What db does the new enterprise use - airbnb, tesla, uber... even google, apple, facebook, amazon? If "software is eating the world", and the new enterprises a

What db does the new enterprise use - airbnb, tesla, uber... even google, apple, facebook, amazon? If "software is eating the world", and the new enterprises are software companies (even if they don't sell software), do they write their own custom solution, optimized for their usage patterns? Or do they "grow up" into traditional companies, and rely on outside vendors for their software? I don't think so.