Analysis of Link Lifetimes and Neighbor Selection in Switching DHTs

Several models of user churn, resilience, and link lifetime have recently appeared in the literature; however, these results do not directly apply to classical Distributed Hash Tables (DHTs) in which neighbor replacement occurs not only when current users die, but also when new users arrive into the system, and where replacement choices are often restricted to the successor of the failed zone in the DHT space. To understand neighbor churn in such networks, which we call switching DHTs, this paper proposes a simple, yet accurate, model for capturing link dynamics in structured P2P systems and obtains the distribution of link lifetimes for fairly generic DHTs. Similar to, our results show that deterministic networks (e.g., Chord, CAN) unfortunately do not extract much benefit from heavy-tailed user lifetimes since link durations are dominated by small remaining lifetimes of newly arriving users that replace the more reliable existing neighbors. We also examine link lifetimes in randomized DHTs equipped with multiple choices for each link and show that selecting the best neighbor in these scenarios is rather complicated as it depends on the desired load balancing, link resilience, and overhead. We offer insight into the various selection algorithms, their performance, and possibilities for improvement.