Bitmap Index¶
Bitmap indices use bit arrays to represent the presence or absence of values, providing extremely fast query performance for low-cardinality columns.
Index Details¶
Storage Layout¶
The bitmap index consists of a single file bitmap_page_lookup.lance that stores the mapping from values to their bitmaps.
File Schema¶
| Column | Type | Nullable | Description |
|---|---|---|---|
keys |
{DataType} | true | The unique value from the indexed column |
bitmaps |
Binary | true | Serialized RowIdTreeMap containing row IDs where this value appears |
Accelerated Queries¶
| Query Type | Description | Operation |
|---|---|---|
| Equals | column = value |
Returns the bitmap for the specific value |
| Range | column BETWEEN a AND b |
Unions all bitmaps for values in the range |
| IsIn | column IN (v1, v2, ...) |
Unions bitmaps for all specified values |
| IsNull | column IS NULL |
Returns the pre-computed null bitmap |