Spark Gitbooks: Avoid GroupByKey the reduceByKey example works much better on a large dataset. That's...

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Spark Gitbooks: Avoid GroupByKey

the reduceByKey example works much better on a large dataset. That's because Spark knows it can combine output with a common key on each partition before shuffling the data.

combineByKey can be used when you are combining elements but your return type differs from your input value type.

foldByKey merges the values for each key using an associative function and a neutral "zero value".

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Job aborted due to stage failure: Task not serializable:

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