title: When I have to query Apple's Feedback Service
body: <p>One thing I haven't found is <strong>when</strong> to call the Apple's Feedback Service for push notifications. The <a href="http://developer.apple.com/library/ios/#documentation/NetworkingInternet/Conceptual/RemoteNotificationsPG/Introduction/Introduction.html#//apple_ref/doc/uid/TP40008194-CH1-SW1" rel="nofollow">Local and Push Notification Programming Guide</a> says:</p>
  
  <blockquote>
    <p>Providers <strong>should periodically query</strong> the feedback service to get the list of device tokens for their applications, each of which is identified by its topic. Then, after verifying that the application hasn’t recently been re-registered on the identified devices, a provider should stop sending notifications to these devices.</p>
  </blockquote>
  
  <p>But is there a best practice to follow? E.g.:</p>
  
  <ol>
  <li>Everyone calls it <em>before sending any notification</em>, or</li>
  <li>Everyone calls it <em>once a day</em>, or</li>
  <li>Everyone calls it <em>once a week</em>, or</li>
  <li>...</li>
  </ol>