Status

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Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).

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package org.apache.flink.api.connector.sink;
import org.apache.flink.api.common.eventtime.Watermark;

@Experimental
public interface SinkWriter<InputT, CommT, WriterStateT> extends AutoCloseable {

  /**
   * Add a watermark to the writer.
   *
   * @param watermark The watermark.
   * @throws IOException if fail to add a watermark.
   */
  default void writeWatermark(Watermark watermark) throws IOException {}

  void write(InputT element, Context context) throws IOException;
}

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1. Combine a process function and a sink function to achieve similar effects with increased complexity.
2. Introduce event-time timers to sink functions.  This approach seems too element-centric for the use cases.   Also, event-time timers are generally keyed.

Future Enhancements

1. Add support for idleness.  A sink operator may become idled due to upstream status changes.  A future enhancement would be to inform the sink function in this situation.