cooking ribs for restaurant

How do chefs cook bbq ribs at a restaurant if they want to cook them for 6 to10 hrs. How do they know how many to cook at one time. I am planning to start my own pit bbq but this question has always got me stumped. What if I start by cooking 20 racks of ribs and only sell 10? Can I keep them in a cooler for the next day? If my hours are 11 am to 8 pm how do I keep the ribs that have been cooked in the morning until that evening?

                                                      Thanks Zimbie9