Link Lifetimes and Randomized Neighbor Selection in DHTs

Several models of user churn, resilience, and link lifetime have recently appeared in the literature [12], [13], [34], [35]; 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 user 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, 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 [8], our results show that deterministic networks (e.g., Chord [28], CAN [24]) 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 users in such systems should prefer neighbors with smaller zones rather than larger age as suggested in prior work [13], [30]. We finish the paper by demonstrating the effectiveness of the proposed min-zone neighbor selection for heavy-tailed user lifetime distributions with the shape parameter alpha obtained from recent measurements [4], [31].