VELOS: a new approach for efficiently achieving high availability in partitioned distributed systems

Abstract

The work presents a new protocol, VELOS, for tolerating partitionings in distributed systems with replicated data. Our primary goals were influenced by efficiency and availability constraints. The proposed protocol achieves optimal availability, according to a well known metric, while ensuring one copy serializability. In addition, however, VELOS is designed to reduce the cost involved in achieving high availability. We have developed mechanisms through which transactions, in the absence of failures, can access replicated data objects and observe shorter delays than related protocols, and impose smaller loads on the network and the servers. Furthermore, VELOS offers high availability without relying on system transactions that must execute to restore availability when failures and recoveries occur. Such system transactions typically access all (replicas of all) data objects and thus introduce significant delays to user transactions and consume large quantities of resources such as network bandwidth and CPU cycles. Thus, we offer our protocol as a proof that high availability can be achieved inexpensively.