Extensions
- vector 0.4.1
- Open-source vector similarity search for Postgres
Documentation
- CHANGELOG
- CHANGELOG
README
Contents
pgvector
Open-source vector similarity search for Postgres
sql
CREATE TABLE items (embedding vector(3));
CREATE INDEX ON items USING ivfflat (embedding vector_l2_ops);
SELECT * FROM items ORDER BY embedding <-> '[1,2,3]' LIMIT 5;
Supports L2 distance, inner product, and cosine distance
Installation
Compile and install the extension (supports Postgres 11+)
sh
git clone --branch v0.4.1 https://github.com/pgvector/pgvector.git
cd pgvector
make
make install # may need sudo
Then load it in databases where you want to use it
sql
CREATE EXTENSION vector;
You can also install it with Docker, Homebrew, PGXN, or conda-forge
Getting Started
Create a vector column with 3 dimensions
sql
CREATE TABLE items (embedding vector(3));
Insert values
sql
INSERT INTO items VALUES ('[1,2,3]'), ('[4,5,6]');
Get the nearest neighbor by L2 distance
sql
SELECT * FROM items ORDER BY embedding <-> '[3,1,2]' LIMIT 1;
Also supports inner product (<#>
) and cosine distance (<=>
)
Note: <#>
returns the negative inner product since Postgres only supports ASC
order index scans on operators
Querying
Use a SELECT
clause to get the distance
sql
SELECT embedding <-> '[3,1,2]' AS distance FROM items;
Use a WHERE
clause to get rows within a certain distance
sql
SELECT * FROM items WHERE embedding <-> '[3,1,2]' < 5;
Note: Combine with ORDER BY
and LIMIT
to use an index
Get the average of vectors
sql
SELECT AVG(embedding) FROM items;
Indexing
Speed up queries with an approximate index. Add an index for each distance function you want to use.
L2 distance
sql
CREATE INDEX ON items USING ivfflat (embedding vector_l2_ops);
Inner product
sql
CREATE INDEX ON items USING ivfflat (embedding vector_ip_ops);
Cosine distance
sql
CREATE INDEX ON items USING ivfflat (embedding vector_cosine_ops);
Indexes should be created after the table has some data for optimal clustering. Also, unlike typical indexes which only affect performance, you may see different results for queries after adding an approximate index. Vectors with up to 2,000 dimensions can be indexed.
Index Options
Specify the number of inverted lists (100 by default)
sql
CREATE INDEX ON items USING ivfflat (embedding vector_l2_ops) WITH (lists = 100);
A good place to start is 4 * sqrt(rows)
Query Options
Specify the number of probes (1 by default)
sql
SET ivfflat.probes = 1;
A higher value improves recall at the cost of speed, and it can be set to the number of lists for exact nearest neighbor search (at which point the planner won’t use the index)
Use SET LOCAL
inside a transaction to set it for a single query
sql
BEGIN;
SET LOCAL ivfflat.probes = 1;
SELECT ...
COMMIT;
Indexing Progress
Check indexing progress with Postgres 12+
sql
SELECT phase, tuples_done, tuples_total FROM pg_stat_progress_create_index;
The phases are:
initializing
performing k-means
sorting tuples
loading tuples
Note: tuples_done
and tuples_total
are only populated during the loading tuples
phase
Partial Indexes
Consider partial indexes for queries with a WHERE
clause
sql
SELECT * FROM items WHERE category_id = 123 ORDER BY embedding <-> '[3,1,2]' LIMIT 5;
can be indexed with:
sql
CREATE INDEX ON items USING ivfflat (embedding vector_l2_ops) WHERE (category_id = 123);
To index many different values of category_id
, consider partitioning on category_id
.
sql
CREATE TABLE items (embedding vector(3), category_id int) PARTITION BY LIST(category_id);
Performance
To speed up queries without an index, increase max_parallel_workers_per_gather
.
sql
SET max_parallel_workers_per_gather = 4;
To speed up queries with an index, increase the number of inverted lists (at the expense of recall).
sql
CREATE INDEX ON items USING ivfflat (embedding vector_l2_ops) WITH (lists = 1000);
Use EXPLAIN ANALYZE
to debug performance.
sql
EXPLAIN ANALYZE SELECT * FROM items ORDER BY embedding <-> '[3,1,2]' LIMIT 1;
Languages
Use pgvector from any language with a Postgres client. You can even generate and store vectors in one language and query them in another.
