A log(n) multi-mode locking protocol for distributed systems

Abstract

Trends in high-end clusters are to deploy an ever larger number of processors to push the envelope on parallelizing scientific applications. A similar trend exists in server computing where more and more servers are composed into a farm. One of the main challenges in such environments is to achieve scalability of synchronization, specifically for locking. Our work focuses on scalable locking in distributed systems. At its essence is a peer-to-peer protocol for multi-mode hierarchical locking, which is applicable to transaction-style processing and distributed agreement. We demonstrate high scalability combined with low response times in high-performance cluster environments. Our experiments on an IBM SP show that the number of messages approaches an asymptote at 15 nodes, from which point on the message overhead is in the order of 3-9 messages per request, depending on system parameters. At the same time, response times increase linearly with a proportional increase in requests and, consequently, higher concurrency levels. We observed response times under 2 and 10 msec for up to 25 and 80 nodes for critical sections that are one 25th the size of non-critical code. Our approach benefits in large from high levels of concurrency upon resolving requests and dynamic path compression for request propagation. Besides its technical strengths, our approach is intriguing due to its simplicity and its wide applicability, ranging from large-scale clusters to server-style computing.