Dynamic Quorums for DHT-based P2P Networks

Peer-to-peer systems (P2P) have become a popular technique to architect decentralized systems. However, despite its popularity most P2P systems consist in simple applications such as file sharing or chat systems. The main reason is that more complex applications require levels of consistency that nowadays are not offered by P2P systems. In this paper, we explore how to provide consistency based on distributed mutual exclusion via quorum systems in DHT-based P2P networks. Our results show that quorum systems applied directly to such networks are not scalable due to the high traffic imposed onto the underlying network. The paper introduces some design principles for both quorum systems and protocols using them that help to boost their performance. These design principles consist in dynamic and decentralized selection of quorums and in the exposition and exploitation of internals of the DHT such as the finger table. We show that by combining both design principles it is possible to minimize the number of visited sites and the latency needed to obtain a quorum