the entire point was that it's not mapreduce, it's a stream processing system. try <a href="http://wiki.s4.io/Manual/S4Overview#toc1" rel="nofollow">http://wiki.s4.io/Manual/S4Overview#toc1</a> for a "<i>what is S4</i>" intro.<p><i>The architecture resembles the Actors model, providing semantics of encapsulation and location transparency, thus allowing applications to be massively concurrent while exposing a simple programming interface to application developers.</i><p>and<p><i>S4 is a general-purpose, distributed, scalable, partially fault-tolerant, pluggable platform that allows programmers to easily develop applications for processing continuous unbounded streams of data.</i><p>go stream processing. also see <i>Flume</i> for related recent works.