Skip to main content
Scalar indexes organize data by scalar attributes (e.g., numbers, categories) and enable fast filtering of vector data. They accelerate retrieval of scalar data associated with vectors, thus enhancing query performance. LanceDB supports three types of scalar indexes:
  • BTREE: Stores column data in sorted order for binary search. Best for columns with many unique values.
  • BITMAP: Uses bitmaps to track value presence. Ideal for columns with few unique values (e.g., categories, tags).
  • LABEL_LIST: Special index for List<T> columns supporting array_contains_all and array_contains_any queries.

​
Choosing the Right Index Type

Data TypeFilterIndex Type
Numeric, String, Temporal<, =, >, in, between, is nullBTREE
Boolean, numbers or strings with fewer than 1,000 unique values<, =, >, in, between, is nullBITMAP
List of low cardinality of numbers or stringsarray_has_any, array_has_allLABEL_LIST

​
Scalar Index Operations

​
1. Build the Index

You can create multiple scalar indexes within a table. By default, the index will be BTREE, but you can always configure another type like BITMAP
If you are using Cloud or Enterprise, the create_scalar_index API returns immediately, but the building of the scalar index is asynchronous. To wait until all data is fully indexed, you can specify the wait_timeout parameter on create_scalar_index() or call wait_for_index() on the table.

​
2. Check Index Status

​
3. Update the Index

Updating the table data (adding, deleting, or modifying records) requires that you also update the scalar index. This can be done by calling optimize, which will trigger an update to the existing scalar index.
New data added after creating the scalar index will still appear in search results if optimize is not used, but with increased latency due to a flat search on the unindexed portion. LanceDB Cloud automates the optimize process, minimizing the impact on search speed.

​
4. Run Indexed Searches

The following scan will be faster if the column book_id has a scalar index: Scalar indexes can also speed up scans containing a vector search or full text search, and a prefilter:

​
Advanced: Index UUID Columns

LanceDB supports scalar indexes on UUID columns (stored as FixedSizeBinary(16)), enabling efficient lookups and filtering on UUID-based primary keys.
To use FixedSizeBinary, ensure you have:

​
1. Define UUID Type

​
2. Generate UUID Data

​
3. Create Table with UUID Column

​
4. Create and Wait for the Index

​
5. Perform Operations with the UUID Index