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小议“限时作业”
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作者 龙作栋 《小学教学参考(数学版)》 2004年第11期48-48,共1页
在乡下听课中,笔者发现有些教师课堂教学时间安排不当,大多把课堂作业放在课外让学生去完成。这样完成作业弊端不少,一是加重学生课外负担;二是造成学生拖拉作风,不利养成按时完成作业的习惯;三是会造成有的学生抄袭作业,不能真... 在乡下听课中,笔者发现有些教师课堂教学时间安排不当,大多把课堂作业放在课外让学生去完成。这样完成作业弊端不少,一是加重学生课外负担;二是造成学生拖拉作风,不利养成按时完成作业的习惯;三是会造成有的学生抄袭作业,不能真实地反映教学中的问题。 展开更多
关键词 “限时作业” 小学 数学教学 教学效率 作业设计
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Meeting deadlines for approximation processing in MapReduce environments
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作者 Ming-hao HU Chang-jian WANG Yu-xing PENG 《Frontiers of Information Technology & Electronic Engineering》 SCIE EI CSCD 2017年第11期1754-1772,共19页
To provide timely results for big data analytics, it is crucial to satisfy deadline requirements for MapReduce jobs in today's production environments. Much effort has been devoted to the problem of meeting deadlines... To provide timely results for big data analytics, it is crucial to satisfy deadline requirements for MapReduce jobs in today's production environments. Much effort has been devoted to the problem of meeting deadlines, and typically there exist two kinds of solutions. The first is to allocate appropriate resources to complete the entire job before the specified time limit, where missed deadlines result because of tight deadline constraints or lack of resources; the second is to run a pre-constructed sample based on deadline constraints, which can satisfy the time requirement but fail to maximize the volumes of processed data. In this paper, we propose a deadline-oriented task scheduling approach, named 'Dart', to address the above problem. Given a specified deadline and restricted resources, Dart uses an iterative estimation method, which is based on both historical data and job running status to precisely estimate the real-time job completion time. Based on the estimated time, Dart uses an approach-revise algorithm to make dynamic scheduling decisions for meeting deadlines while maximizing the amount of processed data and mitigating stragglers. Dart also efficiently handles task failures and data skew, protecting its performance from being harmed. We have validated our approach using workloads from OpenCloud and Facebook on a cluster of 64 virtual machines. The results show that Dart can not only effectively meet the deadline but also process near-maximum volumes of data even with tight deadlines and limited resources. 展开更多
关键词 MAPREDUCE Approximation jobs DEADLINE Task scheduling Straggler mitigation
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