Hadoop speculative execution

You can found a good description about speculative execution at Wikipedia. Here are the two properties to configure the use of this feature:

mapred.map.tasks.speculative.execution
mapred.reduce.tasks.speculative.execution

Or if you are using Hadoop 2.x:

mapreduce.map.speculative
mapreduce.reduce.speculative

Most time it is useful but in some scenarios disabling it will make a big difference.

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