aiocoalesce

A best-in-class async request coalescing library for Python (3.9+).

aiocoalesce ensures that multiple concurrent async requests for the same key share a single execution (the "SingleFlight" pattern). This protects your backend from Thundering Herds without the complexity of Redis or caching layers.

Key Difference: Unlike other libraries, aiocoalesce is Cancellation Safe. If the first user disconnects, the shared work continues for other waiting users.

Installation

pip install aiocoalesce

Usage

import asyncio
from aiocoalesce import Coalescer

# Create a global coalescer
coalescer = Coalescer()

async def get_user_data(user_id: int):
    # Simulate DB call
    await asyncio.sleep(1)
    return {"id": user_id, "name": "Alice"}

# In your API handler:
async def handler(user_id):
    # If 10 requests come in at once for user_id=1, 
    # 'get_user_data' runs ONLY ONCE.
    return await coalescer.run(user_id, get_user_data(user_id))

Why aiocoalesce?

Use Case

Perfect for:

• FastAPI endpoints with expensive DB queries.
• ML Inference servers (prevent running same model input twice).
• Proxy servers to reduce upstream load.

License

MIT