title: Improving aggregation for Cosmos DB with MongoDb interface
body: <p>Trying to run very basic aggregation using Mongo API</p>
  <pre><code>aggregate([{ $group: { _id: &quot;$_Client&quot;, sumQuantity: { $sum: 1 } } }])
  aggregate([{ $group: { _id: &quot;$_ShardKey&quot;, sumQuantity: { $sum: 1 } } }])
  </code></pre>
  <p>both failed with 429 error.  There is an index for Client.</p>