protected void resetColumnArrays(int columnCount) {
    if (hasData != null && columnCount == hasData.length) {
      Arrays.fill(hasData, false);
    } else {
      hasData = new boolean[columnCount];
    }
    ColumnStreamData[][] columnData = new ColumnStreamData[columnCount][];
    if (this.columnData != null) {
      for (int i = 0; i < Math.min(columnData.length, this.columnData.length); ++i) {
        columnData[i] = this.columnData[i];
      }
    }
    this.columnData = columnData;
  }
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