Is doing asynchronous database calls in a flask application possible?
It sounds like the issue isn’t the Flask application itself but rather your WSGI server. Flask is designed to handle one request at a time. To serve the app so that multiple people can hit it simultaneously, you should configure the WSGI server to use more workers. If a request hits the server while your long process is running, a worker will generate a new instance of the app and serve the request. This is easy to set up in IIS.
Of course, if you have four workers and then four clients run the long function simultaneously then you’re back in this situation. If that will happen frequently you can assign more workers or move to a different WSGI framework that supports async like Quart or Sanic.
The approach you’ve outlined above should speed up the execution of the long process, though. But Flask itself is not designed to await. It holds the thread until it’s finished.
More details in this answer: https://stackoverflow.com/a/19411051/5093960