@Override
          public int compare(OperatorBucketingVersionInfo i1, OperatorBucketingVersionInfo i2) {
            int r = i1.infoType.compareTo(i2.infoType);
            if (r != 0) {
              // mandatory first
              return r;
            }
            r = Integer.compare(i2.bucketingVersion, i1.bucketingVersion);
            if (r != 0) {
              // prefer higher version if avail
              return r;
            }
            r = i1.op.toString().compareTo(i2.op.toString());
            return r;
          }
This class represents the version required by an Operator.
ql/src/java/org/apache/hadoop/hive/ql/optimizer/BucketVersionPopulator.java