title: Do deleted SQL entries still take up space/rows?
body: <p>I'm developing an app through Django, where users can update specific entries using a RESTful interface. Since everything is posted through JSON, and the number of entries can stay the same, decrease, or increase everytime a user updates their entries, I thought the best way to handle this would be to delete all of the user's current entries, and re-add all the entries they submitted. </p>
  
  <p>I'm using heroku to host the site, and for their hobby databases, they restrict by # of rows. Even for their standard Databases, they restrict based on size... I have noticed that when I delete objects in Django, the index will never reset, and I understand why, but does that mean that deleted rows still take up space/exist? I'm using PostgreSQL if that helps</p>