How does Firestore document snapshot work?

Question

when a new document is added, snapshot fetches all the documents including the new ones or only the newly added ones ? If it fetches all the documents every time then it will add to the billing cost. How to get around this problem ?

StreamBuilder(
          stream:Firestore.instance
              .collection('chat')
              .orderBy('timeStamp', descending: true).snapshots(),
          builder: (context, streamSnapshot) {}
);

Answer 1

While your snapshots() listener stays active, the server actively monitors for changes that are relevant to your listener. When there are such changes it only sends you new documents, or documents that were changed, to your client. The client then merges those updates with its local data, and presents you with a new complete QuerySnapshot.