title: Where the mongodb sharded collection index info stored?
body: <p>Let's suppose that a sharded collection with shard key named "skey"
  and there is another indexed but not shard key named "ikey"</p>
  
  <p>if the query like this,</p>
  
  <pre><code>db.collection.find({"ikey": "something"})
  </code></pre>
  
  <p>It will search the docs across the all shards because it is not a shard key.</p>
  
  <p>At this point, how does the mongos know it should be searched across the shards? where is that index information stored? configServer? or each sharded mongod server?</p>