Documentation Index

Fetch the complete documentation index at: https://docs.turso.tech/llms.txt Use this file to discover all available pages before exploring further.

Vector Similarity Search is built into Turso and libSQL Server as a native feature.

Turso and libSQL enable vector search capability without an extension.

• Create a table with one or more vector columns (e.g. FLOAT32)
• Provide vector values in binary format or convert text representation to binary using the appropriate conversion function (e.g. vector32(...))
• Calculate vector similarity between vectors in the table or from the query itself using dedicated vector functions (e.g. vector_distance_cos)
• Create a special vector index to speed up nearest neighbors queries (use the libsql_vector_idx(column) expression in the CREATE INDEX statement to create vector index)
• Query the index with the special vector_top_k(idx_name, q_vector, k) table-valued function

LibSQL uses the native SQLite BLOB storage class for vector columns. To align with SQLite affinity rules, all type names have two alternatives: one that is easy to type and another with a _BLOB suffix that is consistent with affinity rules.

We suggest library authors use type names with the `_BLOB` suffix to make results more generic and universal. For regular applications, developers can choose either alternative, as the type name only serves as a **hint** for SQLite and external extensions. As LibSQL does not introduce a new storage class, all metadata about vectors is also encoded in the `BLOB` itself. This comes at the cost of a few bytes per row but greatly simplifies the design of the feature.

The table below lists six vector types currently supported by LibSQL. Types are listed from more precise and storage-heavy to more compact but less precise alternatives (the number of dimensions in vector $D$ is used to estimate storage requirements for a single vector).

Type name	Storage (bytes)	Description
FLOAT64 | F64_BLOB	$8D + 1$	Implementation of IEEE 754 double precision format for 64-bit floating point numbers
FLOAT32 | F32_BLOB	$4D$	Implementation of IEEE 754 single precision format for 32-bit floating point numbers
FLOAT16 | F16_BLOB	$2D + 1$	Implementation of IEEE 754-2008 half precision format for 16-bit floating point numbers
FLOATB16 | FB16_BLOB	$2D + 1$	Implementation of bfloat16 format for 16-bit floating point numbers
FLOAT8 | F8_BLOB	$D + 14$	LibSQL specific implementation which compresses each vector component to single u8 byte b and reconstruct value from it using simple transformation: $\texttt{shift} + \texttt{alpha} \cdot b$
FLOAT1BIT | F1BIT_BLOB	$\lceil \frac{D}{8} \rceil + 3$	LibSQL-specific implementation which compresses each vector component down to 1-bit and packs multiple components into a single machine word, achieving a very compact representation

For most applications, the `FLOAT32` type should be a good starting point, but you may want to explore more compact options if your table has a large number of rows with vectors. While `FLOAT16` and `FLOATB16` use the same amount of storage, they provide different trade-offs between speed and accuracy. Generally, operations over `bfloat16` are faster but come at the expense of lower precision.

To work with vectors, LibSQL provides several functions that operate in the vector domain. Each function understands vectors in binary format aligned with the six types described above or in text format as a single JSON array of numbers.

Currently, LibSQL supports the following functions:

Function name	Description
vector64 | vector32 | vector16 | vectorb16 | vector8 | vector1bit	Conversion function which accepts a valid vector and converts it to the corresponding target type
vector	Alias for vector32 conversion function
vector_extract	Extraction function which accepts valid vector and return its text representation
vector_distance_cos	Cosine distance (1 - cosine similarity) function which operates over vector of same type with same dimensionality
vector_distance_l2	Euclidean distance function which operates over vector of same type with same dimensionality

Begin by declaring a column used for storing vectors with the `F32_BLOB` datatype:

```sql  theme={null}
CREATE TABLE movies (
  title     TEXT,
  year      INT,
  embedding F32_BLOB(4) -- 4-dimensional f32 vector
);
```

The number in parentheses `(4)` specifies the dimensionality of the vector. This means each vector in this column will have exactly 4 components.

Once you generate embeddings for your data (via an LLM), you can insert them into your table:

```sql  theme={null}
INSERT INTO movies (title, year, embedding)
VALUES
  ('Napoleon', 2023, vector32('[0.800, 0.579, 0.481, 0.229]')),
  ('Black Hawk Down', 2001, vector32('[0.406, 0.027, 0.378, 0.056]')),
  ('Gladiator', 2000, vector32('[0.698, 0.140, 0.073, 0.125]')),
  ('Blade Runner', 1982, vector32('[0.379, 0.637, 0.011, 0.647]'));
```

Popular tools like [LangChain](https://www.langchain.com), [Hugging Face](https://huggingface.co) or [OpenAI](https://turso.tech/blog/how-to-generate-and-store-openai-vector-embeddings-with-turso) can be used to generate embeddings.

You can now write queries combining vectors and standard SQLite data:

```sql  theme={null}
SELECT title,
       vector_extract(embedding),
       vector_distance_cos(embedding, vector32('[0.064, 0.777, 0.661, 0.687]')) AS distance
FROM movies
ORDER BY distance ASC;
```

The vector_distance_cos function calculates the cosine distance, which is defined as:

• Cosine Distance = 1 — Cosine Similarity

The cosine distance ranges from 0 to 2, where:

• A distance close to 0 indicates that the vectors are nearly identical or exactly matching.
• A distance close to 1 indicates that the vectors are orthogonal (perpendicular).
• A distance close to 2 indicates that the vectors are pointing in opposite directions.

Very small negative numbers close to zero (for example, `-10^-14`) may occasionally appear due to floating-point arithmetic precision. These should be interpreted as effectively zero, indicating an exact or near-exact match between vectors.

