A New Look at the Roles of Spinning and Blocking

Database engines face growing scalability challenges as core counts exponentially increase each processor generation, and the efficiency of synchronization primitives used to protect internal data structures is a crucial factor in overall database performance. The trade-offs between different implementation approaches for these primitives shift significantly with increasing degrees of available hardware parallelism. Blocking synchronization, which has long been the favored approach in database systems, becomes increasingly unattractive as growing core counts expose its bottlenecks. Spinning implementations improve peak system throughput by a factor of 2x or more for 64 hardware contexts, but suffer from poor performance under load. In this paper we analyze the shifting trade-off between spinning and blocking synchronization, and observe that the trade-off can be simplified by isolating the load control aspects of contention management and treating the two problems separately: spinning-based contention management and blocking-based load control. We then present a proof of concept implementation that, for high concurrency, matches or exceeds the performance of both user-level spinlocks and the pthread mutex under a wide range of load factors.