Native Rust implementation of Apache Arrow
Welcome to the implementation of Arrow, the popular in-memory columnar format, in Rust.
This part of the Arrow project is divided in 4 main components:
Crate | Description | Documentation |
---|---|---|
Arrow | Core functionality (memory layout, arrays, low level computations) | (README) |
Parquet | Parquet support | (README) |
Arrow-flight | Arrow data between processes | (README) |
DataFusion | In-memory query engine with SQL support | (README) |
Ballista | Distributed query execution | (README) |
Independently, they support a vast array of functionality for in-memory computations.
Together, they allow users to write an SQL query or a DataFrame
(using the datafusion
crate), run it against a parquet file (using the parquet
crate), evaluate it in-memory using Arrow's columnar format (using the arrow
crate), and send to another process (using the arrow-flight
crate).
Generally speaking, the arrow
crate offers functionality to develop code that uses Arrow arrays, and datafusion
offers most operations typically found in SQL, with the notable exceptions of:
join
window
functions
There are too many features to enumerate here, but some notable mentions:
Arrow
implements all formats in the specification except certain dictionariesArrow
supports SIMD operations to some of its vertical operationsDataFusion
supportsasync
executionDataFusion
supports user-defined functions, aggregates, and whole execution nodes
You can find more details about each crate in their respective READMEs.
Arrow Rust Community
We use the official ASF Slack for informal discussions and coordination. This is a great place to meet other contributors and get guidance on where to contribute. Join us in the arrow-rust
channel.
We use ASF JIRA as the system of record for new features and bug fixes and this plays a critical role in the release process.
For design discussions we generally collaborate on Google documents and file a JIRA linking to the document.
There is also a bi-weekly Rust-specific sync call for the Arrow Rust community. This is hosted on Google Meet at https://meet.google.com/ctp-yujs-aee on alternate Wednesday's at 09:00 US/Pacific, 12:00 US/Eastern. During US daylight savings time this corresponds to 16:00 UTC and at other times this is 17:00 UTC.
Developer's guide to Arrow Rust
How to compile
This is a standard cargo project with workspaces. To build it, you need to have rust
and cargo
:
cd /rust && cargo build
You can also use rust's official docker image:
docker run --rm -v $(pwd)/rust:/rust -it rust /bin/bash -c "cd /rust && cargo build"
The command above assumes that are in the root directory of the project, not in the same directory as this README.md.
You can also compile specific workspaces:
cd /rust/arrow && cargo build
Git Submodules
Before running tests and examples, it is necessary to set up the local development environment.
The tests rely on test data that is contained in git submodules.
To pull down this data run the following:
git submodule update --init
This populates data in two git submodules:
../parquet_testing/data
(sourced from https://github.com/apache/parquet-testing.git)../testing
(sourced from https://github.com/apache/arrow-testing)
By default, cargo test
will look for these directories at their standard location. The following environment variables can be used to override the location:
# Optionaly specify a different location for test data
export PARQUET_TEST_DATA=$(cd ../parquet-testing/data; pwd)
export ARROW_TEST_DATA=$(cd ../testing/data; pwd)
From here on, this is a pure Rust project and cargo
can be used to run tests, benchmarks, docs and examples as usual.
Running the tests
Run tests using the Rust standard cargo test
command:
# run all tests.
cargo test
# run only tests for the arrow crate
cargo test -p arrow
Code Formatting
Our CI uses rustfmt
to check code formatting. Before submitting a PR be sure to run the following and check for lint issues:
cargo +stable fmt --all -- --check
Clippy Lints
We recommend using clippy
for checking lints during development. While we do not yet enforce clippy
checks, we recommend not introducing new clippy
errors or warnings.
Run the following to check for clippy lints.
cargo clippy
If you use Visual Studio Code with the rust-analyzer
plugin, you can enable clippy
to run each time you save a file. See https://users.rust-lang.org/t/how-to-use-clippy-in-vs-code-with-rust-analyzer/41881.
One of the concerns with clippy
is that it often produces a lot of false positives, or that some recommendations may hurt readability. We do not have a policy of which lints are ignored, but if you disagree with a clippy
lint, you may disable the lint and briefly justify it.
Search for allow(clippy::
in the codebase to identify lints that are ignored/allowed. We currently prefer ignoring lints on the lowest unit possible.
- If you are introducing a line that returns a lint warning or error, you may disable the lint on that line.
- If you have several lints on a function or module, you may disable the lint on the function or module.
- If a lint is pervasive across multiple modules, you may disable it at the crate level.
Git Pre-Commit Hook
We can use git pre-commit hook to automate various kinds of git pre-commit checking/formatting.
Suppose you are in the root directory of the project.
First check if the file already exists:
ls -l .git/hooks/pre-commit
If the file already exists, to avoid mistakenly overriding, you MAY have to check the link source or file content. Else if not exist, let's safely soft link pre-commit.sh as file .git/hooks/pre-commit
:
ln -s ../../rust/pre-commit.sh .git/hooks/pre-commit
If sometimes you want to commit without checking, just run git commit
with --no-verify
:
git commit --no-verify -m "... commit message ..."