MapReduce has been gaining much attention in data intensive computing field. As you know, it is well known as a very popular framework for batch-processing.
Recently, however, Tyson Condie who is a Ph.D student in UC Berkeley accomplishes MapReduce Online. Today, I heard this news from Data Beta. Actually, It is amazing works since the original MapReduce is specialized and designed for only batch-processing. In addition, most people believe that MapReduce will remain a batch-processing.
The essential of MapReduce online is that it tries to hold the fault-tolerance model of the original MapReduce, whereas it provides the the pipelining of results across tasks and jobs instead of materializing the output of each MapReduce task and job into disk. Consequently, MapReduce online enables the program to return the result earlier from a big job.
You can get further information from MapReduce Online.