Message-optimal incremental snapshots

The problem of obtaining a global state or snapshot of a distributed processing system is considered. A message-efficient protocol is presented for obtaining incremental snapshots. First, worst-case lower bounds on the number of messages used by any protocol that solves the incremental snapshot problem are given, and then a protocol that is message-efficient is provided. This protocol obtains a snapshot of the system using the most recent snapshot. The message complexity of the incremental snapshot protocol matches the two lower bounds simultaneously, and hence the protocol is asymptotically message optimal. For applications in database systems, debugging distributed programs, monitoring events, or checkpointing, the protocol is asymptotically message optimal. Because of its simplicity, the protocol can be used readily, and since it uses the minimum number of additional messages, the throughput of the distributed system is not adversely affected.<>