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
static Text ONE
           
static String TYPE_SEPARATOR
           
 
Method Summary
 void configure(JobConf job)
          Configure the object
 ArrayList<Map.Entry<Text,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 Text ONE
Method Detail

generateKeyValPairs

ArrayList<Map.Entry<Text,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.


Copyright © 2009 The Apache Software Foundation