code: public void setCosts(Costs nodeCosts) {
  		// the plan enumeration logic works as for regular two-input-operators, which is important
  		// because of the branch handling logic. it does pick redistributing network channels
  		// between the sink and the sink joiner, because sinks joiner has a different DOP than the sink.
  		// we discard any cost and simply use the sum of the costs from the two children.
  		
  		Costs totalCosts = getInput1().getSource().getCumulativeCosts().clone();
  		totalCosts.addCosts(getInput2().getSource().getCumulativeCosts());
  		super.setCosts(totalCosts);
  	}
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