title: Do compound shard keys in MongoDB work similar to compound indexes?
body: <p>Suppose my collection uses a compound shard key consisting of BlockHash and BlockHeight fields.</p>
  <p>If I ran a query to look up documents for a given BLockHeight, will Mongo have to hit every shard since we did not filter by BlockHash? Does having BlockHeight in the shard key help the query at all?</p>