Hadoop MapReduce is a batch-processing system. Why? Because that’s the way Google described their MapReduce implementation.
But it doesn’t have to be that way. Introducing HOP: the Hadoop Online Prototype [updated link to final NSDI ’10 version]. With modest changes to the structure of Hadoop, we were able to convert it from a batch-processing system to an interactive, online system that can provide features like “early returns” from big jobs, and continuous data stream processing, while preserving the simple MapReduce programming and fault tolerance models popularized by Google and Hadoop. And by the way, it exposes pipeline parallelism that can even make batch jobs finish faster. This is a project led by Tyson Condie, in collaboration with folks at Berkeley and Yahoo! Research.