PHP - Fatal error: Allowed memory size , Ayuda por favor

<?php

class mysql {

    //put your code here

 private $host = 'localhost';

 private $user = 'root';

 private $pass= '...';

 private $db= 'lab06';

 private $mysql;

public function __construct() {

     $this->mysql = new mysql($this->host, $this->user, $this->pass, $this->db);

     if ($this->mysql->connect_errno){

         echo 'se genero el siguiente error al conectar la base de datos: ' . $this->mysql->connect_error;

     }

}

 public function query($_query) {

     return $this->mysql->query($_query);

 }

}