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HopsFS: Scaling Hierarchical File System Metadata Using NewSQL Databases
KTH, School of Information and Communication Technology (ICT), Software and Computer systems, SCS.ORCID iD: 0000-0002-1672-6899
KTH, School of Information and Communication Technology (ICT), Software and Computer systems, SCS.ORCID iD: 0000-0002-6578-3902
KTH, School of Information and Communication Technology (ICT), Software and Computer systems, SCS.ORCID iD: 0000-0002-6718-0144
KTH, School of Information and Communication Technology (ICT), Software and Computer systems, SCS.ORCID iD: 0000-0002-9484-6714
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2017 (English)In: 15th USENIX Conference on File and Storage Technologies, FAST 2017, Santa Clara, CA, USA, February 27 - March 2, 2017, USENIX Association , 2017, p. 89-103Conference paper, Published paper (Refereed)
Abstract [en]

Recent improvements in both the performance and scalability of shared-nothing, transactional, in-memory NewSQL databases have reopened the research question of whether distributed metadata for hierarchical file systems can be managed using commodity databases. In this paper, we introduce HopsFS, a next generation distribution of the Hadoop Distributed File System (HDFS) that replaces HDFS’ single node in-memory metadata service, with a distributed metadata service built on a NewSQL database. By removing the metadata bottleneck, HopsFS enables an order of magnitude larger and higher throughput clusters compared to HDFS. Metadata capacity has been increased to at least 37 times HDFS’ capacity, and in experiments based on a workload trace from Spotify, we show that HopsFS supports 16 to 37 times the throughput of Apache HDFS. HopsFS also has lower latency for many concurrent clients, and no downtime during failover. Finally, as metadata is now stored in a commodity database, it can be safely extended and easily exported to external systems for online analysis and free-text search.

Place, publisher, year, edition, pages
USENIX Association , 2017. p. 89-103
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-205355ISI: 000427295900007OAI: oai:DiVA.org:kth-205355DiVA, id: diva2:1088701
Conference
15th USENIX Conference on File and Storage Technologies, FAST 2017, Santa Clara, CA, USA, February 27 - March 2, 2017
Funder
EU, FP7, Seventh Framework Programme, 317871Swedish Foundation for Strategic Research , E2E-Clouds
Note

QC 20170424

Available from: 2017-04-13 Created: 2017-04-13 Last updated: 2018-11-05Bibliographically approved
In thesis
1. Scaling Distributed Hierarchical File Systems Using NewSQL Databases
Open this publication in new window or tab >>Scaling Distributed Hierarchical File Systems Using NewSQL Databases
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

For many years, researchers have investigated the use of database technology to manage file system metadata, with the goal of providing extensible typed metadata and support for fast, rich metadata search. However, earlier attempts failed mainly due to the reduced performance introduced by adding database operations to the file system’s critical path. Recent improvements in the performance of distributed in-memory online transaction processing databases (NewSQL databases) led us to re-investigate the possibility of using a database to manage file system metadata, but this time for a distributed, hierarchical file system, the Hadoop Distributed File System (HDFS). The single-host metadata service of HDFS is a well-known bottleneck for both the size of the HDFS clusters and their throughput.In this thesis, we detail the algorithms, techniques, and optimizations used to develop HopsFS, an open-source, next-generation distribution of the HDFS that replaces the main scalability bottleneck in HDFS, single node in-memory metadata service, with a no-shared state distributed system built on a NewSQL database. In particular, we discuss how we exploit recent high-performance features from NewSQL databases, such as application-defined partitioning, partition pruned index scans, and distribution aware transactions, as well as more traditional techniques such as batching and write-ahead caches, to enable a revolution in distributed hierarchical file system performance.HDFS’ design is optimized for the storage of large files, that is, files ranging from megabytes to terabytes in size. However, in many production deployments of the HDFS, it has been observed that almost 20% of the files in the system are less than 4 KB in size and as much as 42% of all the file system operations are performed on files less than 16 KB in size. HopsFS introduces a tiered storage solution to store files of different sizes more efficiently. The tiers range from the highest tier where an in-memory NewSQL database stores very small files (<1 KB), to the next tier where small files (<64 KB) are stored in solid-state-drives (SSDs), also using a NewSQL database, to the largest tier, the existing Hadoop block storage layer for very large files. Our approach is based on extending HopsFS with an inode stuffing technique, where we embed the contents of small files with the metadata and use database transactions and database replication guarantees to ensure the availability, integrity, and consistency of the small files. HopsFS enables significantly larger cluster sizes, more than an order of magnitude higher throughput, and significantly lower client latencies for large clusters.Lastly, coordination is an integral part of the distributed file system operations protocols. We present a novel leader election protocol for partially synchronous systems that uses NewSQL databases as shared memory. Our work enables HopsFS, that uses a NewSQL database to save the operational overhead of managing an additional third-party service for leader election and deliver performance comparable to a leader election implementation using a state-of-the-art distributed coordination service, ZooKeeper.

