public function clean()
    {
        $this->assertReady();
        
        $sql = sprintf("DELETE FROM %s WHERE %s < NOW() - INTERVAL %d SECOND",
            $this->dbAdapter->platform->quoteIdentifier($this->table),
            $this->dbAdapter->platform->quoteIdentifier($this->timestampColumn),
            $this->getCleanInterval()->toSeconds());
        
        $this->dbAdapter->query($sql, DbAdapter::QUERY_MODE_EXECUTE);
    }