org.apache.hadoop.mapreduce.lib.aggregate
Interface ValueAggregatorDescriptor

All Known Subinterfaces:

ValueAggregatorDescriptor

All Known Implementing Classes:

UserDefinedValueAggregatorDescriptor, UserDefinedValueAggregatorDescriptor, ValueAggregatorBaseDescriptor, ValueAggregatorBaseDescriptor

@InterfaceAudience.Public
@InterfaceStability.Stable
public interface ValueAggregatorDescriptor

This interface defines the contract a value aggregator descriptor must support. Such a descriptor can be configured with a Configuration 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(Configuration conf) 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(Configuration conf)

Configure the object

Parameters:

conf - a Configuration object that may contain the information that can be used to configure the object.