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.


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