limbo/CONTRIBUTING.md

Contributing to Turso

We'd love to have you contribute to Turso!

This document is a quick helper to get you going.

Getting Started

Turso is a rewrite of SQLite in Rust. If you are new to SQLite, the following articles and books are a good starting point:

• Architecture of SQLite
• Sibsankar Haldar. SQLite Database System Design and Implementation (2nd Edition). 2016
• Jay Kreibich. Using SQLite: Small. Fast. Reliable. Choose Any Three. 1st Edition. 2010

If you are new to Rust, the following books are recommended reading:

• Jim Blandy et al. Programming Rust, 2nd Edition. 2021
• Steve Klabnik and Carol Nichols. The Rust Programming Language. 2022

Examples of contributing

• How to contribute a SQL function implementation

To build and run tursodb CLI:

cargo run --package turso_cli --bin tursodb database.db

Run tests:

cargo test

Running Tests On Linux

Note

These steps have been tested on Ubuntu Noble 24.04.2 LTS

Running tests on Linux and getting them pass requires a few additional steps

1. Install SQLite headers

sudo apt install sqlite3 libsqlite3-dev

2. Install Python3 dev files

sudo apt install python3.12 python3.12-dev

3. Set env var for Maturin

export PYO3_PYTHON=$(which python3)

4. Build Cargo

cargo build -p limbo_sqlite3 --features capi

5. Run tests

cargo test

Test coverage report:

cargo tarpaulin -o html

Note

Generation of coverage report requires tarpaulin binary to be installed. You can install it with cargo install cargo-tarpaulin

Tip

If coverage fails with "Test failed during run" error and all of the tests passed it might be the result of tarpaulin bug. You can temporarily set dynamic libraries linking manually as a workaround, e.g. for linux LD_LIBRARY_PATH="$(rustc --print=target-libdir)" cargo tarpaulin -o html.

Run benchmarks:

cargo bench

Run benchmarks and generate flamegraphs:

echo -1 | sudo tee /proc/sys/kernel/perf_event_paranoid
cargo bench --bench benchmark -- --profile-time=5

Finding things to work on

The issue tracker has issues tagged with good first issue, which are considered to be things to work on to get going. If you're interested in working on one of them, comment on the issue tracker, and we're happy to help you get going.

Submitting your work

Fork the repository and open a pull request to submit your work.

The CI checks for formatting, Clippy warnings, and test failures so remember to run the following before submitting your pull request:

• cargo fmt and cargo clippy to keep the code formatting in check.
• make to run the test suite.

Keep your pull requests focused and as small as possible, but not smaller. IOW, when preparing a pull request, ensure it focuses on a single thing and that your commits align with that. For example, a good pull request might fix a specific bug or a group of related bugs. Or a good pull request might add a new feature and test for it. Conversely, a bad pull request might fix a bug, add a new feature, and refactor some code.

The commits in your pull request tell the story of your change. Break your pull request into multiple commits when needed to make it easier to review and ensure that future developers can also understand the change as they are in the middle of a git bisect run to debug a nasty bug. A developer should be able to reconstruct the intent of your change and how you got to the end-result by reading the commits. To keep a clean commit history, make sure the commits are atomic:

• Keep commits as small as possible. The smaller the commit, the easier it is to review, but also easier git revert when things go bad.
• Don't mix logic and cleanups in same commit. If you need to refactor the code, do it in a commit of its own. Mixing refactoring with logic changes makes it very hard to review a commit.
• Don't mix logic and formatting changes in same commit. Resist the urge to fix random formatting issues in the same commit as your logic changes, because it only makes it harder to review the commit.
• Write a good commit message. You know your commit is atomic when it's easy to write a short commit message that describes the intent of the change.

To produce pull requests like this, you should learn how to use Git's interactive rebase (git rebase -i).

For a longer discussion on good commits, see Al Tenhundfeld's What makes a good git commit, for example.

