Cache-Sensitive Skip List: Efficient Range Queries on Modern CPUs

Due to ever falling prices and advancements in chip technologies, many of today’s databases can be entirely kept in main memory. However, reusing existing disk-based index structures for managing data in memory leads to suboptimal performance due to inefficient cache usage and negligence of the capabilities of modern CPUs. Accordingly, a number of main-memory optimized index structures have been proposed, yet most of them focus entirely on single-key lookups, neglecting the equally important range queries. We present Cache-Sensitive Skip Lists (CSSL) as a novel index structure that is optimized for range queries and exploits modern CPUs. CSSL is based on a cache-friendly data layout and traversal algorithm that minimizes cache misses, branch mispredictions, and allows to exploit SIMD instructions for search. In our experiments, CSSL’s range query performance surpasses all competitors significantly. Even for lookups, it is only surpassed by the recently presented ART index structure. We therefore see CSSL as a serious alternative for mixed key/range workloads on main-memory databases.