org.apache.flink.streaming.api.functions

接口 AssignerWithPeriodicWatermarks<T>

类型参数:

T - The type of the elements to which this assigner assigns timestamps.

所有超级接口:

org.apache.flink.api.common.functions.Function, Serializable, TimestampAssigner<T>

所有已知实现类:

AscendingTimestampExtractor, AscendingTimestampExtractor, BoundedOutOfOrdernessTimestampExtractor, IngestionTimeExtractor

public interface AssignerWithPeriodicWatermarks<T>
extends TimestampAssigner<T>

The AssignerWithPeriodicWatermarks assigns event time timestamps to elements, and generates low watermarks that signal event time progress within the stream. These timestamps and watermarks are used by functions and operators that operate on event time, for example event time windows.

Use this class to generate watermarks in a periodical interval. At most every i milliseconds (configured via ExecutionConfig.getAutoWatermarkInterval()), the system will call the getCurrentWatermark() method to probe for the next watermark value. The system will generate a new watermark, if the probed value is non-null and has a timestamp larger than that of the previous watermark (to preserve the contract of ascending watermarks).

The system may call the getCurrentWatermark() method less often than every i milliseconds, if no new elements arrived since the last call to the method.

Timestamps and watermarks are defined as longs that represent the milliseconds since the Epoch (midnight, January 1, 1970 UTC). A watermark with a certain value t indicates that no elements with event timestamps x, where x is lower or equal to t, will occur any more.

另请参阅:

Watermark

方法概要

限定符和类型	方法和说明
Watermark	getCurrentWatermark() Returns the current watermark.

从接口继承的方法 org.apache.flink.streaming.api.functions.TimestampAssigner

extractTimestamp

方法详细资料

getCurrentWatermark

@Nullable
Watermark getCurrentWatermark()

Returns the current watermark. This method is periodically called by the system to retrieve the current watermark. The method may return null to indicate that no new Watermark is available.

The returned watermark will be emitted only if it is non-null and its timestamp is larger than that of the previously emitted watermark (to preserve the contract of ascending watermarks). If the current watermark is still identical to the previous one, no progress in event time has happened since the previous call to this method. If a null value is returned, or the timestamp of the returned watermark is smaller than that of the last emitted one, then no new watermark will be generated.

The interval in which this method is called and Watermarks are generated depends on ExecutionConfig.getAutoWatermarkInterval().

返回:

Null, if no watermark should be emitted, or the next watermark to emit.

另请参阅:

Watermark, ExecutionConfig.getAutoWatermarkInterval()