org.apache.hadoop.mapreduce.lib.partition

Class BinaryPartitioner<V>

java.lang.Object

org.apache.hadoop.mapreduce.Partitioner<BinaryComparable,V>

org.apache.hadoop.mapreduce.lib.partition.BinaryPartitioner<V>

All Implemented Interfaces:

Configurable

Direct Known Subclasses:

BinaryPartitioner

@InterfaceAudience.Public
@InterfaceStability.Evolving
public class BinaryPartitioner<V>
extends Partitioner<BinaryComparable,V>
implements Configurable

Partition BinaryComparable keys using a configurable part of the bytes array returned by BinaryComparable.getBytes().

The subarray to be used for the partitioning can be defined by means of the following properties:

• mapreduce.partition.binarypartitioner.left.offset: left offset in array (0 by default)
• mapreduce.partition.binarypartitioner.right.offset: right offset in array (-1 by default)

Like in Python, both negative and positive offsets are allowed, but the meaning is slightly different. In case of an array of length 5, for instance, the possible offsets are:

  +---+---+---+---+---+
  | B | B | B | B | B |
  +---+---+---+---+---+
    0   1   2   3   4
   -5  -4  -3  -2  -1
 

The first row of numbers gives the position of the offsets 0...5 in the array; the second row gives the corresponding negative offsets. Contrary to Python, the specified subarray has byte i and j as first and last element, repectively, when i and j are the left and right offset.

For Hadoop programs written in Java, it is advisable to use one of the following static convenience methods for setting the offsets:

• setOffsets(org.apache.hadoop.conf.Configuration, int, int)
• setLeftOffset(org.apache.hadoop.conf.Configuration, int)
• setRightOffset(org.apache.hadoop.conf.Configuration, int)

Field Summary

Fields

Modifier and Type	Field and Description
static String	LEFT_OFFSET_PROPERTY_NAME
static String	RIGHT_OFFSET_PROPERTY_NAME

Constructor Summary

Constructors

Constructor and Description
BinaryPartitioner()

Method Summary

Methods

Modifier and Type	Method and Description
Configuration	getConf() Return the configuration used by this object.
int	getPartition(BinaryComparable key, V value, int numPartitions) Use (the specified slice of the array returned by) BinaryComparable.getBytes() to partition.
void	setConf(Configuration conf) Set the configuration to be used by this object.
static void	setLeftOffset(Configuration conf, int offset) Set the subarray to be used for partitioning to bytes[offset:] in Python syntax.
static void	setOffsets(Configuration conf, int left, int right) Set the subarray to be used for partitioning to bytes[left:(right+1)] in Python syntax.
static void	setRightOffset(Configuration conf, int offset) Set the subarray to be used for partitioning to bytes[:(offset+1)] in Python syntax.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

LEFT_OFFSET_PROPERTY_NAME

public static final String LEFT_OFFSET_PROPERTY_NAME

See Also:

Constant Field Values

RIGHT_OFFSET_PROPERTY_NAME

public static final String RIGHT_OFFSET_PROPERTY_NAME

See Also:

Constant Field Values

Constructor Detail

BinaryPartitioner

public BinaryPartitioner()

Method Detail

setOffsets

public static void setOffsets(Configuration conf,
              int left,
              int right)

Set the subarray to be used for partitioning to bytes[left:(right+1)] in Python syntax.

Parameters:

conf - configuration object

left - left Python-style offset

right - right Python-style offset

setLeftOffset

public static void setLeftOffset(Configuration conf,
                 int offset)

Set the subarray to be used for partitioning to bytes[offset:] in Python syntax.

Parameters:

conf - configuration object

offset - left Python-style offset

setRightOffset

public static void setRightOffset(Configuration conf,
                  int offset)

Set the subarray to be used for partitioning to bytes[:(offset+1)] in Python syntax.

Parameters:

conf - configuration object

offset - right Python-style offset

setConf

public void setConf(Configuration conf)

Description copied from interface: Configurable

Set the configuration to be used by this object.

Specified by:

setConf in interface Configurable

getConf

public Configuration getConf()

Description copied from interface: Configurable

Return the configuration used by this object.

Specified by:

getConf in interface Configurable

getPartition

public int getPartition(BinaryComparable key,
               V value,
               int numPartitions)

Use (the specified slice of the array returned by) BinaryComparable.getBytes() to partition.

Specified by:

getPartition in class Partitioner<BinaryComparable,V>

Parameters:

key - the key to be partioned.

value - the entry value.

numPartitions - the total number of partitions.

Returns:

the partition number for the key.