title: Is RAILS_MAX_THREADS something that Puma will set and scale during build time , or should I set it?
body: <p>I know Rails 5 ships with Puma (which we're using) and will look for RAILS_MAX_THREADS as an environment variable or default to 5 threads, but I'm receiving timeout errors with the default value. I looked at my database and found its max connections is a few thousand. </p>
  
  <p>It may be silly, but is this something Puma will set automatically and scale for, depending on its settings, or do I need to explicitly set this in the environment variables? If it needs to be manually set, what would be a good value for RAILS_MAX_THREADS?</p>
  
  <p>I've found the following helpful, but I'm not fully grasping the scalability part:</p>
  
  <p><a href="https://devcenter.heroku.com/articles/deploying-rails-applications-with-the-puma-web-server" rel="noreferrer">https://devcenter.heroku.com/articles/deploying-rails-applications-with-the-puma-web-server</a>
  <a href="https://devcenter.heroku.com/articles/concurrency-and-database-connections" rel="noreferrer">https://devcenter.heroku.com/articles/concurrency-and-database-connections</a></p>