So, I'm brainstorming up a recommended-item algorithm, and I like Amazon's. It has "Customers who bought this also bought" and "related" recommended sections. I'm guessing the former is based on sales data, and the other is based on catalog data, such as category, attributes, etc.
Does anyone know how Amazon or other similar large retail companies pull these recommended products onto their product pages? Is it done on the fly or done at certain intervals? I can't decide which way it should be done at this time. I'm leaning toward the latter, because the algorithm can be more intricate, but I'm guessing this will need to be processed and updated at certain interval to minimize page load times.
Any comments from programmer who have worked on this type of project are welcome!