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Transparent Recovery of Mach Applications

We have built a software layer on top of Mach 2.5 that recovers multitask Mach applications from fail-stop failures. The layer implements Optimistic Recovery (OR), a mechanism for transparent recovery from failing tasks and processors, based on asynchronous checkpointing and logging of inter{task messages. OR recovers from failure by restoring a checkpoint and replaying the logged messages. The current prototype supports message communication via sends and receives, simple port operations, and task interactions through the environment manager. This paper discusses the issues Mach raised for this implementation, the structure of the OR layer, the design of future enhancements, and comparisons with other recovery techniques.