code: protected ColumnFamily cleanExpired(ColumnFamily columnFamily, long timestamp) {
          ColumnFamily cleanColumnFamily = ArrayBackedSortedColumns.factory.create(baseCfs.metadata);
          for (Cell cell : columnFamily) {
              if (cell.isLive(timestamp)) {
                  cleanColumnFamily.addColumn(cell);
              }
          }
          return cleanColumnFamily;
      }
docs: Returns a {@link ColumnFamily} composed by the non expired {@link Cell}s of the specified  {@link ColumnFamily}.
  
  @param columnFamily A {@link ColumnFamily}.
  @param timestamp    The max allowed timestamp for the {@link Cell}s.
  @return A {@link ColumnFamily} composed by the non expired {@link Cell}s of the specified  {@link ColumnFamily}.