Debugging query execution

Turso aims towards SQLite compatibility. If you find a query that has different behavior than SQLite, the first step is to check what the generated bytecode looks like.

To do that, first run the EXPLAIN command in sqlite3 shell:

sqlite> EXPLAIN SELECT first_name FROM users;
addr  opcode         p1    p2    p3    p4             p5  comment
----  -------------  ----  ----  ----  -------------  --  -------------
0     Init           0     7     0                    0   Start at 7
1     OpenRead       0     2     0     2              0   root=2 iDb=0; users
2     Rewind         0     6     0                    0
3       Column         0     1     1                    0   r[1]= cursor 0 column 1
4       ResultRow      1     1     0                    0   output=r[1]
5     Next           0     3     0                    1
6     Halt           0     0     0                    0
7     Transaction    0     0     1     0              1   usesStmtJournal=0
8     Goto           0     1     0                    0

and then run the same command in Turso's shell.

If the bytecode is different, that's the bug -- work towards fixing code generation. If the bytecode is the same, but query results are different, then the bug is somewhere in the virtual machine interpreter or storage layer.

Compatibility tests

The testing/test.all is a starting point for adding functional tests using a similar syntax to SQLite. The purpose of these tests is to verify behavior matches with SQLite and Turso.

Prerequisites

1. Cargo-c is needed for building C-ABI compatible library. You can get it via:

cargo install cargo-c

2. SQLite is needed for compatibility checking. You can install it using brew on macOS/Linux:

brew install sqlite

Or using choco on Windows:

choco install sqlite

Running the tests

To run the test suite with Turso, simply run:

make test

To run the test suite with SQLite, type:

SQLITE_EXEC=sqlite3 SQLITE_FLAGS="" make test

When working on a new feature, please consider adding a test case for it.

TPC-H

TPC-H is a standard benchmark for testing database performance. To try out Turso's performance against a TPC-H compatible workload, you can generate or download a TPC-H compatible SQLite database e.g. here.

Deterministic simulation tests

The simulator directory contains a deterministic simulator for testing. What this means is that the behavior of a test run is deterministic based on the seed value. If the simulator catches a bug, you can always reproduce the exact same sequence of events by passing the same seed. The simulator also performs fault injection to discover interesting bugs.

Python Bindings

Turso provides Python bindings built on top of the PyO3 project. To compile the Python bindings locally, you first need to create and activate a Python virtual environment (for example, with Python 3.12):

python3.12 -m venv venv
source venv/bin/activate

Then, install Maturin:

pip install maturin

Once Maturin is installed, you can build the crate and install it as a Python module directly into the current virtual environment by running:

cd bindings/python && maturin develop

Antithesis

Antithesis is a testing platform for finding bugs with reproducibility. In Turso, we use Antithesis in addition to our own deterministic simulation testing (DST) tool for the following:

• Discovering bugs that the DST did not catch (and improve the DST)
• Discovering bugs that the DST does not cover (for example, non-simulated I/O)

If you have an Antithesis account, you first need to configure some environment variables:

export ANTITHESIS_USER=
export ANTITHESIS_TENANT=
export ANTITHESIS_PASSWD=
export ANTITHESIS_DOCKER_HOST=
export ANTITHESIS_DOCKER_REPO=
export ANTITHESIS_EMAIL=

You can then publish a new Antithesis workflow with:

scripts/antithesis/publish-workload.sh

And launch an Antithesis test run with:

scripts/antithesis/launch.sh

Adding Third Party Dependencies

When you want to add third party dependencies, please follow these steps:

1. Add Licenses: Place the appropriate licenses for the third-party dependencies under the licenses directory. Ensure that each license is in a separate file and named appropriately.
2. Update NOTICE.md: Specify the licenses for the third-party dependencies in the NOTICE.md file. Include the name of the dependency, the license file path, and the homepage of the dependency.

By following these steps, you ensure that all third-party dependencies are properly documented and their licenses are included in the project.