The PLAN_TABLE is the key table for determining the access path for a query. The PLAN_TABLE provides the following critical information:
Indicates the joint method, or whether an additional sort step is required.
Indicates whether the access to is through a table space scan or through index access. If it is by index access, the specific type of index access is indicated.
Indicates the number of columns that are matched against the index if an index access is used.
Indicates that the access required can be served by accessing the index only, and avoiding any table access when a value of Y is in this column.
Indicates any sorts that may happen in support of a UNION, grouping, joint operation, and so on.
Indicates whether the prefetch can play a role in the access.
By manually running EXPLAIN and examining the PLAN-TABLE, you can retrieve the following information:
If you have additional EXPLAIN tables (for example, those created by Visual Explain or the Optimization Service Center), those tables are populated automatically. This is done by using those tools or by manually running EXPLAIN. If you do not have the remote access that is required from a PC to use the tools, you can also query those tables manually.
The tables provide detailed information about such entities as predicates stages, filter factors, eliminated partitions, parallel operations, detailed cost information, and so on.
Note: For more information about tables, see the DB2 Performance Monitoring and Tuning Guide (DB2 9).
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