title: Search for a unique username using firestore and Flutter efficiency
body: <p>I used Firebase cloud-firestore to check if the username is unique or exists in firestore cloud using this code and it work correctly until now,but What happened if I have more than 10000 username to check using this code ?</p>
  
  <p>So How much time need to check the database ? and Do you suggest using algolia or elasticSearch instead . </p>
  
  <pre><code>    final QuerySnapshot result = await Future.value(Firestore.instance
          .collection('check_username')
          .where('username', isEqualTo: userNameController.text.toLowerCase())
          .limit(1)
          .getDocuments());
      final List&lt;DocumentSnapshot&gt; documents = result.documents;
      if (documents.length == 1) {
        print("UserName Already Exits");
        setState(() {
          _userExist = documents.length == 1;
        });
      } else {
        print("UserName is Available");
        setState(() {
          _userExist = documents.length == 1;
        });
      }```
  </code></pre>