A Correctness Condition for High-Performance Multiprocessors

Hybrid consistency, a consistency condition for shared memory multiprocessors, attempts to capture the guarantees provided by contemporary high-performance architectures. It combines the expressiveness of strong consistency conditions (e.g., sequential consistency, linearizability) and the efficiency of weak consistency conditions (e.g., pipelined RAM, causal memory). Memory access operations are classified as either strong or weak. A global ordering of strong operations at different processes is guaranteed, but there is very little guarantee on the ordering of weak operations at different processes, except for what is implied by their interleaving with the strong operations. A formal and precise definition of this condition is given and an algorithm for providing hybrid consistency on distributed memory machines is presented. The response time of the algorithm is proved to be within a constant multiplicative factor of the (theoretical) optimal time bounds.