Maintaining replicated authorizations in distributed database systems

We consider the propagation of authorizations in distributed database systems. We present an optimistic replica control algorithm that ensures that the authorization table at any given site evolves consistently with respect to other sites. The motivation for using optimistic replica control to maintain authorizations is that site and communication failures do not needlessly delay authorization changes. In addition, the semantics of the authorization operations we employ can be exploited to resolve transient inconsistencies without the expense of an undo-redo mechanism. Instead, we give efficient, direct algorithms whereby a site scans its log of authorization requests and updates its authorization table correspondingly. From the system perspective, any inconsistencies in the authorization table replicas maintained at different sites are transient and are eliminated by further communication. We show how a site can prune its authorization log by the use of a matrix that records how current remaining sites in the system are.