最小化Firebase的下载

Question

在我的应用程序的NotificationListener中，我正在监听（并与我的SQLite同步）从Firebase获取新数据或更改的数据。 在第一种情况下，我想检查借出书籍的状态是否已经改变。因此，我在onStartCommand中使用以下代码：

    databaseLoanedBooks.orderByChild("contactId").equalTo(firebase_uid).addChildEventListener(new ChildEventListener() {
        @Override
        public void onChildAdded(DataSnapshot dataSnapshot, String s) {
        }    
        @Override
        public void onChildChanged(DataSnapshot dataSnapshot, String s) {
            String book_id = dataSnapshot.child("bookId").getValue(String.class);
            String book_status = dataSnapshot.child("bookStatus").getValue(String.class);
            DatabaseHelper db = new DatabaseHelper(getApplicationContext());
            List<String> all_book_ids = db.getAllBookIds();
            if (all_book_ids.contains(book_id)){
                // some action... check for status, if status=x output of notification
            } 
        }
        @Override
        public void onChildRemoved(DataSnapshot dataSnapshot) {
        }
        @Override
        public void onChildMoved(DataSnapshot dataSnapshot, String s) {
        }
        @Override
        public void onCancelled(DatabaseError databaseError) {
        }
    });

此外，我想检查服务器上是否有关于借出书籍的新消息。因此，我在NotifiactionListener的onStartCommand中使用以下代码：

    final List<String> all_book_ids = db.getAllBookIds();
// iterate through all book-ids the user has loaned at the moment (and saved in SQL)
        for (int i = 0; i < all_book_ids .size(); i++) {
            final String check_book_id = all_book_ids.get(i);
            databaseMessage.child(check_book_id).addChildEventListener(new ChildEventListener() {
                @Override
                public void onChildAdded(DataSnapshot dataSnapshot, String s) {
                    ChatMessage chatMessage = dataSnapshot.getValue(ChatMessage.class);
                    String message_id = dataSnapshot.child("messageId").getValue(String.class);
                    String message_book_id = dataSnapshot.child("messageBookId").getValue(String.class);
                    String message_uid = dataSnapshot.child("messageUid").getValue(String.class);
                    String message_text = dataSnapshot.child("messageText").getValue(String.class);
                    String message_time = String.valueOf(chatMessage.getMessageTime());
                    DatabaseHelper db = new DatabaseHelper(getApplicationContext());
                    final List<String> all_message_ids = db.getAllMessagesIds();
                    final List<String> all_book_ids = db.getAllBookIds();
                    String new_message = getString(R.string.text_new_message);
                    if (all_book_ids.contains(message_book_id)) {
                        if (all_message_ids.contains(message_id_changed)) {
                            // already exists
                        } else {
                            ContentValues values_new = new ContentValues();
                            values_new.put(DatabaseHelper.COLUMN_CHAT_FCM_ID, message_id);                                values_new.put(DatabaseHelper.COLUMN_CHAT_BOOK_ID, message_book_id);
                            values_new.put(DatabaseHelper.COLUMN_CHAT_TEXT, message_text_changed);                                values_new.put(DatabaseHelper.COLUMN_CHAT_BOOK_ID, message_uid);
                            values_new.put(DatabaseHelper.COLUMN_CHAT_TIME, message_time);
                            todoUri = getContentResolver().insert(DataContentProvider.CONTENT_URI_CHATS, values_new);
                            HashMap<String, String> user_session = session.getUserDetails();
                            // UID from sharedpreferences
                            String noti_status = user_session.get(SessionManager.KEY_NOTIFICATION);

                                String user_name_chat_sql = String.valueOf(db.getContactName(message_uid));
                                String book_name = String.valueOf(db.getBookNameForWA(message_book_id));
                                user_name_chat_sql = user_name_chat_sql.replaceAll("\\p{P}", "");
                                book_name = book_name.replaceAll("\\p{P}", "");
                                showNotificationNewMessage(new_message, user_name_chat_sql, message_text, book_name);                               
                        }
                    }
                }
                @Override
                public void onChildChanged(DataSnapshot dataSnapshot, String s) {
                }
                @Override
                public void onChildRemoved(DataSnapshot dataSnapshot) {
                }
                @Override
                public void onChildMoved(DataSnapshot dataSnapshot, String s) {
                }
                @Override
                public void onCancelled(DatabaseError databaseError) {
                }
            });
        }

使用此代码，每个用户每天的数据使用量约为2 MB。所以我的问题是：如何最大限度地减少我的下载并遵循我的数据使用情况？在检查新消息的代码中，我尝试使用for循环来限制收集的数据仅针对相应用户的书籍，但遗憾的是这不是解决方案。我该如何解决这个问题？