Sherman: A Write-Optimized Distributed B+Tree Index on Disaggregated Memory

TL;DR

Sherman is a novel distributed B+Tree index designed for disaggregated memory architectures, significantly improving write performance using RDMA hardware features and software techniques, suitable for high-throughput, low-latency database workloads.

Contribution

Sherman introduces a write-optimized distributed B+Tree that leverages RDMA features and software techniques to enhance performance without hardware modifications.

Findings

Sherman achieves an order of magnitude higher throughput.

Sherman reduces 99th percentile latency significantly.

Sherman outperforms state-of-the-art designs on write-intensive workloads.

Abstract

Memory disaggregation architecture physically separates CPU and memory into independent components, which are connected via high-speed RDMA networks, greatly improving resource utilization of databases. However, such an architecture poses unique challenges to data indexing in databases due to limited RDMA semantics and near-zero computation power at memory-side. Existing indexes supporting disaggregated memory either suffer from low write performance, or require hardware modification. This paper presents Sherman, a write-optimized distributed B+Tree index on disaggregated memory that delivers high performance with commodity RDMA NICs. Sherman combines RDMA hardware features and RDMA-friendly software techniques to boost index write performance from three angles. First, to reduce round trips, Sherman coalesces dependent RDMA commands by leveraging in-order delivery property of RDMA. Second, to accelerate concurrent accesses, Sherman introduces a hierarchical lock that exploits on-chip memory of RDMA NICs. Finally, to mitigate write amplification, Sherman tailors the data structure layout of B+Tree with a two-level version mechanism. Our evaluation shows that, Sherman is one order of magnitude faster in terms of both throughput and 99th percentile latency on typical write-intensive workloads, compared with state-of-the-art designs.