Making 1 milion requests with aiohttp/asyncio - literally

Question

I followed up this tutorial: https://pawelmhm.github.io/asyncio/python/aiohttp/2016/04/22/asyncio-aiohttp.html and everything works fine when I am doing like 50 000 requests. But I need to do 1 milion API calls and then I have problem with this code:

    url = "http://some_url.com/?id={}"
    tasks = set()

    sem = asyncio.Semaphore(MAX_SIM_CONNS)
    for i in range(1, LAST_ID + 1):
        task = asyncio.ensure_future(bound_fetch(sem, url.format(i)))
        tasks.add(task)

    responses = asyncio.gather(*tasks)
    return await responses

Because Python needs to create 1 milion tasks, it basically just lags and then prints Killed message in terminal. Is there any way to use a generator insted of pre-made set (or list) of urls? Thanks.

Answer 1

asyncio is memory bound (like any other program). You can not spawn more task that memory can hold. My guess is that you hit a memory limit. Check dmesg for more information.

1 millions RPS doesn't mean there is 1M tasks. A task can do several request in the same second.

Answer 2

Schedule all 1 million tasks at once

This is the code you are talking about. It takes up to 3 GB RAM so it is easily possible that it will be terminated by the operating system if you have low free memory.

import asyncio
from aiohttp import ClientSession

MAX_SIM_CONNS = 50
LAST_ID = 10**6

async def fetch(url, session):
    async with session.get(url) as response:
        return await response.read()

async def bound_fetch(sem, url, session):
    async with sem:
        await fetch(url, session)

async def fetch_all():
    url = "http://localhost:8080/?id={}"
    tasks = set()
    async with ClientSession() as session:
        sem = asyncio.Semaphore(MAX_SIM_CONNS)
        for i in range(1, LAST_ID + 1):
            task = asyncio.create_task(bound_fetch(sem, url.format(i), session))
            tasks.add(task)
        return await asyncio.gather(*tasks)

if __name__ == '__main__':
    asyncio.run(fetch_all())

Use queue to streamline the work

This is my suggestion how to use asyncio.Queue to pass URLs to worker tasks. The queue is filled as-needed, there is no pre-made list of URLs.

It takes only 30 MB RAM :)

import asyncio
from aiohttp import ClientSession

MAX_SIM_CONNS = 50
LAST_ID = 10**6

async def fetch(url, session):
    async with session.get(url) as response:
        return await response.read()

async def fetch_worker(url_queue):
    async with ClientSession() as session:
        while True:
            url = await url_queue.get()
            try:
                if url is None:
                    # all work is done
                    return
                response = await fetch(url, session)
                # ...do something with the response
            finally:
                url_queue.task_done()
                # calling task_done() is necessary for the url_queue.join() to work correctly

async def fetch_all():
    url = "http://localhost:8080/?id={}"
    url_queue = asyncio.Queue(maxsize=100)
    worker_tasks = []
    for i in range(MAX_SIM_CONNS):
        wt = asyncio.create_task(fetch_worker(url_queue))
        worker_tasks.append(wt)
    for i in range(1, LAST_ID + 1):
        await url_queue.put(url.format(i))
    for i in range(MAX_SIM_CONNS):
        # tell the workers that the work is done
        await url_queue.put(None)
    await url_queue.join()
    await asyncio.gather(*worker_tasks)

if __name__ == '__main__':
    asyncio.run(fetch_all())