Distributed Transactional Memory for General Networks

We consider the problem of implementing transactional memory in large-scale distributed networked systems. We present and analyze Spiral, a novel distributed directory-based protocol for transactional memory. Spiral is designed for the data-flow distributed implementation of software transactional memory which supports three basic operations: publish, allowing a shared object to be inserted in the directory so that other nodes can find it; lookup, providing a read-only copy of the object to the requesting node; move, allowing the requesting node to write the object locally after the node gets it. The protocol runs on a hierarchical directory construction based on sparse covers, where clusters at each level are ordered to avoid race conditions while serving concurrent requests. Given a shared object the protocol maintains a directory path pointing to the object. The basic idea is to use “spiral” paths that grow outward to search for the directory path of the object in a bottom-up fashion. For general networks, this protocol guarantees an O(log² n · log D) approximation for move requests, where n is the number of nodes and D is the diameter of the network. It also guarantees polylog approximation for lookup requests. To the best of our knowledge, this is the first consistency protocol for distributed transactional memory that achieves poly-log approximation in general networks.