Quorum-Based Replication in Object-Based Systems
Katsuya Tanaka, K. Hasegawa, Makoto Takizawa · 2000
this paper, we propose a novel QOL (quorum-based object locking) protocol for replicated objects, which extends the quorum-based protocol [6, 7, 13] to replicas of an object supporting abstract methods. Before performing a method op t on an object o, a quorum number N of replicas of o are locked. Suppose a pair of methods op and op u are issued to replicas. If op t and op u are update methods, then "N + N u > a" must be held in the traditional quorum-based protocol. If op t is performed on one replica, say o , and op u is performed on another replica, o , then the states of the replicas o and o will be different. The replicas o and o have the same state if op t is performed on o , op u is performed on o and op t and op u are compatible. In the quorum-based protocol, there must be at least one newest replica where all write methods issued are performed. However, there can exist replicas from which the newest version can be constructed even if there is no newest replica. In order to do this, we have to identify which methods are performed on each replica. We newly propose a version vector to identify the methods performed on each replica. In the QOL protocol, fewer replicas are locked than in the quorum-based protocol or the 2PL protocol. In section 2, we extend the traditional quorum concepts to the object-based system. In section 3, we present the QOL protocol. In section 4, we evaluate the QOL protocol