Consistency issues in distributed checkpoints
A global checkpoint is a set of local checkpoints, one per process. The traditional consistency criterion for global checkpoints states that a global checkpoint is consistent if it does not include messages received and not sent. This paper investigates other consistency criteria, transitlessness, and strong consistency. A global checkpoint is transitless if it does not exhibit messages sent and nor received. Transitlessness can be seen as a dual of traditional consistency. Strong consistency is the addition of transitlessness to traditional consistency. The main result of this paper is a statement of the necessary and sufficient condition answering the following question: "Given an arbitrary set of local checkpoints, can this set be extended to a global checkpoint that satisfies P-m (where LP is traditional consistency, transitlessness, or strong consistency). From a practical point of view, this condition, when applied to transitlessness, is particularly interesting as it helps characterize which messages do not need to be recorded by checkpointing protocols.
consistency checkpointing transitlessness strong consistency distributed systems fault-tolerance rollback recovery