From this documentation I can read following:
By default, the record will use the timestamp embedded in Kafka ConsumerRecord as the event time. You can define your own WatermarkStrategy for extract event time from the record itself, and emit watermark downstream:
env.fromSource(kafkaSource, new CustomWatermarkStrategy(), "Kafka Source With Custom Watermark Strategy")This documentation describes details about how to define a WatermarkStrategy.
What Watermark strategy is used if user doesn't provide the optional one?
I'm asking, because I found that default is empty in the source code.
We are running Flink 1.11.