title: Mongodb background indexes - are they still background once created?
body: <p>When creating an index in mongodb, you can specify the <code>background: true</code> flag, which causes the index creation to be non-blocking.  This is great in production since you don't want the whole database locked up while creating an index that you clearly didn't critically need before (since you didn't have it).</p>
  
  <p>Reading the <a href="http://docs.mongodb.org/manual/core/indexes/">docs</a>, it seems like this flag only determines how the index is created, and once it's done being built the index acts exactly like a normal index.  Which is what I'd want -- I wouldn't want the index to get out of sync with docs because it's being updated in the background, although I can imagine a database that does this.</p>
  
  <p>I'm asking here because the <code>getIndexes</code> command shows that the index is still marked as <code>background</code> even after it's created.  Is this just a reminder about how it was created?  Or do <code>background</code> indexes behave differently after being created?  Maybe some subtlety with replication?</p>