Package org.apache.flink.streaming.runtime.operators.util

Interface WatermarkStrategyWithPunctuatedWatermarks<T>

Type Parameters:
T - The type of the elements to which this assigner assigns timestamps.
All Superinterfaces:
Serializable, org.apache.flink.api.common.eventtime.TimestampAssigner<T>, org.apache.flink.api.common.eventtime.TimestampAssignerSupplier<T>, org.apache.flink.api.common.eventtime.WatermarkGeneratorSupplier<T>, org.apache.flink.api.common.eventtime.WatermarkStrategy<T>
@Internal public interface WatermarkStrategyWithPunctuatedWatermarks<T> extends org.apache.flink.api.common.eventtime.WatermarkStrategy<T>, org.apache.flink.api.common.eventtime.TimestampAssigner<T>
The AssignerWithPunctuatedWatermarks 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 if certain special elements act as markers that signify event time progress, and when you want to emit watermarks specifically at certain events. 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).

For use cases that should periodically emit watermarks based on element timestamps, use the WatermarkStrategyWithPeriodicWatermarks instead.

The following example illustrates how to use this timestamp extractor and watermark generator. It assumes elements carry a timestamp that describes when they were created, and that some elements carry a flag, marking them as the end of a sequence such that no elements with smaller timestamps can come anymore. 


 public class WatermarkOnFlagAssigner implements AssignerWithPunctuatedWatermarks<MyElement> {

     public long extractTimestamp(MyElement element, long previousElementTimestamp) {
         return element.getSequenceTimestamp();
     }

     public Watermark checkAndGetNextWatermark(MyElement lastElement, long extractedTimestamp) {
         return lastElement.isEndOfSequence() ? new Watermark(extractedTimestamp) : null;
     }
 }

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.

See Also:

  • Nested Class Summary

    Nested classes/interfaces inherited from interface org.apache.flink.api.common.eventtime.TimestampAssignerSupplier

    org.apache.flink.api.common.eventtime.TimestampAssignerSupplier.Context, org.apache.flink.api.common.eventtime.TimestampAssignerSupplier.SupplierFromSerializableTimestampAssigner<T extends Object>

    Nested classes/interfaces inherited from interface org.apache.flink.api.common.eventtime.WatermarkGeneratorSupplier

    org.apache.flink.api.common.eventtime.WatermarkGeneratorSupplier.Context

  • Field Summary

    Fields inherited from interface org.apache.flink.api.common.eventtime.TimestampAssigner

    NO_TIMESTAMP

  • Method Summary

    Modifier and Type
    Method
    Description
    Watermark
    checkAndGetNextWatermark(T lastElement, long extractedTimestamp)
    Asks this implementation if it wants to emit a watermark.
    default org.apache.flink.api.common.eventtime.TimestampAssigner<T>
    createTimestampAssigner(org.apache.flink.api.common.eventtime.TimestampAssignerSupplier.Context context)
     
    default org.apache.flink.api.common.eventtime.WatermarkGenerator<T>
    createWatermarkGenerator(org.apache.flink.api.common.eventtime.WatermarkGeneratorSupplier.Context context)
     

    Methods inherited from interface org.apache.flink.api.common.eventtime.TimestampAssigner

    extractTimestamp

    Methods inherited from interface org.apache.flink.api.common.eventtime.WatermarkStrategy

    getAlignmentParameters, withIdleness, withTimestampAssigner, withTimestampAssigner, withWatermarkAlignment, withWatermarkAlignment

  • Method Details

    • checkAndGetNextWatermark

      @Nullable Watermark checkAndGetNextWatermark(T lastElement, long extractedTimestamp)
      Asks this implementation if it wants to emit a watermark. This method is called right after the TimestampAssigner.extractTimestamp(Object, long) method.

      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 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.

      For an example how to use this method, see the documentation of this class.

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

    • createTimestampAssigner

      default org.apache.flink.api.common.eventtime.TimestampAssigner<T> createTimestampAssigner(org.apache.flink.api.common.eventtime.TimestampAssignerSupplier.Context context)
      Specified by:
      createTimestampAssigner in interface org.apache.flink.api.common.eventtime.TimestampAssignerSupplier<T>
      Specified by:
      createTimestampAssigner in interface org.apache.flink.api.common.eventtime.WatermarkStrategy<T>

    • createWatermarkGenerator

      default org.apache.flink.api.common.eventtime.WatermarkGenerator<T> createWatermarkGenerator(org.apache.flink.api.common.eventtime.WatermarkGeneratorSupplier.Context context)
      Specified by:
      createWatermarkGenerator in interface org.apache.flink.api.common.eventtime.WatermarkGeneratorSupplier<T>
      Specified by:
      createWatermarkGenerator in interface org.apache.flink.api.common.eventtime.WatermarkStrategy<T>