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Hadoop MapReduce v2 Cookbook - Second Edition by Thilina Gunarathne

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Speculative execution of straggling tasks

One of the main advantages of using Hadoop MapReduce is the framework-managed fault tolerance. When performing a large-scale distributed computation, parts of the computation can fail due to external causes such as network failures, disk failures, and node failures. When Hadoop detects an unresponsive task or a failed task, Hadoop will re-execute those tasks in a new node.

A Hadoop cluster may consist of heterogeneous nodes, and as a result there can be very slow nodes as well as fast nodes. Potentially, a few slow nodes and the tasks executing on those nodes can dominate the execution time of a computation. Hadoop introduces speculative execution optimization to avoid these slow-running tasks, which are ...

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