title: Firestore's where query - number of reads charged
body: <p>This may sound silly, but I needed to rule out the possibilities behind the document reads of my app on Firestore.
  When the where query is used using client SDK, are all the documents downloaded to the client and then filtered or they are filtered at the server and returned?
  Also, what is the case when we use where query with cloud functions?</p>
  <p>E.g.: Let's say collection posts have 1000 documents and 10 matches the criteria mentioned in the where query, how many reads I would get charged for if I use</p>
  <ol>
  <li>Client SDK 2) Cloud Functions</li>
  </ol>