org.apache.hadoop.mapred.lib.aggregate

Interface ValueAggregatorDescriptor

All Known Implementing Classes:

AggregateWordCount.WordCountPlugInClass, AggregateWordHistogram.AggregateWordHistogramPlugin, UserDefinedValueAggregatorDescriptor, ValueAggregatorBaseDescriptor

public interface ValueAggregatorDescriptor

This interface defines the contract a value aggregator descriptor must support. Such a descriptor can be configured with a JobConf object. Its main function is to generate a list of aggregation-id/value pairs. An aggregation id encodes an aggregation type which is used to guide the way to aggregate the value in the reduce/combiner phrase of an Aggregate based job.The mapper in an Aggregate based map/reduce job may create one or more of ValueAggregatorDescriptor objects at configuration time. For each input key/value pair, the mapper will use those objects to create aggregation id/value pairs.

Field Summary

Fields

Modifier and Type	Field and Description
static org.apache.hadoop.io.Text	ONE
static String	TYPE_SEPARATOR

Method Summary

Methods

Modifier and Type	Method and Description
void	configure(JobConf job) Configure the object
ArrayList<Map.Entry<org.apache.hadoop.io.Text,org.apache.hadoop.io.Text>>	generateKeyValPairs(Object key, Object val) Generate a list of aggregation-id/value pairs for the given key/value pair.

Field Detail

TYPE_SEPARATOR

static final String TYPE_SEPARATOR

See Also:

Constant Field Values

ONE

static final org.apache.hadoop.io.Text ONE

Method Detail

generateKeyValPairs

ArrayList<Map.Entry<org.apache.hadoop.io.Text,org.apache.hadoop.io.Text>> generateKeyValPairs(Object key,
                                                                                            Object val)

Generate a list of aggregation-id/value pairs for the given key/value pair. This function is usually called by the mapper of an Aggregate based job.

Parameters:

key - input key

val - input value

Returns:

a list of aggregation id/value pairs. An aggregation id encodes an aggregation type which is used to guide the way to aggregate the value in the reduce/combiner phrase of an Aggregate based job.

configure

void configure(JobConf job)

Configure the object

Parameters:

job - a JobConf object that may contain the information that can be used to configure the object.