基于LSM树的键值存储系统技术研究综述

Key Value Storage Technology Based on LSM-tree:A Survey

键值存储是数据库最简单的组织形式。在数据密集型的应用场景中,键值存储系统发挥着关键的作用。随着对及时数据分析需求的增加,良好的系统性能变得越来越重要。目前大多数键值存储系统的存储引擎都是日志结构合并树(Log-Structured Merge Tree, LSM树)。因具有卓越的写性能,LSM树被广泛应用于写密集型的场景和现代NoSQL系统的存储层。与传统的B树相比,LSM树采用顺序写入的访问模式,并使用内存缓冲区来批处理新的写入线程,因此LSM树具有更大的写优势。然而,数据的重复读写和不必要的压缩操作导致了LSM树的读写放大问题,从而严重影响了系统的性能,尤其在数据密集型的应用场景。如今,研究人员做了大量工作来缓解这些问题,文中研究了影响LSM树性能的各个因素,搜集了大量提升基于LSM树的键值系统性能的文献,并对其加以整理和分类,讨论它们的优势和权衡,使读者可以了解基于LSM树的存储技术及其优化策略,最后调查了几个具有代表性的基于LSM树的键值存储技术并讨论了潜在的未来研究方向。

Key-value storage is the simplest form of database organization and it plays a key role in data-intensive application scenarios.With the increasing demand for timely data analysis,good system performance becomes more and more important.At present,the storage engine of most key-value storage systems is the log-structured merge tree(LSM-tree).Because of its excellent write performance,the LSM-tree is widely used in the write intensive scenes and the storage layer of modern NoSQL system.Compared to the traditional B-tree,LSM-tree adopts sequential write access mode.At the same time,it uses memory buffer to batch new write threads,so it has greater write advantages.Nevertheless,repeated reading and writing of data and unnecessary compression operations lead to the problem of read and write amplification of the LSM-tree.Finally,these problems seriously affect the performance of the system,especially in the data-intensive application scenarios.Nowadays,researches have make great efforts to solve the problems.Firstly,this paper investigates various factors that affect the performance of the LSM-tree,collects a lot of literature on improving the performance of LSM tree-based key-value systems,organizes and categorizes them.Then it discusses their advantages and tradeoffs to enable readers to understand LSM tree-based storage technologies and their optimization strategies.Finally,several representative LSM tree-based key-value storage technologies are surveyed and some potential future research directions are discussed.