LSM-tree based Database System Optimization using Application-Driven Flash Management

학위논문(석사)--서울대학교 대학원 :공과대학 컴퓨터공학부,2019. 8. 염헌영.Modern data centers aim to take advantage of high parallelism in storage de- vices for I/O intensive applications such as storage servers, cache systems, and key-value stores. Key-value stores are the most typical applications that should provide a highly reliable service with high-performance. To increase the I/O performance of key-value stores, many data centers have actively adopted next- generation storage devices such as Non-Volatile Memory Express (NVMe) based Solid State Devices (SSDs). NVMe SSDs and its protocol are characterized to provide a high degree of parallelism. However, they may not guarantee pre- dictable performance while providing high performance and parallelism. For example, heavily mixed read and write requests can result in performance degra- dation of throughput and response time due to the interference between the requests and internal operations (e.g., Garbage Collection (GC)). To minimize the interference and provide higher performance, this paper presents IsoKV, an isolation scheme for key-value stores by exploiting internal parallelism in SSDs. IsoKV manages the level of parallelism of SSD directly by running application-driven flash management scheme. By storing data with dif- ferent characteristics in each dedicated internal parallel units of SSD, IsoKV re- duces interference between I/O requests. We implement IsoKV on RocksDB and evaluate it using Open-Channel SSD. Our extensive experiments have shown that IsoKV improves overall throughput and response time on average 1.20× and 43% compared with the existing scheme, respectively.최신 데이터 센터는 스토리지 서버, 캐시 시스템 및 Key-Value stores와 같은 I/O 집약적인 애플리케이션을 위한 스토리지 장치의 높은 병렬성을 활용하는 것을 목표로 한다. Key-value stores는 고성능의 고신뢰 서비스를 제공해야 하는 가장 대표적인 응용프로그램이다. Key-value stores의 I/O 성능을 높이기 위해 많은 데 이터 센터가 비휘발성 메모리 익스프레스(NVMe) 기반 SSD(Solid State Devices) 와 같은 차세대 스토리지 장치를 적극적으로 채택하고 있다. NVMe SSD와 그 프 로토콜은 높은 수준의 병렬성을 제공하는 것이 특징이다. 그러나 NVMe SSD가 병렬성을 제공하면서도 예측 가능한 성능을 보장하지는 못할 수 있다. 예를 들어 읽기 및 쓰기 요청이 많이 혼합되면 요청과 내부 작업(예: GC) 사이의 간섭으로 인해 처리량 및 응답 시간의 성능 저하가 발생할 수 있다. 간섭을 최소화하고 성능을 향상시키기 위해 본 연구에서는 Key-value stores를 위한 격리 방식인 IsoKV를 제시한다. IsoKV는 애플리케이션 중심 플래시 저장장 치 관리 방식을 통해 SSD의 병렬화 수준을 직접 관리한다. IsoKV는 SSD의 각 전용 내부 병렬 장치에 서로 다른 특성을 가진 데이터를 저장함으로써 I/O 요청 간의 간섭을 줄인다. 또한 IsoKV는 SSD의 LSM 트리 로직과 데이터 관리를 동기화하 여 GC를 제거한다. 본 연구에서는 RocksDB를 기반으로 IsoKV를 구현하였으며, Open-Channel SSD를 사용하여 성능평가하였다.. 본 연구의 실험 결과에 따르면 IsoKV는 기존의 데이터 저장 방식과 비교하여 평균 1.20× 빠르고 및 43% 감소된 처리량과 응답시간 성능 개선 결과를 얻었다. 관점에서 43% 감소하였다.Abstract Introduction 1 Background 8 Log-Structured Merge tree based Database 8 Open-Channel SSDs 9 Preliminary Experimental Evaluation using oc bench 10 Design and Implementation 14 Overview of IsoKV 14 GC-free flash storage management synchronized with LSM-tree logic 15 I/O type Isolation through Application-Driven Flash Management 17 Dynamic Arrangement of NAND-Flash Parallelism 19 Implementation 21 Evaluation 23 Experimental Setup 23 Performance Evaluation 25 Related Work 31 Conclusion 34 Bibliography 35 초록 40Maste

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