private static boolean isValidProbeDecodeMapJoin(MapJoinOperator mapJoinOp) {
    Map<Byte, List<ExprNodeDesc>> keyExprs = mapJoinOp.getConf().getKeys();
    List<ExprNodeDesc> bigTableKeyExprs = keyExprs.get( (byte) mapJoinOp.getConf().getPosBigTable());
    return (bigTableKeyExprs.size() == 1) && (bigTableKeyExprs.get(0) instanceof ExprNodeColumnDesc);
  }
Returns true for a MapJoin operator that can be used for ProbeDecode.
MapJoin should be a single Key join, where the bigTable keyCol is only a ExprNodeColumnDesc
@param mapJoinOp
@return true for a valid MapJoin
ql/src/java/org/apache/hadoop/hive/ql/parse/TezCompiler.java