title: Mongoose Connection Pool
body: <p>I noticed in the Mongoose docs that there is support for a connection pool.</p>
  
  <p><a href="http://mongoosejs.com/docs/connections.html" rel="noreferrer">http://mongoosejs.com/docs/connections.html</a></p>
  
  <p>Considering that node is single threaded why is there a connection pool? 
  What's the lifecycle of connections in the pool?</p>