org.apache.flink.api.common.accumulators

Interface Accumulator<V,R extends Serializable>

Type Parameters:

V - Type of values that are added to the accumulator

R - Type of the accumulator result as it will be reported to the client

All Superinterfaces:

Cloneable, Serializable

All Known Subinterfaces:

SimpleAccumulator<T>

All Known Implementing Classes:

AverageAccumulator, DoubleCounter, DoubleMaximum, DoubleMinimum, EmptyFieldsCountAccumulator.VectorAccumulator, Histogram, IntCounter, IntMaximum, IntMinimum, ListAccumulator, LongCounter, LongMaximum, LongMinimum, SerializedListAccumulator, Utils.ChecksumHashCode

@Public
public interface Accumulator<V,R extends Serializable>
extends Serializable, Cloneable

Accumulators collect distributed statistics or aggregates in a from user functions and operators. Each parallel instance creates and updates its own accumulator object, and the different parallel instances of the accumulator are later merged. merged by the system at the end of the job. The result can be obtained from the result of a job execution, or from the web runtime monitor.

The accumulators are inspired by the Hadoop/MapReduce counters.

The type added to the accumulator might differ from the type returned. This is the case e.g. for a set-accumulator: We add single objects, but the result is a set of objects.

Method Summary

Modifier and Type	Method and Description
void	add(V value)
Accumulator<V,R>	clone() Duplicates the accumulator.
R	getLocalValue()
void	merge(Accumulator<V,R> other) Used by system internally to merge the collected parts of an accumulator at the end of the job.
void	resetLocal() Reset the local value.

Method Detail

add

void add(V value)

Parameters:

value - The value to add to the accumulator object

getLocalValue

R getLocalValue()

Returns:

local The local value from the current UDF context

resetLocal

void resetLocal()

Reset the local value. This only affects the current UDF context.

merge

void merge(Accumulator<V,R> other)

Used by system internally to merge the collected parts of an accumulator at the end of the job.

Parameters:

other - Reference to accumulator to merge in.

clone

Accumulator<V,R> clone()

Duplicates the accumulator. All subclasses need to properly implement cloning and cannot throw a CloneNotSupportedException

Returns:

The duplicated accumulator.