Language | Libraries / Examples --- | --- C++ | pgvector-cpp C# | pgvector-dotnet Elixir | pgvector-elixir Go | pgvector-go Java, Scala | pgvector-java Julia | pgvector-julia Lua | pgvector-lua Node.js | pgvector-node PHP | pgvector-php Python | pgvector-python R | pgvector-r Ruby | pgvector-ruby, Neighbor Rust | pgvector-rust
Frequently Asked Questions
How many vectors can be stored in a single table?
A non-partitioned table has a limit of 32 TB by default in Postgres. A partitioned table can have thousands of partitions of that size.
Is replication supported?
Yes, pgvector uses the write-ahead log (WAL), which allows for replication and point-in-time recovery.
What if I want to index vectors with more than 2,000 dimensions?
Two things you can try are:
- use dimensionality reduction
- compile Postgres with a larger block size (
./configure --with-blocksize=32
) and edit the limit insrc/ivfflat.h
Reference
Vector Type
Each vector takes 4 * dimensions + 8
bytes of storage. Each element is a single precision floating-point number (like the real
type in Postgres), and all elements must be finite (no NaN
, Infinity
or -Infinity
). Vectors can have up to 16,000 dimensions.
Vector Operators
Operator | Description --- | --- + | element-wise addition - | element-wise subtraction <-> | Euclidean distance <#> | negative inner product <=> | cosine distance
Vector Functions
Function | Description --- | --- cosine_distance(vector, vector) → double precision | cosine distance inner_product(vector, vector) → double precision | inner product l2_distance(vector, vector) → double precision | Euclidean distance vector_dims(vector) → integer | number of dimensions vector_norm(vector) → double precision | Euclidean norm
Aggregate Functions
Function | Description --- | --- avg(vector) → vector | arithmetic mean
Additional Installation Methods
Docker
Get the Docker image with:
sh
docker pull ankane/pgvector
This adds pgvector to the Postgres image (run it the same way).
You can also build the image manually:
sh
git clone --branch v0.4.1 https://github.com/pgvector/pgvector.git
cd pgvector
docker build -t pgvector .
Homebrew
With Homebrew Postgres, you can use:
sh
brew install pgvector/brew/pgvector
PGXN
Install from the PostgreSQL Extension Network with:
sh
pgxn install vector
conda-forge
With Conda Postgres, install from conda-forge with:
sh
conda install -c conda-forge pgvector
This method is community-maintained by @mmcauliffe
Hosted Postgres
pgvector is available on these providers.
To request a new extension on other providers:
- Amazon RDS - follow the instructions on this page
- Google Cloud SQL - vote or comment on this page
- DigitalOcean Managed Databases - vote or comment on this page
- Azure Database - vote or comment on this page
Upgrading
Install the latest version and run:
sql
ALTER EXTENSION vector UPDATE;
Upgrade Notes
0.4.0
If upgrading with Postgres < 13, remove this line from sql/vector--0.3.2--0.4.0.sql
:
sql
ALTER TYPE vector SET (STORAGE = extended);
Then run make install
and ALTER EXTENSION vector UPDATE;
.
0.3.1
If upgrading from 0.2.7 or 0.3.0, recreate all ivfflat
indexes after upgrading to ensure all data is indexed.
```sql -- Postgres 12+ REINDEX INDEX CONCURRENTLY index_name;
-- Postgres < 12 CREATE INDEX CONCURRENTLY temp_name ON table USING ivfflat (column opclass); DROP INDEX CONCURRENTLY index_name; ALTER INDEX temp_name RENAME TO index_name; ```
Thanks
Thanks to:
- PASE: PostgreSQL Ultra-High-Dimensional Approximate Nearest Neighbor Search Extension
- Faiss: A Library for Efficient Similarity Search and Clustering of Dense Vectors
- Using the Triangle Inequality to Accelerate k-means
- k-means++: The Advantage of Careful Seeding
- Concept Decompositions for Large Sparse Text Data using Clustering
History
View the changelog
Contributing
Everyone is encouraged to help improve this project. Here are a few ways you can help:
- Report bugs
- Fix bugs and submit pull requests
- Write, clarify, or fix documentation
- Suggest or add new features
To get started with development:
sh
git clone https://github.com/pgvector/pgvector.git
cd pgvector
make
make install
To run all tests:
sh
make installcheck # regression tests
make prove_installcheck # TAP tests
To run single tests:
sh
make installcheck REGRESS=functions # regression test
make prove_installcheck PROVE_TESTS=test/t/001_wal.pl # TAP test
To enable benchmarking:
sh
make clean && PG_CFLAGS=-DIVFFLAT_BENCH make && make install
Resources for contributors