Write Behind Logging(WBL) : 영구 메모리를 활용한 LSM 트리 기반의 키-밸류 저장 최적화

학위논문(석사) -- 서울대학교대학원 : 공과대학 컴퓨터공학부, 2022. 8. 염헌영.Current LSM-tree based key-value database systems are optimized for the DRAM-SSD memory architecture. With the emergence of persistent mem- ory(PMEM), which is a non-volatile storage device with performance close to DRAM, memory architecture have changed. In this new hybrid memory ar- chitecture, we need to optimize database system to exploit the benefits given by persistent memory. LSM-tree based key-value database systems suffer from (1)Write Ahead Logging and (2)Write stalls from compaction jobs. In this pa- per, we separate read/write path of the system. First, we write data on per- sistent memory directly, eliminating the need of write ahead logging. Since PMEM provides larger space than DRAM, concerns for compaction stalls di- minish as well. Data written on persistent memory is then forwarded to DRAM. Since DRAM is free of compaction jobs and write path, there are some flexibil- ity of customization to improve read performance. Our work was made above vanilla RocksDB. We evaluate our work by using YCSB workloads, comparing with original version of RocksDB system. The result showed that our system works well on write-intensive workloads, and showed little improvement on read- intensive workloads. Keywords: Persistent Memory, LSM-Tree, Key-Value Database, Write Stalls, Reducing Log Overhead, Separate Read/Write Path현재 LSM 트리 기반의 키-밸류 데이터베이스 시스템은 DRAM-SSD 메모리 구조를 기반으로 최적화되어 있다. 하지만 영구 메모리가 등장함으로서, 메모리 계층구조에 변화가 생겼다. 영구 메모리는 DRAM에 근접한 수준의 성능을 가진 비휘발성메모리이다. 우리는 제 이 하이브리드 메모리 계층구조에서 영구 메모리를 잘 활용해서 데이타베이스 시스템을 새롭게 최적화할 필요가 있다. 보통 LSM 트리 기반의키-밸류 데이터베이스 시스템은 Write-Ahead-Logging(WAL)과 (2)Compaction으로 인한 Write Stall에 의해 성능이 저하되는 문제점을 가지고 있다. 이 연구에서는 영구메모리가 도입된 메모리 계층구조에서 읽기/쓰기 경로를 분리함으로서 이문제를 해결하고자 한다. 먼저 쓰기 경로는 DRAM을 거치지 않고 바로 PMEM에씀으로서 WAL의 필요성을 제거한다. 영구 메모리에 적은 데이터는 후에 DRAM으로 이동한다. DRAM은 compaction이나 쓰기 경로 위에 존재하지 않기 때문에오직 읽기만을 위해 최적화 되기 편해진다. 이 연구는 rocksDB 버전 위에서 코드수정을 통해 진행되었다. 그리고 기존의 rocksDB와의 성능 평가를 위해 YCSB워크로드를 사용했다. 실험 결과를 통해 우리의 연구가 write가 많은 워크로드에서는 주목할만한 성능 개선이 있었고, read가 많은 워크로드에서는 약간의 성능개선이 있다는 것을 알게 되었다.Chapter 1 Introduction 1 1.1 Motivation 2 1.2 Contribution 4 1.3 Outline 5 Chapter 2 Background 6 2.1 Intel Optane Persistent Memory 7 2.2 LSM Tree based Key-Value Database 8 2.3 Related Works 10 Chapter 3 Implementation and Design 13 3.1 Write Path 15 3.2 Read Path 16 Chapter 4 Evaluation 18 4.1 Experimental Setup 18 4.2 Experiment Result 20 Chapter 5 Conclusion 23석

Persistent Buffer Management with Optimistic Consistency

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