SmartMerge: A new approach to reconfiguration for atomic storage

Abstract

In this paper, we study reconfiguration mechanisms for atomic storage systems. We observe that the state of the art approach for reconfiguration in an asynchronous environment has several disadvantages compared to the classical consensus-based approach, which requires eventual synchrony. For example, an unfortunate combination of remove operations may lead to a configuration with too few or even no processes. We present SmartMerge, a novel approach that provides most of the benefits of consensus-based reconfiguration, yet can be implemented in a fully asynchronous system. SmartMerge utilizes a merge function to aptly combine concurrently issued changes to both the set of processes and the quorum system of the storage. The approach is general and can use any suitable function. In addition to the expressive reconfiguration policies enabled by SmartMerge, our atomic storage also has improved efficiency: Every reconfiguration imposes only a constant overhead on concurrent read and write operations.