code: public DataSink<T> setParallelism(int parallelism) {
  		Preconditions.checkArgument(parallelism > 0 || parallelism == ExecutionConfig.PARALLELISM_DEFAULT,
  			"The parallelism of an operator must be at least 1.");
  
  		this.parallelism = parallelism;
  
  		return this;
  	}
docs: Sets the parallelism for this data sink.
  The degree must be 1 or more.
  
  @param parallelism The parallelism for this data sink. A value equal to {@link ExecutionConfig#PARALLELISM_DEFAULT}
  will use the system default.
  @return This data sink with set parallelism.