sqlite-vector

A Crystal shard that installs and loads SQLite Vector using the official crystal-sqlite3 adapter. Vector operations remain ordinary SQL.

Installation

Requires Crystal 1.21.1 or newer and a system SQLite library with runtime extension loading enabled. The shard uses crystal-sqlite3 ~> 0.24.0; it does not replace SQLite or require an adapter fork.

On macOS, Apple's SQLite may omit the extension-loading entry point. Install Homebrew SQLite and tell Crystal's linker where to find it before compiling:

brew install sqlite
export CRYSTAL_LIBRARY_PATH="$(brew --prefix sqlite)/lib:$(crystal env CRYSTAL_LIBRARY_PATH)"

Without a SQLite library that exports sqlite3_load_extension, compilation can fail with an undefined-symbol error. On Linux, install the SQLite development package for your distribution (libsqlite3-dev on Debian/Ubuntu, sqlite-dev on Alpine).

Add the dependency to shard.yml:

dependencies:
  sqlite-vector:
    github: krthr/sqlite-vector

Run shards install. Its postinstall hook downloads SQLite Vector 1.1.2 from the upstream release, verifies its pinned SHA-256 checksum, and installs the shared library under lib/sqlite-vector/native/. Installation needs curl, tar, and sha256sum or shasum; Linux also needs ldd to identify libc.

Supported native platforms:

If you use shards install --skip-postinstall, run the installer yourself:

sh lib/sqlite-vector/scripts/install.sh

Installation requires network access; running the application does not download anything. Unsupported platforms and installation failures produce errors.

Usage

require "sqlite-vector"

DB.open("sqlite3://./app.db") do |db|
  db.setup_connection do |connection|
    Sqlite::Vector.load(connection.as(SQLite3::Connection))
  end

  puts db.scalar("SELECT vector_version()")
end

Load the extension before running vector queries. setup_connection initializes both existing connections and connections created later by the pool. If your application already has a setup block, add the loader there: registering another block replaces the previous one.

The public methods are:

Sqlite::Vector.extension_path : String
Sqlite::Vector.load(connection : SQLite3::Connection,
                   path : String = extension_path) : Nil

extension_path returns the installed library's absolute path. load uses SQLite's C loading API and disables extension loading after a native load attempt, including on failure. Invalid inputs are rejected before changing the connection. It does not enable SQL's load_extension() function. Failures raise Sqlite::Vector::Error, with SQLite's return code in code when available. Only load libraries you trust.

Loading failures raise Sqlite::Vector::Error, a DB::Error subclass. Its code property contains SQLite's return code when the failure came from SQLite.

Vector queries

Create the table first, then call vector_init in the setup block for every connection that will use it:

require "sqlite-vector"

DB.open("sqlite3://./app.db") do |db|
  db.using_connection do |connection|
    connection.exec "CREATE TABLE IF NOT EXISTS documents (id INTEGER PRIMARY KEY, embedding BLOB)"
  end

  db.setup_connection do |connection|
    Sqlite::Vector.load(connection.as(SQLite3::Connection))
    connection.scalar "SELECT vector_init('documents', 'embedding', 'type=FLOAT32,dimension=3')"
  end

  db.exec "INSERT OR REPLACE INTO documents VALUES (1, vector_as_f32(?))", "[1,0,0]"
  db.exec "INSERT OR REPLACE INTO documents VALUES (2, vector_as_f32(?))", "[0,1,0]"
  ids = db.query_all(
    "SELECT rowid FROM vector_full_scan('documents', 'embedding', vector_as_f32(?), 1)",
    "[1,0,0]", as: Int64
  )
  puts ids # => [1]
end

Table initialization is connection-local; loading the extension alone does not initialize your tables. Register setup before starting application queries, and keep schema creation in using_connection as shown. See the upstream SQL API for distances, quantization, and other vector operations.

Deployment

The compiled Crystal executable does not embed the downloaded library. Copy the appropriate file from lib/sqlite-vector/native/<platform>/ into your deployment and pass its runtime path:

Sqlite::Vector.load(connection.as(SQLite3::Connection),
  path: "/opt/my-app/lib/vector.so")

Use vector.dylib on macOS. The default path points into the source checkout; an explicit deployment path lets the executable run without that checkout. Ship the upstream license and third-party notice with the library.

Build and install on the target OS, CPU architecture, and libc. Cross-compilation, Windows, fully static executables, and embedding the extension are not supported by this shard. A matching extension binary still requires a compatible system SQLite build; builds with SQLITE_OMIT_LOAD_EXTENSION cannot load it.

Development

shards install
sh scripts/install.sh
sh scripts/test_install.sh
crystal spec
sh scripts/test_deployment.sh
crystal tool format --check

The root project's postinstall hook is not run by shards install, so development requires the explicit installer command. Integration specs use the real extension. The deployment smoke test installs a fresh downstream project, compiles it, and runs it with a copied library after removing its temporary source checkout.

CI is configured for all six OS/architecture/libc combinations above.

License

The Crystal wrapper is MIT licensed. SQLite Vector is separately Apache-2.0 licensed, copyright SQLite Cloud, Inc.