Propagation of authorizations in distributed database systems

摘要

We consider the propagation of authorizations in distributed database systems. If no constraints are imposed on the propagation of authorization changes, then the authorization states at different sites may evolve inconsistently. A standard solution is to suppress the distributed aspect and make all changes appear as if they had occurred in some serial order at a single site, perhaps via an atomic commit protocol. However, rigid insistence on consistency may result in authorization changes being needlessly delayed, a problem exacerbated in the context of site or communication failures. We propose an optimistic authorization propagation algorithm. We specify an authorization table and a set of operations for altering the authorization table. Each site maintains a log of authorization operations. We exploit the semantics of authorization operations to avoid relying on an undo-redo mechanism for processing out of order operations. Instead we give efficient, direct algorithms to scan the log and update the authorization table. Any inconsistencies in replicas of the authorization table are transient and are eliminated by further communication between sites. We discuss pruning the authorization log.