A dynamic coherence protocol for distributed shared memory enforcing high data availability at low costs

DSM coherence protocols should scale well for large networks. Fault-tolerance in terms of highly available data access and uninterrupted DSM service is needed in large-scale environments that have a greater number of potentially malfunctioning components. We present a new class of dynamic coherence protocols for DSM systems in error-prone networks whose instances offer highly available access to DSM data at low operation costs. The approach is based on the highly scalable Boundary-Restricted (BR) coherence protocol class. The new protocol class, called the Dynamic Boundary-Restricted (DBR) coherence protocol class, maintains read/write frequencies of DSM requests at run-time. This information is used to dynamically adjust the minimum number of cached copies of a single DSM page in order to guarantee a given degree of data availability. The description of the new protocol class is accompanied by an analysis covering a large variety of workloads. This analysis presents the overall savings achieved by using a DBR coherence protocol in comparison to a static BR protocol.