setOutputValueGroupingComparator与setOutputKeyComparatorClass
2011-09-04 11:01
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如果需要中间过程对key的分组规则和reduce前对key的分组规则不同,那么可以通过 JobConf.setOutputValueGroupingComparator(Class)来指定一个Comparator。再加上 JobConf.setOutputKeyComparatorClass(Class)可用于控制中间过程的key如何被分组,所以结合两者可以实现按值的二次排序。
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