Coherence in Distributed Persistent Object Systems

Distributed system builders are faced with the task of meeting a variety of requirements on the global behaviour of the target system, such as stability, fault-tolerance and failure recovery, concurrency control, commitment, and consistency of replicated data. Coherence means satisfying these types of requirements, although the subset may vary from system from to system. This paper describes an approach to coherence enforcement in distributed persistent object systems based upon system-wide backtracking. The approach is optimistic in the sense that violations of coherence are resolved rather than prevented—backtracking is the agent of this resolution. The coherence support is realised as a transaction service, supported by the backtrack capability.