com.hazelcast.jet.core

Interface WatermarkEmissionPolicy

All Superinterfaces:

Serializable

Functional Interface:

This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.

@FunctionalInterface
public interface WatermarkEmissionPolicy
extends Serializable

A policy object that decides when the watermark has advanced enough to require emitting a new watermark item. For example, a sliding/tumbling window processor doesn't need to observe more than one watermark item per frame.

Method Summary

Modifier and Type	Method and Description
static WatermarkEmissionPolicy	emitByFrame(SlidingWindowPolicy wDef) Returns a watermark emission policy that ensures that the value of the emitted watermark belongs to a frame higher than the previous watermark's frame, as per the supplied WindowDefinition.
static WatermarkEmissionPolicy	emitByMinStep(long minStep) Returns a watermark emission policy that ensures that each emitted watermark's value is at least minStep more than the previous one.
static WatermarkEmissionPolicy	noThrottling() Returns a policy that does no throttling: emits each watermark.
long	throttleWm(long currentWm, long lastEmittedWm) Decides which watermark to emit based on the supplied currentWm value and lastEmittedWm.

Method Detail

throttleWm

long throttleWm(long currentWm,
                long lastEmittedWm)

Decides which watermark to emit based on the supplied currentWm value and lastEmittedWm. We expect the currentWm > lastEmittedWm.

noThrottling

@Nonnull
static WatermarkEmissionPolicy noThrottling()

Returns a policy that does no throttling: emits each watermark. Since the timestamps are typically quite dense (in milliseconds), this emission policy will pass through many watermark items that have no useful effect in terms of updating the state of accumulating vertices. It is useful primarily in testing scenarios or some specific cases where it is known that no watermark throttling is needed.

emitByMinStep

@Nonnull
static WatermarkEmissionPolicy emitByMinStep(long minStep)

Returns a watermark emission policy that ensures that each emitted watermark's value is at least minStep more than the previous one. This is a general, scenario-agnostic throttling policy.

emitByFrame

@Nonnull
static WatermarkEmissionPolicy emitByFrame(SlidingWindowPolicy wDef)

Returns a watermark emission policy that ensures that the value of the emitted watermark belongs to a frame higher than the previous watermark's frame, as per the supplied WindowDefinition. This emission policy should be employed to drive a downstream processor that computes a sliding/tumbling window (accumulateByFrame() or aggregateToSlidingWindow()).