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public interface Partitioner<K2,V2>
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| Method Summary | |
|---|---|
int |
getPartition(K2 key,
V2 value,
int numPartitions)
Get the paritition number for a given key (hence record) given the total number of partitions i.e. |
| Methods inherited from interface org.apache.hadoop.mapred.JobConfigurable |
|---|
configure |
| Method Detail |
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int getPartition(K2 key,
V2 value,
int numPartitions)
Typically a hash function on a all or a subset of the key.
key - the key to be paritioned.value - the entry value.numPartitions - the total number of partitions.
key.
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