Parallélisme de donnée

Résumé

Le parallélisme par distribution de donnée ou parallélisme de donnée (data parallelism en anglais) est un paradigme de la programmation parallèle. Autrement dit, c'est une manière particulière d'écrire des programmes pour des machines parallèles. Les algorithmes des programmes qui entrent dans cette catégorie cherchent à distribuer les données au sein des processus et à y opérer les mêmes opérations à l'instar des SIMD. Le paradigme opposé est celui du parallélisme de tâche. Notes et références Catégorie:Programmation concurrente Catégorie:Calcul parallèle

Source officielle

https://fr.wikipedia.org/wiki/Parall%C3%A9lisme_de_donn%C3%A9e

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RCMP: Enabling Efficient Recomputation Based Failure Resilience for Big Data Analytics

Florin Dinu

Data replication, the main failure resilience strategy used for big data analytics jobs, can be unnecessarily inefficient. It can cause serious performance degradation when applied to intermediate job outputs in multi-job computations. For instance, for I/O-intensive big data jobs, data replication is especially expensive because very large datasets need to be replicated. Reducing the number of replicas is not a satisfactory solution as it only aggravates a fundamental limitation of data replication: its failure resilience guarantees are limited by the number of available replicas. When all replicas of some piece of intermediate job output are lost, cascading job recomputations may be required for recovery. In this paper we show how job recomputation can be made a first-order failure resilience strategy for big data analytics. The need for data replication can thus be significantly reduced. We present RCMP, a system that performs efficient job recomputation. RCMP can persist task outputs across jobs and leverage them to minimize the work performed during job recomputations. More importantly, RCMP addresses two important challenges that appear during job recomputations. The first is efficiently utilizing the available compute node parallelism. The second is dealing with hot-spots. RCMP handles both by switching to a finer-grained task scheduling granularity for recomputations. Our experiments show that RCMP's benefits hold across two different clusters, for job inputs as small as 40GB or as large as 1.2TB. Compared to RCMP, data replication is 30%-100% worse during failure-free periods. More importantly, by efficiently performing recomputations, RCMP is comparable or better even under single and double data loss events.

2014

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Understanding the performance of data-parallel workloads when resource-constrained has significant practical importance but unfortunately has received only limited attention. This paper identifies, quantifies and demonstrates memory elasticity, an intrinsic property of data-parallel tasks. Memory elasticity allows tasks to run with significantly less memory that they would ideally want while only paying a moderate performance penalty. For example, we find that given as little as 10% of ideal memory, PageRank and NutchIndexing Hadoop reducers become only 1.2x/1.75x and 1.08x slower. We show that memory elasticity is prevalent in the Hadoop, Spark, Tez and Flink frameworks. We also show that memory elasticity is predictable in nature by building simple models for Hadoop and extending them to Tez and Spark. To demonstrate the potential benefits of leveraging memory elasticity, this paper further explores its application to cluster scheduling. In this setting, we observe that the resource vs. time trade-off enabled by memory elasticity becomes a task queuing time vs task runtime trade-off. Tasks may complete faster when scheduled with less memory because their waiting time is reduced. We show that a scheduler can turn this task-level trade-off into improved job completion time and cluster-wide memory utilization. We have integrated memory elasticity into Apache YARN. We show gains of up to 60% in average job completion time on a 50-node Hadoop cluster. Extensive simulations show similar improvements over a large number of scenarios.

The USENIX Association2017

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Don't cry over spilled records: Memory elasticity of data-parallel applications and its application to cluster scheduling

Florin Dinu, Wajih Ul Hassan, Calin Iorgulescu, Syed Mohammad Aunn Raza, Willy Zwaenepoel

2017

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