Welcome to Visual Explain.
Visual Explain lets you view the access plan
for explained SQL statements as a graph. You can use the information
available from the graph to tune your SQL queries for better
performance.
An access plan graph shows details of:
- Tables (and their associated columns) and indexes
- Operators (such as table scans, sorts, and joins)
- Table spaces and functions.
You can also use Visual Explain to:
- View the statistics that were used at the time of optimization. You
can then compare these statistics to the current catalog statistics to help
you determine whether rebinding the package might improve performance.
- Determine whether or not an index was used to access a table. If an
index was not used, Visual Explain can help you determine which columns might
benefit from being indexed.
- View the effects of performing various tuning techniques by comparing the
before and after versions of the access plan graph for a query.
- Obtain information about each operation in the access plan, including the
total estimated cost and number of rows retrieved (cardinality).
The following sections provide an overview of how to use Visual Explain to
analyze SQL statements. For detailed information,
see
the DB2 books that are referenced throughout these sections.
- Producing an access plan graph.
- Creating an explain snapshot.
- Displaying and using an access plan
graph.
- Improving the access plan.
- Performing SQL tuning activities.
| Note: |
- The process of tuning queries is iterative, and the tasks described
throughout the above sections can be repeated as required.
- You can also use the Command Center to
interactively create access plans.
- You can use the Control Center to perform database
administration tasks.
- To see a list of Visual Explain tasks, return to the Contents and review
the tasks under Analyzing SQL statements using Visual
Explain. These tasks include instructions on how to open to each
of the Visual Explain windows.
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