Large-scale data analysis has become increasingly impor-
tant for many enterprises. Recently, a new distributed com-
puting paradigm, called MapReduce, and its open source
implementation Hadoop, has been widely adopted due to
its impressive scalability and flexibility to handle structured
as well as unstructured data. In this paper, we describe
our data warehouse system, called Cheetah, built on top of
MapReduce. Cheetah is designed specifically for our online
advertising application to allow various simplifications and
custom optimizations. First, we take a fresh look at the data