DB2 UDB for z/OS Version 8 Performance Topics - IBM Redbooks

You can also use Visual Explain:
► To generate customized reports on explicable statements
► To view subsystem parameters
► To view data from the plan table, statement table, and function table
► To list SQL statements stored in the catalog (SYSSTMT and SYSPACKSTMT)
Note: All these functions can be executed with a click in the corresponding icon in the
Visual Explain icon bar.
You can link to these suggestions directly from the graph. You can also link from the graph to
additional statistics and descriptions for each object or operation that is used in the access
plan.
Each graph can display multiple query blocks, so that you can view the entire access plan in
one graph. In previous versions of Visual Explain, each graph displayed only one query block.
In this version, you still have the option to view only one query block at a time. You can use
Visual Explain to catalog and uncatalog databases on your local machine, to list DSNZPARM
parameters by installation field name, alphabetically by parameter name, or by installation
panel name. You maintain Visual Explain by deleting old records from the EXPLAIN tables.
With DB2 V8 Visual Explain, you can save the access path graph for later use, because
Visual Explain uses XML to store the graph information. Every time that you EXPLAIN a
statement, the access path graph is displayed on the Access Plan page of the Tune SQL
notebook. On this page, select File → Save XML File to save the XML file to your local work
station. To retrieve the graph, select File → Open XML File. You can also send the XML file to
other people. If they have DB2 Visual Explain installed, they can also see the graph.
Note: Visual Explain has enhanced capabilities related to qualified rows estimates. It
provides a wealth of predicate information, more partition scan information, and parallelism
details.
Visual Explain uses some sample stored procedures:
► DSNWZP
This stored procedure is required to support the Browse Subsystems Parameters function.
The stored procedure is also used by Service SQL for collection and transmission of
subsystem parameter settings to IBM service.
► DSN8EXP
This stored procedure (see also APARs PQ90022 and PQ93821) supports the EXPLAIN with
stored procedure option. The purpose of EXPLAIN with stored procedure is to allow you to
EXPLAIN SQL against objects against which you do not have the authority to execute
queries. For example, a developer may have responsibilities for SQL performance on a payroll
application, but may not have SELECT, INSERT, UPDATE, and DELETE access to the object.
The developer can use the stored procedure to execute the Explain against the object. The
developer does not need access to the objects, but the authority to execute the stored
procedure.
► DSNUTILS
Statistics Advisor generates RUNSTATS statements. These RUNSTATS statements can be
executed dynamically if you have a license to execute RUNSTATS, the DSNUTILS stored
procedure is installed, and you have appropriate authority to execute the RUNSTATS
Chapter 3. SQL performance 111