job.setOutputValueComparatorClass(theClass) should be supported
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Key: HADOOP-686
URL: http://issues.apache.org/jira/browse/HADOOP-686
Project: Hadoop
Issue Type: New Feature
Components: mapred
Environment: all environment
Reporter: Feng Jiang
if the input of Reduce phase is :
K2, V3
K2, V2
K1, V5
K1, V3
K1, V4
in the current hadoop, the reduce output could be:
K1, (V5, V3, V4)
K2, (V3, V2)
But I hope hadoop supports job.setOutputValueComparatorClass(theClass), so that
i can make values are in order, and the output could be:
K1, (V3, V4, V5)
K2, (V2, V3)
This feature is very important, I think. Without it, we have to take the
sorting by ourselves, and have to worry about the possibility that the values
are too large to fit into memory. Then the codes becomes too hard to read. That
is the reason why i think this feature is so important, and should be done in
the hadoop framework.
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