title: choosing a mongodb sharding key
body: <p>I am launching a data storage service for my application.  MongoDB 
  is running as the storage mechanism, and I have created 2 shards to 
  start.</p>
  
  <p>The application will be storing event data, and all data will be 
  structured as follows:</p>
  
  <pre><code>{ 
    _id: '4fa2f7e25626cd1374000002', 
    created_at: '2012-05-03T21:25:54 00:00', 
    name: 'client_session_connect', 
    session_remote_id: '74ACF9AA-9E09-11E1-8C9E-8462380DA5E6', 
    zone_id: '74ACF9AA-9E09-11E1-8C9E-1231380DA5E6',
    additional: {
      some_other_key: 'value'
    }
  } 
  </code></pre>
  
  <p>Events will have a variety of names, and any new event can be created 
  at any time with a new event name.  There will be plenty of events in 
  the system with the same name.  _id, created_at, and name will be part 
  of every event, but no other values are guaranteed. </p>
  
  <p>Based on what I have read (<a href="http://www.mongodb.org/display/DOCS/Choosing+a+Shard+Key" rel="nofollow noreferrer">here</a>, and <a href="https://rads.stackoverflow.com/amzn/click/com/1449303218" rel="nofollow noreferrer" rel="nofollow noreferrer">here</a>), it seems that the best sharding key would 
  be { name: 1, created_at: 1 }.  Would I be correct in this 
  interpretation?</p>