Chancy

A postgres-backed task queue for Python.

Key Features:

• Jobs support priorities, retries, timeouts, scheduling, global rate limits, memory limits, global uniqueness, error capture, cancellation, and more

• Minimal dependencies (only psycopg3 required)

• Plugins for a dashboard, workflows, cron jobs, and much more

• Optional transactional enqueueing for atomic job creation

• asyncio & sync APIs for easy integration with existing codebases

• 100% open & free - no enterprise or paid features. Checkout the repo on GitHub.

Quick Start

CLI

Install Chancy & its CLI:

pip install chancy[cli]

Create a new file called worker.py:

worker.py

from chancy import Chancy, job

@job(queue="default")
def hello_world(*, name: str):
    print(f"Hello, {name}!")

chancy = Chancy("postgresql://localhost/postgres")

Then run the database migrations:

chancy --app worker.chancy misc migrate

Declare a queue:

chancy --app worker.chancy queue declare default --concurrency 10

Push a job:

chancy --app worker.chancy queue push worker.hello_world --kwargs '{"name": "world"}'

Start a worker:

chancy --app worker.chancy worker start

Code

Install Chancy:

pip install chancy

Create a new file called worker.py:

worker.py

 import asyncio
 from chancy import Chancy, Worker, Queue, job

 @job(queue="default")
 def hello_world(*, name: str):
     print(f"Hello, {name}!")

 chancy = Chancy("postgresql://localhost/postgres")

 async def main():
     async with chancy:
         # Run the database migrations
         await chancy.migrate()
         # Declare a queue
         await chancy.declare(Queue("default", concurrency=10))
         # Push a job
         await chancy.push(hello_world.job.with_kwargs(name="World"))
         # Start the worker (ctrl+c to exit)
         async with Worker(chancy) as worker:
             await worker.wait_for_shutdown()

 if __name__ == "__main__":
     asyncio.run(main())

Congratulations! You’ve just run your first Chancy job. Next, explore the How To or plugins.

Dashboard

Chancy comes with a built-in dashboard - no need to run a separate service like Flower.

Similar Projects

With the addition of modern Postgres features like LISTEN/NOTIFY and SELECT FOR UPDATE...SKIP LOCKED, postgres-backed task queues have become a viable alternative to other task queues built on RabbitMQ or redis like celery. As such the space is exploding with new projects. Here are some of the most popular ones if Chancy doesn’t fit your needs:

Project	Language	Note
celery	Python	The defacto Python task queue
procastinate	Python
oban	Elixir	Inspired many of the features in Chancy
river	Go
neoq	Go
faktory	Go
pg-boss	Node.js
graphile	Node.js
Minion	Perl

Indices and tables

• Index

• Module Index

• Search Page