title: Why do reads in MongoDB sometimes wait for lock?
body: <p>While using db.currentOp(), I sometimes see operations like:</p>
  
  <pre><code>{
          "opid" : 1238664,
          "active" : false,
          "lockType" : "read",
          "waitingForLock" : true,
          "op" : "query",
          .....
          "desc" : "conn"
      }
  </code></pre>
  
  <p>Why does a read operation need to wait for a lock? Is there a way to tell a query to ignore any pending writes and just go ahead and read anyway?</p>