@Override
    public RelDistribution getDistribution(HiveJoin join) {
      return HiveAlgorithmsUtil.getJoinRedistribution(join.getJoinPredicateInfo());
    }
COMMON_JOIN is Sort Merge Join. Each parallel computation handles multiple
splits.
ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/cost/HiveOnTezCostModel.java