Expert Indexing in Oracle Database 11g: Maximum Performance for Your Database

Understanding Bitmap Join Indexes

Bitmap join indexes, like normal bitmap indexes, are useful in data warehouse applications, specifically with the star schema. One of the key benefits of a bitmap join index is implied in the name of the index: the join. The basic premise of a bitmap join index is as follows: when creating a bitmap join index, which is a join of indexed values between two tables, the join results are stored within the index itself. By doing the join upfront and storing the results, it saves you from having to scan the indexes to get join values between the two tables.

Within a star schema, the base elements for the bitmap join index are the large fact table and the dimension table. In a normal star schema, there are foreign keys ...