title: How to overcome mongoDB limitation on RAM
body: <p>It is my understanding that a given index/collection in mongoDB must be able to fit within the servers ram.</p>
  <blockquote>
  <p>Yes. MongoDB keeps most recently used data in RAM. If you have created indexes for your queries and your working data set fits in RAM, MongoDB serves all queries from memory.</p>
  <p>MongoDB does not cache the query results in order to return the cached results for identical queries.</p>
  </blockquote>
  <p>(<a href="https://docs.mongodb.com/v3.2/faq/fundamentals/" rel="nofollow noreferrer">source</a>)</p>
  <p>I have a collection that is well over 16gb big but only 16gb of ram on my server.  I view this server as sufficient for the modest needs of my project.  Two questions:</p>
  <ol>
  <li><p>I don't have any good reason to split my database into multiple collections--further I imagine that querying multiple collections would be extremely slow (given that mongo wants to keep the collection live in ram).  Is there any other solution?</p>
  </li>
  <li><p>Is there any database with similar user interface to mongo that does not require that I keep my database in ram?</p>
  </li>
  </ol>