the statement and choose Explain from the context menu, or select Run and Explain from the Visual Explain menu.
• Expand the list of available SQL Performance Monitors. Right-click a detailed SQL Performance Monitor and choose the Show Statements option. Select filtering information and select the statement in the List of Statements window. Click Run Visual Explain. You can also start an SQL Performance Monitor from Run SQL Scripts. Select Start SQL Performance monitor from the Monitor menu.
• Start the Current SQL for a Job function by right-clicking Databases and select Current SQL for a Job. Select a job from the list and click SQL Statement. When the SQL is displayed in the lower pane, you can start Visual Explain by clicking Run Visual Explain.
• Right-click SQL Plan Cache and select Show Statements. Select filtering information and select the statement in the List of Statements window. Click Run Visual Explain.
• Expand the list of available SQL Plan Cache Snapshots. Right-click a snapshot and select Show Statements. Select filtering information and select the statement in the List of Statements window. Click Run Visual Explain.

You have three options when running Visual Explain from Run SQL Scripts.

Visual Explain only

This option allows you to explain the query without actually running it. The data displayed represents the query optimizer's estimates.

Note: When using the Explain only option of Visual Explain from Run SQL Scripts in iSeries Navigator, some queries receive an error code 93 stating that they are too complex for displaying in Visual Explain. You can circumvent this by selecting the "Run and Explain" option.

Run and Explain

If you select Run and Explain, the query is run by the system before the diagram is displayed. This option may take a significant amount of time, but the information displays is more complete and accurate.

Explain while running

For long running queries, you can choose to start Visual Explain while the query is running. By refreshing the Visual Explain diagram, you can view the progress of the query.

In addition, a database monitor table that was not created as a result of using iSeries Navigator can be explained through iSeries Navigator. First you must import the database monitor table into iSeries Navigator. To do this, right-click the SQL Performance Monitors and choose the Import option. Specify a name for the performance monitor (name it will be known by within iSeries Navigator) and the qualified name of the database monitor table. Be sure to select Detailed as the type of monitor. Detailed represents the file-based (STRDBMON) monitor while Summary represents the memory-resident monitor (which is not supported by Visual Explain). Once the monitor has been imported, follow the steps to start Visual Explain from within iSeries Navigator.

You can save your Visual Explain information as an SQL Performance monitor, which can be useful if you started the query from Run SQL Scripts and want to save the information for later comparison. Select Save as Performance monitor from the File menu.