public void reset() {
    if (hasData != null) {
      Arrays.fill(hasData, false);
    }
    if (columnData == null) return;
    for (int i = 0; i < columnData.length; ++i) {
      if (columnData[i] == null) continue;
      for (int j = 0; j < columnData[i].length; ++j) {
        columnData[i][j] = null;
      }
    }
  }
Indicates which columns have data. This is indexed by the column ID in ORC file schema;
the indices that are not included will not have data. Correspond to columnData elements.
storage-api/src/java/org/apache/hadoop/hive/common/io/encoded/EncodedColumnBatch.java