Want to create a POS application

On a Point Of Sale application for table service for example, the DB would be on the cloud. How is that managed? If I have 1000 subscribers adding table orders to the DB at the same time, it will be huge and slow. Is there a way to have one DB instance for each restaurant so they will contain only records from that specific restaurant? Or when an APP is installed on the user’s device it will have a new blank instance of the database?
Thank you all for your help.