PHP xmlReader：何时打开和关闭

Have a very large xml data feed I am parsing in PHP so Im using xmlReader because simpleXML fails everytime - just locks up and stops. Even with an xmlReader/simpleXML hybrid code, it still fails so Im doing it all in xmlReader - unfortunately.

So, Im confused on where to open and close xmlReader in relation to my loops. I need the best memory managment possible.

****Open reader Here????

Foreach ($modelArray as $model)// there are 10000 models

****OR open reader Here???

    if(!$reader->open($request_url)){
        echo "Error";
        break;
    }
    while ($reader->readToNext('Product'){ // There are 500 Products  per model
       //do my node processing here. Grab nodes and add to mysql DB
    }

    return array('msg' => $msg,'addedProdsPerManu' =>$counter_addedProdsManu);

****Close Reader HERE?

}//close foreach

****OR Close Reader HERE?

Any advice would be greatly appreciated for the most efficient memory utilization so this program will run all the way through.

Thank you

Comments below between /** */

/**
 * If you can, open it here.
 */

Foreach ($modelArray as $model)// there are 10000 models

    /**
     * If you open the reader here, you are doing 10000 network requests.
     *
     * BUT depends on your needs, if the url must be get from the model, you'll
     * have to connect here.
     */
    if(!$reader->open($request_url)){
        echo "Error";
        break;
    }

    while ($reader->readToNext('Product'){ // There are 500 Products  per model
       //do my node processing here. Grab nodes and add to mysql DB
    }

    /**
     * IF you opened the connection just before the while, THEN close it here.
     */

    /**
     * return HERE!?? 
     * You're just checking the first model then!!
     */        
    return array('msg' => $msg,'addedProdsPerManu' =>$counter_addedProdsManu);

}//close foreach

/**
 * If you could open the connection before the foreach, then close it here.
 */