org.apache.flink.streaming.api.watermark

Class Watermark

java.lang.Object

org.apache.flink.streaming.runtime.streamrecord.StreamElement

org.apache.flink.streaming.api.watermark.Watermark

@PublicEvolving
public final class Watermark
extends StreamElement

A Watermark tells operators that no elements with a timestamp older or equal to the watermark timestamp should arrive at the operator. Watermarks are emitted at the sources and propagate through the operators of the topology. Operators must themselves emit watermarks to downstream operators using Output.emitWatermark(Watermark). Operators that do not internally buffer elements can always forward the watermark that they receive. Operators that buffer elements, such as window operators, must forward a watermark after emission of elements that is triggered by the arriving watermark.

In some cases a watermark is only a heuristic and operators should be able to deal with late elements. They can either discard those or update the result and emit updates/retractions to downstream operations.

When a source closes it will emit a final watermark with timestamp Long.MAX_VALUE. When an operator receives this it will know that no more input will be arriving in the future.

Field Summary

Fields

Modifier and Type	Field and Description
static Watermark	MAX_WATERMARK The watermark that signifies end-of-event-time.
static Watermark	UNINITIALIZED The watermark that signifies is used before any actual watermark has been generated.

Constructor Summary

Constructors

Constructor and Description
Watermark(long timestamp) Creates a new watermark with the given timestamp in milliseconds.

Method Summary

Modifier and Type	Method and Description
boolean	equals(Object o)
long	getTimestamp() Returns the timestamp associated with this Watermark in milliseconds.
int	hashCode()
String	toString()

Methods inherited from class org.apache.flink.streaming.runtime.streamrecord.StreamElement

asLatencyMarker, asRecord, asStreamStatus, asWatermark, isLatencyMarker, isRecord, isStreamStatus, isWatermark

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

MAX_WATERMARK

public static final Watermark MAX_WATERMARK

The watermark that signifies end-of-event-time.

UNINITIALIZED

public static final Watermark UNINITIALIZED

The watermark that signifies is used before any actual watermark has been generated.

Constructor Detail

Watermark

public Watermark(long timestamp)

Creates a new watermark with the given timestamp in milliseconds.

Method Detail

getTimestamp

public long getTimestamp()

Returns the timestamp associated with this Watermark in milliseconds.

equals

public boolean equals(Object o)

Overrides:

equals in class Object

hashCode

public int hashCode()

Overrides:

hashCode in class Object

toString

public String toString()

Overrides:

toString in class Object