Github user mjsax commented on the pull request:

    https://github.com/apache/flink/pull/983#issuecomment-127605738
  
    I used different dop for source/consumer and double check that multiple TMs 
are involved to make sure data is really going over the network...
    
    Batch example:
    ```
    public class TestEmptyTupleBatch {
    
        public static void main(String[] args) throws Exception {
                final ExecutionEnvironment env = 
ExecutionEnvironment.getExecutionEnvironment();
    
                DataSource<Tuple0> input = env.fromElements(
                                new Tuple0(), new Tuple0(), new Tuple0(), new 
Tuple0(), new Tuple0(),
                                new Tuple0(), new Tuple0(), new Tuple0(), new 
Tuple0(), new Tuple0(),
                                new Tuple0(), new Tuple0(), new Tuple0(), new 
Tuple0(), new Tuple0(),
                                new Tuple0(), new Tuple0(), new Tuple0(), new 
Tuple0(), new Tuple0());
    
                input.map(new Counter()).setParallelism(4).print();
        }
    
        public static class Counter implements MapFunction<Tuple0, Integer> {
                private static final long serialVersionUID = 
5518823010274195186L;
    
                int counter = 0;
                @Override
                public Integer map(Tuple0 value) throws Exception {
                        System.out.println("mjsax: " + (++counter) + " " + 
value.getField(0));
                        return new Integer(value.getArity());
                }
        }
    }
    ```
    
    Streaming Example:
    ```
    public class TestEmptyTuple {
    
        public static void main(String[] args) throws Exception {
                final StreamExecutionEnvironment env = 
StreamExecutionEnvironment.getExecutionEnvironment();
    
                DataStream<Tuple0> input = env.addSource(new 
Empty()).setParallelism(4);
                input.shuffle().transform("verify", null, new 
Counter()).setParallelism(1);
    
                env.execute();
        }
    
        public static class Empty implements ParallelSourceFunction<Tuple0> {
                private static final long serialVersionUID = 
1350902748274781033L;
                private volatile boolean isRunning = true;
    
                @Override
                public void 
run(org.apache.flink.streaming.api.functions.source.SourceFunction.SourceContext<Tuple0>
 ctx)
                                                throws Exception {
                        while (this.isRunning) {
                                Thread.sleep(1000);
                                ctx.collect(new Tuple0());
                        }
                }
    
                @Override
                public void cancel() {
                        this.isRunning = false;
                }
        }
    
        public static class Counter implements 
OneInputStreamOperator<Tuple0,Object> {
                private static final long serialVersionUID = 
5518823010274195186L;
    
                private int counter = 0;
                @Override
                public void processElement(StreamRecord<Tuple0> element) throws 
Exception {
                        System.out.println("Tuple0: " + (++counter));
                }
    
                // 
        }
    
    }
    ```
    



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