Towards a Universal Approach for Monotonic Searchability in Self-Stabilizing Overlay Networks

摘要

For overlay networks, the ability to recover from a variety of problems likemembership changes or faults is a key element to preserve their functionality.In recent years, various self-stabilizing overlay networks have been proposedthat have the advantage of being able to recover from any illegal state.However, the vast majority of these networks cannot give any guarantees on itsfunctionality while the recovery process is going on. We are especiallyinterested in searchability, i.e., the functionality that search messages for aspecific identifier are answered successfully if a node with that identifierexists in the network. We investigate overlay networks that are not onlyself-stabilizing but that also ensure that monotonic searchability ismaintained while the recovery process is going on, as long as there are nocorrupted messages in the system. More precisely, once a search message fromnode $u$ to another node $v$ is successfully delivered, all future searchmessages from $u$ to $v$ succeed as well. Monotonic searchability was recentlyintroduced in OPODIS 2015, in which the authors provide a solution for a simpleline topology. We present the first universal approach to maintain monotonic searchabilitythat is applicable to a wide range of topologies. As the base for our approach,we introduce a set of primitives for manipulating overlay networks that allowsus to maintain searchability and show how existing protocols can be transformedto use theses primitives. We complement this result with a generic search protocol that together withthe use of our primitives guarantees monotonic searchability. As an additional feature, searching existing nodes with the generic searchprotocol is as fast as searching a node with any other fixed routing protocolonce the topology has stabilized.