Commutativity Based Concurrency Control and Recovery for Multiversion Objects

Atomic objects have suitable properties to realize reliable distributed computing. Using semantic information of atomic objects can make reliable distributed computing highly concurrent. This paper describes a commutativity based concurrency control algorithm in a multiversion object for highly concurrent distributed computing. Weihl proposed two concurrency control algorithms based on a commutative relation: a forward commutativity and a backward commutativity. However, each commutativity relation is not a subset of another one so that we cannot say which algorithm is better. The advantage of the algorithms depends on application programs. Moreover, each algorithm requires a different recovery algorithm and a different implementation of an object. Using multiversion objects makes it possible to combine the two algorithms because multiversion objects enable atomic actions to access both committed states and current states of objects at the same time. We call our commutative relation a general commutative relation. The two commutative relations are not subsets of each other, but a general commutative relation includes both commutative relations completely. The fact means that a general commutative relation can achieve a higher degree of concurrency. [email protected], [email protected]