Sawtooth 🪚

Sawtooth is a utility for congestion control using additive increase and multiplicative backoff. The algorithm is based on this blog post.

Getting started

pip install sawtooth

Basic usage

from sawtooth import Sawtooth, SawtoothBackpressure
import asyncio
from aiohttp import ClientSession 
from aiohttp.web_exceptions import HTTPTooManyRequests

async def main():
    session = ClientSession()
    sawtooth = Sawtooth(session)

    with open('urls.txt') as f:
        urls = f.readlines()
    
    async def get_url(url: str):
        async with sawtooth.resource() as s:
            res = await s.get(url)
            # Raise backpressure on 429
            if res.status == HTTPTooManyRequests.status_code:
                raise SawtoothBackpressure()

    await asyncio.gather(*[get_url(url) for url in urls])

    await session.close()

Configuration

A Sawtooth instance can be configured by passing an instance of SawtoothConfig as its second parameter.

sawtooth = Sawtooth(resource, SawtoothConfig(max_concurrency=100, min_concurrency=50))

The following options are available:

Name	Description	Default
max_concurrency	The maximum value we can increase concurrency to	1000
min_concurrency	The minimum value we can reduce concurrency to	1
step_size	The amount to increase concurrency by on a successful response	1
backoff_factor	Reduce concurrency to concurrency * backoff_factor upon receiving backpressure	0.95
starting_concurrency	Starting concurrency.	(max_concurrency - min_concurrency) / 2