private function fetchDistinctDate($table)
 {
     $dar = $this->disk_usage_dao->retrieve("SELECT distinct date FROM {$table} ORDER BY date");
     $dates = array();
     foreach ($dar as $row) {
         $date = explode(' ', $row['date']);
         $dates[] = $date[0];
     }
     return $dates;
 }
 private function fetchOldestDate($table)
 {
     return $this->disk_usage_dao->searchOldestDate($table);
 }