private function displacePush($nextUpdate)
    {
        $query = $this->pdo->prepare(<<<SQL
SELECT
  validUntil,
  UNIX_TIMESTAMP()
FROM robotstxt__cache1
WHERE base = :base;
SQL
        );
        $query->bindValue('base', $this->base, \PDO::PARAM_STR);
        $query->execute();
        if ($query->rowCount() > 0) {
            $row = $query->fetch(\PDO::FETCH_ASSOC);
            $this->clockSyncCheck($row['UNIX_TIMESTAMP()'], self::OUT_OF_SYNC_TIME_LIMIT);
            if ($row['validUntil'] > $row['UNIX_TIMESTAMP()']) {
                $nextUpdate = min($row['validUntil'], $nextUpdate);
                $query = $this->pdo->prepare(<<<SQL
UPDATE robotstxt__cache1
SET nextUpdate = :nextUpdate, worker = 0
WHERE base = :base;
SQL
                );
                $query->bindValue('base', $this->base, \PDO::PARAM_STR);
                $query->bindValue('nextUpdate', $nextUpdate, \PDO::PARAM_INT);
                return $query->execute();
            }
        }
        return false;
    }