FYI, re-posted in SO: - https://stackoverflow.com/questions/79916913/how-to-ignore-watermarks-for-control-streams
Salva On 2026/03/19 05:57:44 Salva Alcántara wrote: > There are situations where the overall (minimum) watermark for an operator > with multiple inputs might stall because of a slow, almost static, control > stream—or multiple ones. > > There are multiple options that I've seen used/recommended out there: > > 1. Define a watermark generator returning `MAX_WATERMARK` as explained here: > > https://stackoverflow.com/questions/69765403/apache-flink-watermark-does-not-progress-with-broadcast-stream > > > 2. Alternatively/similarly, use `withIdleness`—with a very short period > > 3. Wrap the user defined function using Operator API. E.g., > > ```java > public class SingleWatermarkKeyedCoProcessFunction<K, IN1, IN2, OUT> > extends KeyedCoProcessOperator<K, IN1, IN2, OUT> { > public SingleWatermarkKeyedCoProcessFunction(KeyedCoProcessFunction<K, > IN1, IN2, OUT> flatMapper) { > super(flatMapper); > } > > @Override > public void processWatermark1(Watermark mark) throws Exception { > super.processWatermark(mark); > } > > @Override > public void processWatermark2(Watermark mark) { } > } > ``` > > To me, this looks more like a property of the streams themselves, so I'd be > partial to either 1 or 2—although I've personally used 3 in some projects. > > Maybe it would make sense to add a new generator to cover this use case? > E.g., for option 1: > > ```java > static <A> DocumentWatermarkStrategy<A> ignoreWatermarks() { > return (ctx) -> new IgnoreWatermarksGenerator<>(); > } > ``` > > where: > > ```java > public class IgnoreWatermarksGenerator<T> implements WatermarkGenerator<T> { > @Override > public void onEvent(T event, long eventTimestamp, WatermarkOutput > output) { /* Do nothing */ } > > @Override > public void onPeriodicEmit(WatermarkOutput output) { > output.emitWatermark(Watermark.MAX_WATERMARK); > } > } > ``` > > Any thoughts on this? > Maybe the docs should cover this problem/common pitfall more explicitly? > > Regards, > > Salva >
