A Survey on Distributed Hash Table (DHT): Theory, Platforms, and Applications

Distributed Hash Table (DHT) plays an important role in distributed systems and applications, especially in large-scale distributed environments. In normal Client/Server model (C/S model) since most of the resources is centralized at server, it becomes the most important part as well as the bottleneck and weak point of the system. On the contrary, distributed model (a typical one is peer-to-peer (P2P) model) distributes the resources on the nodes in the system. This model requires that utilizing all the peers’ capability efficiently and providing better robustness. Luckily DHT technology meets the requirements so that it promotes the development of P2P greatly. DHT organizes the distributed resources so well that peers only need to know part of the system they can get resources efficiently. DHT only has two basic operations: get data from DHT and put data into DHT, which is so simple and graceful, but is suitable for a great variety of applications, and provides good robustness and high efficiency, especially in large-scale systems. For decades extensive work has been done for DHT. In academia, researchers have proposed several variants of DHT and improvements, which manage the resources in many kinds of structures, providing abundant choices for the construction of distributed system. Meanwhile, many platforms of DHT is constructed, which can be regarded as a bridge translating DHT from theory to practice and solve many practical problems such as load balance, multiple replicas, consistency, latency and so on. Furthermore, lots of applications based on DHT are proposed such as such as multicast, anycast, distributed file systems, search, storage, content delivery network, file sharing and communication. There are also some surveys about DHT, but most of them only focus on the theory. Plenty of DHT platforms and applications are ignored. The objective of this book is to summarize the development of DHT in both academic and industrial fields. It covers the main theory, platforms and applications of DHT. From this book, readers could learn the principle of several popular DHT structures, many platforms used in both academic and commercial fields, and a wide range of applications DHT can be deployed. Meanwhile, some limitations and week points of DHT are proposed at last. This book includes five chapters. In Chapter 1 some background information about DHT is introduced. Seven variants of DHT are studied and compared in many aspects in Chapter 2, which is the base of the platforms. In Chapter 3 two kinds of platforms (academic and open-source platform and commercial platform) containing fifteen different platforms are analyzed, based on which applications can be constructed. In Chapter 4 eight kinds of applications are introduced, and the advantages of DHT in these applications are analyzed. Chapter 5 summarizes the power of DHT, and analyzes the limitation of DHT.