Nathan Marz writes on Big Data Lambda Architecture, promoting his upcoming book from Manning, Big Data. It's a comprehensible take on big data architectures. (See Chapter 1 [pdf].)
In a nutshell:
Computing arbitrary functions on an arbitrary dataset in real time is a daunting problem. There is no single tool that provides a complete solution. Instead, you have to use a variety of tools and techniques to build a complete Big Data system.
The lambda architecture solves the problem of computing arbitrary functions on arbitrary data in real time by decomposing the problem into three layers: the batch layer, the serving layer, and the speed layer.
