When to create Bitmap Indexes

• When a table has millions of rows and the key columns have low cardinality—that is, there are very few distinct values for the column. For example, bitmap indexes may be preferable to B-tree indexes for the gender and marital status columns of a table containing passport records
• When queries often use a combination of multiple WHERE conditions involving the OR operator
• When there is read-only or low update activity on the key columns