Abstract [sv]

I många år har forskare undersökt användningen av databasteknik för att hantera metadata i filsystem, med målet att tillhandahålla förlängbar metadata med stöd för snabb och uttrycksfull metadatasökning. Tidigare försök misslyckades dock huvudsakligen till följd av den reducerade prestanda som infördes genom att lägga till databasoperationer på filsystemets kritiska väg. De senaste prestandaförbättringarna för OLTP databaser som lagras i minnet (NewSQL databaser) ledde oss till att undersöka möjligheten att använda en databas för att hantera filsystemmetadata, men den här gången för ett distribuerat hierarkiskt filsystem, Hadoop Distributed Filesystem (HDFS). Metadata i HDFS lagras på en maskin, vilket är en känd flaskhals för såväl storlek som prestandan för HDFS kluster.I denna avhandling redogör vi för de algoritmer, tekniker och optimeringar som används för att utveckla HopsFS, en med öppen källkod, nästa generationens distribution av HDFS som ersätter lagringen av metadata i HDFS, där den lagras enbart i minnet på en nod, med ett distribuerat system med delat tillstånd byggt på en NewSQL databas. I synnerhet diskuteras hur vi utnyttjar nyligen framtagen högpresterande funktionalitet från NewSQL-databaser, exempelvis applikationsdefinierad partitionering, partitionsskuren indexskanning och distributionsmedvetna transaktioner, samt mer traditionella tekniker som batching och skrivcache, som banar väg för en revolution inom prestanda för distribuerade filsystem.HDFS design är optimerad för lagring av stora filer, det vill säga filer som sträcker sig från megabyte till terabyte i storlek. Men i många installationer i produktionsystem har det observerats att nästan 20 procent av filerna i systemet är mindre än 4 KB i storlek och så mycket som 42 procent av alla filsystemsoperationer utförs på filer mindre än 16 KB i storlek. HopsFS introducerar en nivåbaserad uppdelning av olika filstorlekar för mer effektiv lagring . Nivåerna varierar från högsta nivån där en NewSQL-databas lagrar i minnet mycket små filer (<1 KB), till nästa nivå där små filer (<64 KB) lagras i SSD-enheter (Solid State Drives) en NewSQL-databas, till den största delen, det befintliga Hadoop-blocklagringsskiktet för mycket stora filer. Vårt tillvägagångssätt bygger på att utöka HopsFS med en utfyllningsteknik för filer, där vi lägger in innehållet i små filer tillsammans med metadata och använder databasstransaktioner och databasreplikation för att garantera de små filernas tillgänglighet, integritet och konsistens säkerställs. HopsFS möjliggör signifikant större klusterstorlekar, mer än en storleksordning högre transaktionsgenomströmning, och signifikant lägre latens för klienter till stora kluster.Slutligen är koordinering en central del av protokollet för distribuerade filsystemsoperationer. Vi presenterar ett nytt ledarval protokoll för delvis synkrona system som använder NewSQL databaser som delat minne. Vårt arbete möjliggör HopsFS, som använder en NewSQL-databas för att spara in på de operativa kostnader det skulle medföra att hantera en ytterligare tredjepartstjänst för ledarval. Protokollets prestanda kan jämföras med en ledarval implementation I ZooKeeper, som är en modern distribuerad koordinationsservice.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2018. p. 196
Series
TRITA-EECS-AVL ; 2018 : 79
National Category
Computer Systems
Research subject
Information and Communication Technology
Identifiers
urn:nbn:se:kth:diva-238605 (URN)978-91-7729-987-5 (ISBN)
Public defence
2018-12-07, Sal-B, Electrum, Kungliga Tekniska Högskolan, Kistagången 16, Kista, Stockholm, 13:45 (English)
Opponent
Supervisors
Available from: 2018-11-05 Created: 2018-11-05 Last updated: 2018-11-06Bibliographically approved

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Published versionhttps://www.usenix.org/conference/fast17

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Niazi, SalmanIsmail, MahmoudHaridi, SeifDowling, Jim

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