Independent global snapshots in large distributed systems

Distributed systems depend on consistent global snapshots for process recovery and garbage collection activity. We provide exact conditions for an arbitrary checkpoint based on independent dependency tracking within clusters of nodes. The method permits nodes (within clusters) to independently compute dependency information based on available (local) information. The existing models of global snapshot computations provide the necessary and sufficient conditions. But, these require expensive global computations. The proposed computations can be performed by a node to identify existing global checkpoints. The nodes can also compute conditions to make a checkpoint, or conditions, such that a collection of checkpoints, can belong to a global snapshot