@Explain(vectorization = Vectorization.SUMMARY, displayName = "enableConditionsMet",
        explainLevels = { Level.DEFAULT, Level.EXTENDED })
    public List<String> getEnableConditionsMet() {
      if (mergeWorkVectorizationConditions == null) {
        mergeWorkVectorizationConditions = createMergeWorkExplainVectorizationConditions();
      }
      return VectorizationCondition.getConditionsMet(mergeWorkVectorizationConditions);
    }
For now, this class just says in EXPLAIN VECTORIZATION we don't support vectorization of the
Merge Join vertex instead of being silent about it.
ql/src/java/org/apache/hadoop/hive/ql/plan/MergeJoinWork.java