public static void initUnionPlan(GenMRProcContext opProcCtx, UnionOperator currUnionOp,
      Task<?> currTask, boolean local)
      throws SemanticException {
    // In case of lateral views followed by a join, the same tree
    // can be traversed more than one
    if (currUnionOp != null) {
      GenMRUnionCtx uCtx = opProcCtx.getUnionTask(currUnionOp);
      assert uCtx != null;
      setUnionPlan(opProcCtx, local, currTask, uCtx, false);
    }
  }
Initialize the current union plan.

@param op
         the reduce sink operator encountered
@param opProcCtx
         processing context
ql/src/java/org/apache/hadoop/hive/ql/optimizer/GenMapRedUtils.java