Guaranteeing Eventual Coherency across Data Copies, in a Highly Available Peer-to-Peer Distributed File System

摘要

Peer-to-peer systems use redundant data replicas to maintain high availability and improve on user response times. The consistency and coherency of these data replicas need to be maintained over time in face of various system changes like node joins, failures and network outages. In this paper we present a robust approach to guarantee eventual coherency of replicas in a multi-location large scale peer-to-peer distributed file system. We use a combination of data pull and push mechanisms, and a last coherent time stamp on each replica. These mechanisms ensure that no user read operation ever retrieves data that is older than a configurable upper bound in time.