Bitmap Indices¶
Bitmap Index¶
A bitmap index is a special kind of index designed for querying on multiple keys efficiently.
- Records are assumed to be in numerically sequential form.
- Given a number \(n\) it must be easy to retrieve the \(n\)'th record, especially if records are of fixed size
- It's great for records that take on a relatively small number of distinct values
Storage Mechanism¶
A bitmap index is basically an inverted hash table on the row
| income_level |
|---|
| L1 |
| L2 |
| L1 |
| L4 |
| L3 |
becomes
L1 - 10100
L2 - 01000
L3 - 00001
L4 - 00010
L5 - 00000
These can be great for applying boolean algebra on (e.g., select all people who have income level L1 or L2, etc.)