public void initializeForFetch(CompilationOpContext ctx) {
    if (source == null) {
      ListSinkDesc desc = new ListSinkDesc(serializationNullFormat);
      sink = (ListSinkOperator) OperatorFactory.get(ctx, desc);
      source = sink;
    }
  }
Whether this FetchWork is returning a cached query result
ql/src/java/org/apache/hadoop/hive/ql/plan/FetchWork.java