What is a watermark column?
💡 Model Answer
A watermark column is a timestamp field used in streaming data processing to indicate the event time of a record. It helps the system determine when it can safely perform aggregations or windowed computations by marking the point in time up to which all events have been received. For example, in Kafka Streams or Flink, a watermark of "2023-08-01T12:00:00Z" means that the system can close windows that end before that time, assuming no late data will arrive. Watermarks are crucial for handling out-of-order events and ensuring accurate results in real-time analytics.
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