public int getColumnsWithDataCount() {
      int childCount = hasData.length, result = 0;
      for (int childIx = 0; childIx < childCount; ++childIx) {
        if (!hasData(childIx) && !hasVectors(childIx)) continue;
        ++result;
      }
      return result;
    }
Same as columnData, but for the data that already comes as VRBs.
The combination of the two contains all the necessary data,
ql/src/java/org/apache/hadoop/hive/ql/io/orc/encoded/Reader.java