Not to mention the algorithms and business behind which ad to serve where and when are worthy of an entire field of study all by themselves. Read the Advertisi

Not to mention the algorithms and business behind which ad to serve where and when are worthy of an entire field of study all by themselves. Read the Advertising chapter in Mining Massive Datasets - http://www.mmds.org/ http://www.mmds.org/ - and then figure out how you'd tackle those problems when you distribute them onto other people's servers.