DataFusion on Ray

This was originally a research project donated from ray-sql to evaluate performing distributed SQL queries from Python, using Ray and Apache DataFusion

DataFusion Ray is a distributed Python DataFrame and SQL query engine powered by the Rust implementation of Apache Arrow, Apache DataFusion, and Ray.

Comparison to other DataFusion projects

Comparison to DataFusion Ballista

• Unlike DataFusion Ballista, DataFusion Ray does not provide its own distributed scheduler and instead relies on Ray for this functionality. As a result of this design choice, DataFusion Ray is a much smaller and simpler project.
• DataFusion Ray is Python-first, and DataFusion Ballista is Rust-first

Comparison to DataFusion Python

• DataFusion Python provides a Python DataFrame and SQL API for in-process execution. DataFusion Ray extends DataFusion Python to provide scalability across multiple nodes.

Example

Run the following example live in your browser using a Google Colab notebook.

import os
import ray

from datafusion_ray import DatafusionRayContext

SCRIPT_DIR = os.path.dirname(os.path.realpath(__file__))

# Start a local cluster
ray.init(resources={"worker": 1})

# Create a context and register a table
ctx = DatafusionRayContext(2)
# Register either a CSV or Parquet file
# ctx.register_csv("tips", f"{SCRIPT_DIR}/tips.csv", True)
ctx.register_parquet("tips", f"{SCRIPT_DIR}/tips.parquet")

result_set = ctx.sql(
  "select sex, smoker, avg(tip/total_bill) as tip_pct from tips group by sex, smoker"
)
for record_batch in result_set:
  print(record_batch.to_pandas())

Status

• DataFusion Ray can run all queries in the TPC-H benchmark

Features

• Mature SQL support (CTEs, joins, subqueries, etc) thanks to DataFusion
• Support for CSV and Parquet files

Building

# prepare development environment (used to build wheel / install in development)
python3 -m venv venv
# activate the venv
source venv/bin/activate
# update pip itself if necessary
python -m pip install -U pip
# install dependencies (for Python 3.8+)
python -m pip install -r requirements-in.txt

Whenever rust code changes (your changes or via git pull):

# make sure you activate the venv using "source venv/bin/activate" first
maturin develop; python -m pytest 

Testing

Running local Rust tests require generating the tpch-data. This can be done by running the following commands:

export TPCH_TEST_PARTITIONS=1
export TPCH_SCALING_FACTOR=1
./scripts/gen-test-data.sh

This will generate data into a top-level data directory.

Tests can be run with:

export TPCH_DATA_PATH=`pwd`/data
cargo test

Benchmarking

Create a release build when running benchmarks, then use pip to install the wheel.

maturin develop --release

How to update dependencies

To change test dependencies, change the requirements.in and run

# install pip-tools (this can be done only once), also consider running in venv
python -m pip install pip-tools
python -m piptools compile --generate-hashes -o requirements-310.txt

To update dependencies, run with -U

python -m piptools compile -U --generate-hashes -o requirements-310.txt

More details here