Simon Willison’s Weblog

Introducing Limbo: A complete rewrite of SQLite in Rust (via) This looks absurdly ambitious:

Our goal is to build a reimplementation of SQLite from scratch, fully compatible at the language and file format level, with the same or higher reliability SQLite is known for, but with full memory safety and on a new, modern architecture.

The Turso team behind it have been maintaining their libSQL fork for two years now, so they're well equipped to take on a challenge of this magnitude.

SQLite is justifiably famous for its meticulous approach to testing. Limbo plans to take an entirely different approach based on "Deterministic Simulation Testing" - a modern technique pioneered by FoundationDB and now spearheaded by Antithesis, the company Turso have been working with on their previous testing projects.

Another bold claim (emphasis mine):

We have both added DST facilities to the core of the database, and partnered with Antithesis to achieve a level of reliability in the database that lives up to SQLite’s reputation.

[...] With DST, we believe we can achieve an even higher degree of robustness than SQLite, since it is easier to simulate unlikely scenarios in a simulator, test years of execution with different event orderings, and upon finding issues, reproduce them 100% reliably.

The two most interesting features that Limbo is planning to offer are first-party WASM support and fully asynchronous I/O:

SQLite itself has a synchronous interface, meaning driver authors who want asynchronous behavior need to have the extra complication of using helper threads. Because SQLite queries tend to be fast, since no network round trips are involved, a lot of those drivers just settle for a synchronous interface. [...]

Limbo is designed to be asynchronous from the ground up. It extends sqlite3_step, the main entry point API to SQLite, to be asynchronous, allowing it to return to the caller if data is not ready to consume immediately.

Datasette provides an async API for executing SQLite queries which is backed by all manner of complex thread management - I would be very interested in a native asyncio Python library for talking to SQLite database files.

I successfully tried out Limbo's Python bindings against a demo SQLite test database using uv like this:

uv run --with pylimbo python
>>> import limbo
>>> conn = limbo.connect("/tmp/demo.db")
>>> cursor = conn.cursor()
>>> print(cursor.execute("select * from foo").fetchall())

It crashed when I tried against a more complex SQLite database that included SQLite FTS tables.

The Python bindings aren't yet documented, so I piped them through LLM and had the new google-exp-1206 model write this initial documentation for me:

files-to-prompt limbo/bindings/python -c | llm -m gemini-exp-1206 -s 'write extensive usage documentation in markdown, including realistic usage examples'