IBM DB2 Optimization Expert, Version 2.1

Graphing the access plan for a query

You can generate a diagram of the current access plan for a query to find out how DB2® access data to process a query. This information is the same information that is in PLAN_TABLE, but it is presented in an easy-to-read, visual format.

Prerequisite: Before you can create an access plan graph:
  • The subsystem must be configured for tuning.
  • You must have authorization to issue the EXPLAIN statement for the query.

Also, consider specifying EXPLAIN options and environment parameters.

To graph the access plan for a query:
  1. If the Query page is open, select one of the following options in the EXPLAIN options menu:
    Use local EXPLAIN information
    Specifies use of the EXPLAIN information that is cached on your local machine. This option is available only when the EXPLAIN timestamp field has a value, which means that the EXPLAIN information for this query exists in your local cache. If this information exists but is not up to date, consider selecting one of the other two options.
    Use subsystem EXPLAIN information
    Specifies to collect existing EXPLAIN information for this query from the EXPLAIN tables on the selected subsystem. If this information exists but is not up to date, consider selecting the Run EXPLAIN again option.
    Run EXPLAIN again
    Specifies to issue the EXPLAIN statement for the specified query and collect the resulting information from the EXPLAIN tables on the DB2 for z/OS® subsystem.
  2. Click Tools > Graph Access Plan. If the View Queries page is open, select Action > Access Plan Graph. The access plan graph is displayed.

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