This book attempts to aggregate state-of-the-art research in parallel and distributed machine learning. We believe that parallelization provides a key pathway for scaling up machine learning to large datasets and complex methods. Although large-scale machine learning has been increasingly popular in both industrial and academic research communities, there has been no singular resource covering the variety of approaches recently proposed. We did our best to assemble the most representative contemporary studies in one volume. While each contributed chapter concentrates on a distinct approach and problem, together with their references they provide a comprehensive view of the field.

We believe that the book will be useful to the broad audience of researchers, practitioners, and anyone who wants to grasp the future of machine learning. To smooth the ramp-up for beginners, the first five chapters provide introductory material on machine learning algorithms and parallel computing platforms. Although the book gets deeply technical in some parts, the reader is assumed to have only basic prior knowledge of machine learning and parallel/distributed computing, along with college-level mathematical maturity. We hope that an engineering undergraduate who is familiar with the notion of a classifier and had some exposure to threads, MPI, or MapReduce will be able to understand the majority of the book's content. We also hope that a seasoned expert will find this book full of new, interesting ideas to inspire future research in the area.

Distributed and parallel processing of very large datasets has been employed for decades in specialized, high-budget settings, such as financial and petroleum industry applications. Recent years have brought dramatic progress in usability, cost effectiveness, and diversity of parallel computing platforms, with their popularity growing for a broad set of data analysis and machine learning tasks.

The current rise in interest in scaling up machine learning applications can be partially attributed to the evolution of hardware architectures and programming frameworks that make it easy to exploit the types of parallelism realizable in many learning algorithms. A number of platforms make it convenient to implement concurrent processing of data instances or their features. This allows fairly straightforward parallelization of many learning algorithms that view input as an unordered batch of examples and aggregate isolated computations over each of them.

Increased attention to large-scale machine learning is also due to the spread of very large datasets across many modern applications. Such datasets are often accumulated on distributed storage platforms, motivating the development of learning algorithms that can be distributed appropriately. Finally, the proliferation of sensing devices that perform real-time inference based on high-dimensional, complex feature representations drives additional demand for utilizing parallelism in learning-centric applications. Examples of this trend include speech recognition and visual object detection becoming commonplace in autonomous robots and mobile devices.