The two classes of systems we consider in this paper run on a
“shared nothing” collection of computers [19]. That is, the system is deployed on a collection of independent machines, each with
local disk and local main memory, connected together on a highspeed local area network. Both systems achieve parallelism by
dividing any data set to be utilized into partitions, which are allocated to different nodes to facilitate parallel processing. In this
section, we provide an overview of how both the MR model and
traditional parallel DBMSs operate in this environment.