Worker Dynos, Background Jobs and Queueing
Background jobs are key to building truly scalable web apps as they transfer both time and computationally intensive tasks from the web layer to a background process outside the user request/response lifecycle. This ensures that web requests can always return immediately and reduces compounding performance issues that occur when requests become backlogged.
A good rule of thumb is to avoid web requests which run longer than 500ms. If you find that your app has requests that take one, two, or more seconds to complete, then you should consider using a background job instead.