On Understanding the Energy Impact of Speculative Execution in Hadoop Hadoop emerged as an important system for large scale data analysis. Speculative execution is a key feature in Hadoop that is extensively leveraged in clouds: it is used to mask slow tasks (i.e., stragglers) xe2x80x94 resulted from resource contention and heterogeneity in clouds xe2x80x94 by launching speculative task copies on other machines. However, speculative execution is not costfree and may result in performance degradation and extra resource and energy consumption. While prior literature has been dedicated to improving stragglers detection to cope with the inevitable heterogeneity in clouds, little work is focusing on understanding the implications of speculative execution on the performance and energy consumption in Hadoop cluster. In this paper, we have designed a set of experiments to evaluate the impact of speculative execution on the performance and energy consumption of Hadoop in homo and heterogeneous environments. Our studies reveal that speculative execution may sometimes reduce, sometimes increase the energy consumption of Hadoop clusters. This strongly depends on the reduction in the execution time of MapReduce applications and on the extra power consumption introduced by speculative execution. Moreover, we show that the extra power consumption varies inbetween applications and is contributed to by three main factors: the duration of speculative tasks, the idle time, and the allocation of speculative tasks. To the best of our knowledge, our work provides the first deep look into the energy efficiency of speculative execution in Hadoop.

Effective Straggler Mitigation with CrossLayer InterferenceAware Optimization Inmemory data processing frameworks (e.g., Spark) make big data analysis greatly simpler and efficient. However, stragglers that take much longer to finish than other tasks significantly degrade performance. There exist multiple factors that cause stragglers, either from the hardware resource layer or application layer, e.g. hardware heterogeneity, interference, data locality and data skew. While stateoftheart straggler mitigation techniques have presented partial solutions on data skew and data locality, we find that the other factors can also result in serious problems. We present Clio, a crosslayer interferenceaware optimization system that can effectively mitigate stragglers for data processing frameworks. Clio supports the scheduling of both map and reduce tasks. It heuristically dispatches intermediate data in proportion to the actual computing ability of each worker node, which is estimated considering various straggler factors, to balance the completion times of tasks in a much finer way. We implement Clio in Apache Spark, and evaluate its performance using both synthetic and real datasets. Experiment results show that, Clio can speed up the execution of applications by up to 67%, compared with the existing algorithms.