Application-independent reconciliation for nomadic applications

Abstract

We describe attempts to build an application-independent model to support reconciliation of diverged replicas of shared objects. While replicas are disconnected from one another, actions on the shared objects are recorded in a log. An action is composed of a precondition, an operation and a postcondition. When reconnecting, the system attempts to reconcile the divergent replicas, in several phases. A symbolic phase merges the separate logs, creating one or more schedules, such that preconditions from one log remain true despite the postconditions introduced by the other. Then, a simulation phase checks the possible outcomes by actually applying the schedules to scratch copies of the shared objects. Finally, a selection phase allows users or applications to select one of the candidate schedules.Our approach supports sharing general objects, where one update may reference multiple objects (not just a single file or database). Compared to previous work on log-based reconciliation, our logs capture more semantic information and provide the application with more powerful and finer control over the outcome of reconciliation.