Paxos based directory updates for geo-replicated cloud storage

Abstract

Modern cloud data stores (e.g., Spanner, Cassandra) replicate data across geographically distributed data centers for availability, redundancy and optimized latencies.^ An important class of cloud data stores involves the use of directories to track the location of individual data objects. Directory-based datastores allow flexible data placement, and the ability to adapt placement in response to changing workload dynamics. However, a key challenge is maintaining and updating the directory state when replica placement changes.^ In this thesis, we present the design and implementation of a system to address the problem of correctly updating these directories. Our system is built around JPaxos, an open-sourced implementation of the Paxos consensus protocol. Using a Paxos cluster ensures our system is tolerant to failures that may occur during the update process compared to approaches that involve a single centralized coordinator.^ We instrument and evaluate our implementation on PRObE, a large scale research testbed, using DummyNet to emulate wide-area network latencies. Our results show that latencies of directory update with our system are acceptable in WAN environments.^ Our contributions include (i) the design, implementation and evaluation of a system for updating directories of geo-replicated cloud datastores; (ii) implementation experience with JPaxos; and (iii) experience with the PRObE testbed