Data Engineering

Abstract

A quorum system is a collection of subsets of servers, every two of which intersect. Quorum systems have been suggested as a tool for concurrency control in replicated databases almost twenty years ago. They promised to guarantee strict consistency and to provide high availability and fault-tolerance in the face of server crashes and network partitions. Despite these promises, current commercial replicated databases typically do not use quorum systems. Instead they use mechanisms which guarantee much weaker consistency, if any. Moreover, the interest in quorum systems seems to be waning even in the database research community. This paper attempts to explain why quorum systems have not fulfilled their old promises, and at the same time to argue why the current state of affairs may change. As technological advances bring new capabilities, and new applications bring new requirements, the time may have come to review the validity of some long standing criticisms of quorum systems. Anothe..