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java.lang.Objectorg.apache.hadoop.mapreduce.Partitioner<KEY,VALUE>
public abstract class Partitioner<KEY,VALUE>
Partitions the key space.
Partitioner controls the partitioning of the keys of the
intermediate map-outputs. The key (or a subset of the key) is used to derive
the partition, typically by a hash function. The total number of partitions
is the same as the number of reduce tasks for the job. Hence this controls
which of the m reduce tasks the intermediate key (and hence the
record) is sent for reduction.
Reducer| Constructor Summary | |
|---|---|
Partitioner()
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| Method Summary | |
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abstract int |
getPartition(KEY key,
VALUE value,
int numPartitions)
Get the partition number for a given key (hence record) given the total number of partitions i.e. |
| Methods inherited from class java.lang.Object |
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clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
| Constructor Detail |
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public Partitioner()
| Method Detail |
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public abstract int getPartition(KEY key,
VALUE value,
int numPartitions)
Typically a hash function on a all or a subset of the key.
key - the key to be partioned.value - the entry value.numPartitions - the total number of partitions.
key.
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