Package org.apache.hadoop.mapreduce.lib.aggregate

Interface ValueAggregatorDescriptor

All Known Subinterfaces:
ValueAggregatorDescriptor
All Known Implementing Classes:
UserDefinedValueAggregatorDescriptor, UserDefinedValueAggregatorDescriptor, ValueAggregatorBaseDescriptor, ValueAggregatorBaseDescriptor
@Public @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 Details

  • Method Details

    • 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.