Abstract
Based on a log-structured merge (LSM) tree, the key-value (KV) storage system can provide high reading performance and optimize random writing performance. It is widely used in modern data storage systems like e-commerce, online analytics, and real-time communication. An LSM tree stores new KV data in the memory and flushes to disk in batches. To prevent data loss in memory if there is an unexpected crash, RocksDB appends updating data in the write-ahead log (WAL) before updating the memory. However, synchronous WAL significantly reduces writing performance. In this paper, we present a new WAL mechanism named MyWAL. It directly manages raw devices (or partitions) instead of saving data on a traditional file system. These can avoid useless metadata updating and write data sequentially on disks. Experimental results show that MyWAL can significantly improve the data writing performance of RocksDB compared to the traditional WAL for small KV data on solid-state disks (SSDs), as much as five to eight times faster. On non-volatile memory express soild-state drives (NVMe SSDs) and non-volatile memory (NVM), MyWAL can improve data writing performance by 10%–30%. Furthermore, the results of YCSB (Yahoo! Cloud Serving Benchmark) show that the latency decreased by 50% compared with SpanDB.
摘要
基于日志结构合并(LSM)树的键值(KV)存储系统可优化随机写入性能, 并提高读取性能, 因此被广泛应用于电子商务、 在线分析和实时通信等现代数据存储系统. 日志结构合并树将变更的KV数据存在内存中, 批量刷新至内存, 优化了随机写入效率, 但是在系统意外崩溃时会有数据丢失. 为了避免内存中的数据丢失, RocksDB在更新内存之前, 会将数据写入写前日志(WAL)中. 但是开启同步WAL后系统的写入性能会受到较大的影响. 在本文中, 我们分析了利用本地文件系统保存WAL的一些缺陷, 在此基础上提出了一种新的WAL机制, 该机制根据WAL文件的特性直接管理原始设备(或分区), 避免了无用的元数据更新, 同时保证了数据顺序写入磁盘. 实验结果表明, 对于固态硬盘(SSD)SSD上的小KV数据, MyWAL可以将RocksDB的数据写入性能提高5到8倍. 在NVMe SSD和非易失性存储器(NVM)上, MyWAL可以将数据写入性能提高10%–30%. 此外, YCSB的结果表明, 与SpanDB相比, 写入延迟降低了50%.
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The data that support the findings of this study are available from the corresponding author upon reasonable request.
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Xiao ZHANG and Mengyu LI designed the research. Mengyu LI and Yonghao CHEN processed the data. Mengyu LI drafted the paper. Xiao ZHANG helped organize the paper. Xiao ZHANG, Mengyu LI, Michael NGULUBE, Yonghao CHEN, and Yiping ZHAO revised and finalized the paper.
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Xiao ZHANG, Mengyu LI, Michael NGULUBE, Yonghao CHEN, and Yiping ZHAO declare that they have no conflict of interest.
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Project supported by the National Key Research and Development Project of China (No. 2022YFB2702101), the Shaanxi Province Key Industrial Projects, China (Nos. 2021ZDLGY03-02 and 2021ZDLGY03-08), and the National Natural Science Foundation of China (No. 92152301)
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Zhang, X., Li, M., Ngulube, M. et al. MyWAL: performance optimization by removing redundant input/output stack in key-value store. Front Inform Technol Electron Eng 24, 980–993 (2023). https://doi.org/10.1631/FITEE.2200496
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DOI: https://doi.org/10.1631/FITEE.2200496
Key words
- Key-value (KV) store
- Log-structured merge (LSM) tree
- Non-volatile memory (NVM)
- Non-volatile memory express soild-state drive (NVMe SSD)
- Write-ahead log (WAL)