I initially thought that the order of the watermarks could be altered because of the keying, but I eventually read somewhere that watermarks are broadcast downstream, so I think what I was thinking isn't relevant.
Regards, Alexis. Am Do., 6. Nov. 2025 um 15:27 Uhr schrieb David Anderson < [email protected]>: > It is customary to do the watermarking as early as possible in the > pipeline, and since FLIP-27 best practice has been to have the sources > apply the watermark strategy. As the documentation [1] points out: > > > There are two places in Flink applications where a WatermarkStrategy can > be used: 1) directly on sources and 2) after non-source operation. The > first option is preferable, because it allows sources to exploit knowledge > about shards/partitions/splits in the watermarking logic. Sources can > usually then track watermarks at a finer level and the overall watermark > produced by a source will be more accurate. > > Why are you thinking it would be preferable to do the keyed partitioning > first? > > That said, I believe what you have proposed will work. > > Best, > David > > [1] > https://nightlies.apache.org/flink/flink-docs-stable/docs/dev/datastream/event-time/generating_watermarks/#using-watermark-strategies > > > On Tue, Oct 28, 2025 at 1:38 AM Alexis Sarda-Espinosa < > [email protected]> wrote: > >> Hello, >> >> I'm investigating switching our windowing to event time, and I figured it >> would be good to assign timestamps/watermarks *after* the keyBy we need >> for the windows. However, I see the keyBy method instantiates a >> PartitionTransformation whose Javadoc states: "This does not create a >> physical operation, it only affects how upstream operations are connected >> to downstream operations." >> >> So the question is, if I have a DataStream and I define the job like this: >> >> var watermarked = stream.keyBy(...) >> .assignTimestampsAndWatermarks(...) >> >> DataStreamUtils.reinterpretAsKeyedStream(watermarked, ...) >> .window(...) >> >> Is this actually working as expected? >> >> Regards, >> Alexis. >> >