SELECT vector_distance_cos('[1000]', '[1000]');
-- Output: -2.0479999918166e-09

• Euclidean distance is not supported for 1-bit FLOAT1BIT vectors
• LibSQL can only operate on vectors with no more than 65536 dimensions

Nearest neighbors (NN) queries are popular for various AI-powered applications (RAG uses NN queries to extract relevant information, and recommendation engines can suggest items based on embedding similarity).

LibSQL implements DiskANN algorithm in order to speed up approximate nearest neighbors queries for tables with vector columns.

The DiskANN algorithm trades search accuracy for speed, so LibSQL queries may return slightly suboptimal neighbors for tables with a large number of rows.

LibSQL introduces a custom index type that helps speed up nearest neighbors queries against a fixed distance function (cosine similarity by default).

From a syntax perspective, the vector index differs from ordinary application-defined B-Tree indices in that it must wrap the vector column into a libsql_vector_idx marker function like this

CREATE INDEX movies_idx ON movies (libsql_vector_idx(embedding));

Vector index works only for column with one of the vector types described above

The vector index is fully integrated into the LibSQL core, so it inherits all operations and most features from ordinary indices:

• An index created for a table with existing data will be automatically populated with this data
• All updates to the base table will be automatically reflected in the index
• You can rebuild index from scratch using REINDEX movies_idx command
• You can drop index with DROP INDEX movies_idx command
• You can create partial vector index with a custom filtering rule:

CREATE INDEX movies_idx ON movies (libsql_vector_idx(embedding))
WHERE year >= 2000;

At the moment vector index must be queried explicitly with special vector_top_k(idx_name, q_vector, k) table-valued function. The function accepts index name, query vector and amount of neighbors to return. This function searches for k approximate nearest neighbors and returns ROWID of these rows or PRIMARY KEY if base index does not have ROWID.

In order for table-valued function to work query vector must have the same vector type and dimensionality.

LibSQL vector index optionally can accept settings which must be specified as variadic parameters of the libsql_vector_idx function as strings in the format key=value:

CREATE INDEX movies_idx
ON movies(libsql_vector_idx(embedding, 'metric=l2', 'compress_neighbors=float8'));

At the moment LibSQL supports the following settings:

Setting key	Value type	Description
metric	cosine | l2	Which distance function to use for building the index. Default: cosine
max_neighbors	positive integer	How many neighbors to store for every node in the DiskANN graph. The lower the setting -- the less storage index will use in exchange to search precision. Default: $3 \sqrt{D}$ where $D$ -- dimensionality of vector column
compress_neighbors	float1bit|float8| float16|floatb16| float32	Which vector type must be used to store neighbors for every node in the DiskANN graph. The more compact vector type is used for neighbors -- the less storage index will use in exchange to search precision. Default: no compression (neighbors has same type as base table)
alpha	positive float $\geq 1$	"Density" parameter of general sparse neighborhood graph build during DiskANN algorithm. The lower parameter -- the more sparse is DiskANN graph which can speed up query speed in exchange to lower search precision. Default: 1.2
search_l	positive integer	Setting which limits the amount of neighbors visited during vector search. The lower the setting -- the faster will be search query in exchange to search precision. Default: 200
insert_l	positive integer	Setting which limits the amount of neighbors visited during vector insert. The lower the setting -- the faster will be insert query in exchange to DiskANN graph navigability properties. Default: 70

Vector index for column of type `T1` with `max_neighbors=M` and `compress_neighbors=T2` will approximately use $\texttt{N} (Storage(\texttt {T1}) + \texttt{M} \cdot Storage(\texttt{T2}))$ storage bytes for `N` rows. Begin by declaring a column used for storing vectors with the `F32_BLOB` datatype:

```sql  theme={null}
CREATE TABLE movies (
  title     TEXT,
  year      INT,
  embedding F32_BLOB(4) -- 4-dimensional f32 vector
);
```

The number in parentheses `(4)` specifies the dimensionality of the vector. This means each vector in this column will have exactly 4 components.

Once you generate embeddings for your data (via an LLM), you can insert them into your table:

```sql  theme={null}
INSERT INTO movies (title, year, embedding)
VALUES
  ('Napoleon', 2023, vector32('[0.800, 0.579, 0.481, 0.229]')),
  ('Black Hawk Down', 2001, vector32('[0.406, 0.027, 0.378, 0.056]')),
  ('Gladiator', 2000, vector32('[0.698, 0.140, 0.073, 0.125]')),
  ('Blade Runner', 1982, vector32('[0.379, 0.637, 0.011, 0.647]'));
```

Popular tools like [LangChain](https://www.langchain.com), [Hugging Face](https://huggingface.co) or [OpenAI](https://turso.tech/blog/how-to-generate-and-store-openai-vector-embeddings-with-turso) can be used to generate embeddings.

Create an index using the `libsql_vector_idx` function:

```sql  theme={null}
CREATE INDEX movies_idx ON movies(libsql_vector_idx(embedding));
```

This creates an index optimized for vector similarity searches on the `embedding` column.

<Note>
  The `libsql_vector_idx` marker function is **required** and used by libSQL to
  distinguish `ANN`-indices from ordinary B-Tree indices.
</Note>

```sql theme={null} SELECT title, year FROM vector_top_k('movies_idx', vector32('[0.064, 0.777, 0.661, 0.687]'), 3) JOIN movies ON movies.rowid = id WHERE year >= 2020; ```

This query uses the `vector_top_k` [table-valued function](https://www.sqlite.org/vtab.html#table_valued_functions) to efficiently find the top 3 most similar vectors to `[0.064, 0.777, 0.661, 0.687]` using the index.

• Vector index works only for tables with ROWID or with singular PRIMARY KEY. Composite PRIMARY KEY without ROWID is not supported