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  Oracle Tips by Burleson

Monitoring Bitmap Join Indexes

As noted earlier, bitmap join indexes were introduced in Oracle. If the JOIN_INDEX column in the DBA_INDEXES is set to YES, then the index is a bitmap join index, meaning that a join to the DBA_JOIN_IND_COLUMNS view will produce the data on the tables and columns that are linked through the bitmap join index. You will need to join against the INDEX_OWNER and INDEX_NAME columns.      

My testing, however, revealed an apparent flaw in the DBA_JOIN_IND_COLUMNS view--at least based on how I believe it should work. That view seems to have the same number of columns as the DBA_IND_COLUMNS view. In addition, it contains only one row per bitmap join index, when it should show one row for each of the two tables involved in the bitmap join. In tests where I created a bitmap join between two tables with different column names, only one row was displayed. Where the actual information about the second table is stored, if it is, is not clear. Until this is resolved I suggest using naming conventions to clarify the required table-to-table relationship.

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