WatermarkFunction (samza-api 1.9.0-SNAPSHOT API)
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org.apache.samza.operators.functions
Interface WatermarkFunction<T>
public interface WatermarkFunction<T>
Allows handling of watermarks.
Method Summary
All Methods Instance Methods Abstract Methods 
Modifier and Type
Method and Description
java.lang.Long
getOutputWatermark()
Returns the output watermark.
java.util.Collection<T>
processWatermark(long watermark)
Processes the input watermark coming from upstream operators.
Method Detail
processWatermark
java.util.Collection<T> processWatermark(long watermark)
Processes the input watermark coming from upstream operators.
This allows custom watermark handling, such as triggering events or propagating it downstream.
Parameters:
watermark - input watermark
Returns:
output triggered after processing the watermark
getOutputWatermark
java.lang.Long getOutputWatermark()
Returns the output watermark. This function will be invoked immediately after either
of the following events:
Return from the transform function, e.g. FlatMapFunction.
Return from the processWatermark(long) function.
Note: If the transform function returns a collection of messages, the output watermark
will be emitted after the output collection has been propagated to downstream operators.
This might delay the watermark propagation, which will cause more buffering and might
have a performance impact.
Returns:
output watermark, or null if the output watermark should not be updated.
Samza guarantees that the same watermark value will only be emitted once.
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