org.apache.samza.operators.functions

Interface WatermarkFunction<T>

public interface WatermarkFunction<T>

Allows handling of watermarks.

Method Summary

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:

1. Return from the transform function, e.g. FlatMapFunction.
2. 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.