Bad Django / uwsgi performance

Question

I am running a django app with nginx & uwsgi. Here\'s how i run uwsgi:

sudo uwsgi -b 25000 --chdir=/www/python/apps/pyapp --module=wsgi:application --env DJA         


        

Answer 1

Please run benchmarks much longer than a minute (5-10 at least), You really won't get much information from such a short test. And use uWSGI's carbon plugin to push stats to carbon/graphite server (You will need to have one), You will have much more information for debugging.

When You send 500 concurrent requests to Your app and it can't handle such load, listen queue on each backend will be filled pretty quickly (it's 100 requests by default), You might want to increase that, but if workers can't process requests that fast and listen queue (also known as backlog) is full, linux network stack will drop request and You will start getting errors.

Your first benchmark states that You can process single request in ~42 ms, so single worker could process at most 1000ms / 42ms = ~23 requests per second (if db and other parts of app stack didn't slow down as concurrency goes up). So to process 500 concurrent requests You would need at least 500 / 23 = 21 workers (but in reality I would say at least 40), You have only 16, no wonder it breaks under such load.

EDIT: I've mixed rate with concurrency - at least 21 workers will allow You to process 500 requests per second, not 500 concurrent requests. If You really want to handle 500 concurrent requests than You simply need 500 workers. Unless You will run Your app in async mode, check "Gevent" section in uWSGI docs.

PS. uWSGI comes with great load balancer with backend autoconfiguration (read docs under "Subscription Server" and "FastRouter"). You can setup it in a way that allows You to hot-plug new backend as needed, You just start workers on new node and they will subscribe to FastRouter and start getting requests. This is the best way to scale horizontally. And with backends on AWS You can automate this so that new backends will be started quickly when needed.