MapReduce is about hiding explicit parallel primitives like threads and MPI from users (programmers): You only need to implement two functions map and reduce in

MapReduce is about hiding explicit parallel primitives like threads and MPI from users (programmers): You only need to implement two functions map and reduce in a typical framework. Yes, you can certainly implement MapReduce with MPI partially, but typical MapReduce framework like Hadoop also handles fault tolerance transparently to users.