title: what exactly 'connections' mean in heroku postgres
body: <p>I am building a website on Django hosted at Heroku. I think at the peak time about 500-600 users can use it simultaneously. I can't figure out what is the best postgres plan.
  According to this: <a href="https://elements.heroku.com/addons/heroku-postgresql#details" rel="nofollow noreferrer">https://elements.heroku.com/addons/heroku-postgresql#details</a></p>
  <p><code>heroku-postgresql:standard-0</code> has a connection limit of 120, and
  <code>heroku-postgresql:standard-2</code> has a connection limit of 400.</p>
  <p>Is it enough to have connections of 120 for about 500 users? Or it is entirely irrelevant?</p>