Introduction to Bitmap Indexes

Introduction to Bitmap Indexes

To alleviate confusion, I will refer to bit-indexing and bit mapped indexing as a bitmap index.  Through my research I have seen these terms used interchangeably to define the same concept – bitmap indexes.

What is a bitmap index and how do they work?

Bitmap indexes are a mechanism, largely employed by Oracle databases, to increase search performance on large data sets.  Bitmap indexes are most effective when applied to columns that exhibit low cardinality.  In this case, cardinality represents the amount of unique values that a column may contain.  For example, a column called “Active” on a user account table would likely only contain two values: true or false (or active and disabled).  Regardless of the total number of tuples,  the values contained in this column is only two possible values.  This column exhibits low cardinality.  A column that exhibits high cardinality benefit less from creating an index on them and become candidates for a primary key – that is if each tuple contains a unique value. Continue reading