Chapter 15 DBMS-Specific Features

Automatically creating bitmap join indexes through rebuilding

You can automatically generate a bitmap join index for each fact table and the dimension tables that it references. Each generated bitmap join index consists of the references that link a fact table to all the dimension tables located on a single axis proceeding from the fact table.

A reference between two fact tables does not generate any bitmap join index. A bitmap join index is constrained and can only be defined for tables that are organized in a connected tree.

To rebuild bitmap join indexes for all references linked to a fact table:

1. Select Tools→Rebuild Objects→Rebuild Join Indexes to open the Rebuild Join Indexes dialog box, and select one of the following modes:
   
   
   • Delete and Rebuild - all existing indexes are deleted before join index rebuild.
   • Preserve - preserves all existing join indexes in the PDM
     
2. Click the Selection tab, select one or more fact tables in the list, and then click OK.
   
   A confirmation box asks if you want to continue.
3. Click Yes to generate a bitmap join index for each fact table.
   
   
      Displaying automatically generated bitmap join indexes
   Automatically generated bitmap join indexes appear in the list of join indexes. To display the list, select Model→Join Indexes.
   
   

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