Splaying Log-Structured Merge-Trees

Abstract

Modern persistent key-value stores typically use a log-structured merge-tree (LSM-tree) design, which allows for high write throughput. Our observation is that the LSM-tree, however, has suboptimal performance during read-intensive workload windows with non-uniform key access distributions. To address this shortcoming, we propose and analyze a simple decision scheme that can be added to any LSM-based key-value store and dramatically reduce the number of disk I/Os for these classes of workloads. The key insight is that copying a frequently accessed key to the top of an LSM-tree ("splaying'') allows cheaper reads on that key in the near future.