@InterfaceAudience.Public @InterfaceStability.Stable public abstract class Partitioner<KEY,VALUE> extends Object
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.
Partitioner is created only when there are multiple
Note: If you require your Partitioner class to obtain the Job's
configuration object, implement the
|Constructor and Description|
|Modifier and Type||Method and Description|
Get the partition number for a given key (hence record) given the total number of partitions i.e.
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.
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