Multi-level shared state for distributed systems

As a result of advances in processor and network speeds, more and more applications can productively be spread across geographically distributed machines. In this paper we present a transparent system for memory sharing, InterWeave, developed with such applications in mind. InterWeave can accommodate hardware coherence and consistency within multiprocessors (level-1 sharing), software distributed shared memory (S-DSM) within tightly coupled clusters (level-2 sharing), and version-based coherence and consistency across the Internet (level-3 sharing). InterWeave allows processes written in multiple languages, running on heterogeneous machines, to share arbitrary typed data structures as if they resided in local memory. Application-specific knowledge of minimal coherence requirements is used to minimize communication. Consistency information is maintained in a manner that allows scaling to large amounts of shared data. In C, operations on shared data, including pointers, take precisely the same form as operations on non-shared data. We demonstrate the ease of use and efficiency of the system through an evaluation of several applications. In particular, we demonstrate that InterWeave´s support for sharing at higher (more distributed) levels does not reduce the performance of sharing at lower (more tightly coupled) levels.