org.apache.giraph.reducers

Interface ReduceOperation<S,R extends org.apache.hadoop.io.Writable>

Type Parameters:

S - Single value type, objects passed on workers

R - Reduced value type

All Superinterfaces:

org.apache.hadoop.io.Writable

All Known Implementing Classes:

AggregatorReduceOperation, AndReduce, ArrayReduce, BasicArrayReduce, BasicMapReduce, CollectPrimitiveReduceOperation, CollectReduceOperation, CollectTuplesOfPrimitivesReduceOperation, KryoWrappedReduceOperation, LongXorReduce, MaxPairReducer, MaxReduce, MinReduce, OrReduce, PairReduce, ReducersBenchmark.TestLongSumReducer, ReduceSameTypeOperation, SumReduce, TopNReduce

public interface ReduceOperation<S,R extends org.apache.hadoop.io.Writable>
extends org.apache.hadoop.io.Writable

Reduce operations defining how to reduce single values passed on workers, into partial values on workers, and then into a single global reduced value. Object should be thread safe. Most frequently it should be immutable object, so that functions can execute concurrently. Rarely when object is mutable (AggregatorReduceOperation), i.e. stores reusable object inside, accesses should be synchronized.

Method Summary

Modifier and Type	Method and Description
R	createInitialValue() Return new reduced value which is neutral to reduce operation.
R	reduce(R curValue, S valueToReduce) Add a new value.
R	reduceMerge(R curValue, R valueToReduce) Add partially reduced value to current partially reduced value.

Methods inherited from interface org.apache.hadoop.io.Writable

readFields, write

Method Detail

createInitialValue

R createInitialValue()

Return new reduced value which is neutral to reduce operation.

Returns:

Neutral value

reduce

R reduce(R curValue,
         S valueToReduce)

Add a new value. Needs to be commutative and associative Commonly, returned value should be same as curValue argument.

Parameters:

curValue - Partial value into which to reduce and store the result

valueToReduce - Single value to be reduced

Returns:

reduced value

reduceMerge

R reduceMerge(R curValue,
              R valueToReduce)

Add partially reduced value to current partially reduced value. Commonly, returned value should be same as curValue argument.

Parameters:

curValue - Partial value into which to reduce and store the result

valueToReduce - Partial value to be reduced

Returns:

reduced value