Bitmap Index
A bitmap index maintains one bitmap per key value (each bit corresponds to a row), suited to ad-hoc analytical queries on low-cardinality columns.
Purpose
To optimize queries on low-cardinality columns (gender, status) and understand the compression and Boolean-operation advantages.
Mechanism
The bitmap for value V has bit i set if row i holds V. Queries filter quickly with bitmap AND/OR/NOT. Compressed bitmaps (RLE, WAH) reduce space. Great for OLAP star queries; unsuitable for high-cardinality or frequently updated columns.
Use cases
- OLAP query optimization
- Low-cardinality column indexing
- Star queries