org.apache.beam.sdk.state

Interface CombiningState<InputT,AccumT,OutputT>

Type Parameters:

InputT - the type of values added to the state

AccumT - the type of accumulator

OutputT - the type of value extracted from the state

All Superinterfaces:

GroupingState<InputT,OutputT>, ReadableState<OutputT>, State

@Experimental(value=STATE)
public interface CombiningState<InputT,AccumT,OutputT>
extends GroupingState<InputT,OutputT>

A ReadableState cell defined by a Combine.CombineFn, accepting multiple input values, combining them as specified into accumulators, and producing a single output value.

Implementations of this form of state are expected to implement GroupingState.add(InputT) efficiently, not via a sequence of read-modify-write.

Method Summary

Modifier and Type	Method and Description
void	addAccum(AccumT accum) Add an accumulator to this state cell.
AccumT	getAccum() Read the merged accumulator for this state cell.
AccumT	mergeAccumulators(java.lang.Iterable<AccumT> accumulators) Merge the given accumulators according to the underlying Combine.CombineFn.
CombiningState<InputT,AccumT,OutputT>	readLater() Indicate that the value will be read later.

Methods inherited from interface org.apache.beam.sdk.state.GroupingState

add, isEmpty

Methods inherited from interface org.apache.beam.sdk.state.ReadableState

read

Methods inherited from interface org.apache.beam.sdk.state.State

clear

Method Detail

getAccum

AccumT getAccum()

Read the merged accumulator for this state cell. It is implied that reading the state involves reading the accumulator, so readLater() is sufficient to prefetch for this.

addAccum

void addAccum(AccumT accum)

Add an accumulator to this state cell. Depending on implementation this may immediately merge it with the previous accumulator, or may buffer this accumulator for a future merge.

mergeAccumulators

AccumT mergeAccumulators(java.lang.Iterable<AccumT> accumulators)

Merge the given accumulators according to the underlying Combine.CombineFn.

readLater

CombiningState<InputT,AccumT,OutputT> readLater()

Description copied from interface: ReadableState

Indicate that the value will be read later.

This allows an implementation to start an asynchronous prefetch or to include this state in the next batch of reads.

Specified by:

readLater in interface GroupingState<InputT,OutputT>

Specified by:

readLater in interface ReadableState<OutputT>

Returns:

this for convenient chaining