memory problems mysql

I'm having problems updating a mysql database. I want to run this script on a ~800,000 row database but my memory runs out after 5 rows so some how I need to automatically update this mysql query by adding +5 to the LIMIT.

I want to use a redirect or reset the memory somehow..

<?php

    include(dirname(__FILE__) .'/include/simple_html_dom.php');

    mysql_connect('localhost', '', '');
    mysql_select_db('');

    $result = mysql_query("SELECT gamertag FROM gamertags LIMIT 0, 5 ");
        while ($row = mysql_fetch_assoc($result)) {
            $gamertag = $row['gamertag'];

            //pages to pull stats from
            $site_url = 'http://www.bungie.net';
            $stats_page = 'http://www.bungie.net/stats/reach/default.aspx?player=';

            //create dom
            $html = new simple_html_dom();
            $html->load_file($stats_page . urlencode(strtolower($gamertag)));

            //pull nameplate emblem url, ****if it exist****
            $nameplate_emblem_el = $html->find("#ctl00_mainContent_identityBar_namePlateImg");
            if (!$nameplate_emblem_el){
                $nameplate_emblem = 'No nameplate emblem!';
            }
            else{
                //only if #ctl00_mainContent_identityBar_namePlateImg is found
                $nameplate_emblem = htmlspecialchars_decode($nameplate_emblem_el[0]->attr['src开发者_JAVA百科']);
                $nameplate_emblem = $site_url . $nameplate_emblem;
            }   

            mysql_query("INSERT IGNORE INTO star SET gamertag = '".$gamertag."',nameplate = '".$nameplate_emblem."'");
        }

?>

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800.000 is a large number, not sure if it´s gonna happen, but from a comments on php manual: "unset() does just what it's name says - unset a variable. It does not force immediate memory freeing. PHP's garbage collector will do it when it see fits - by intention as soon, as those CPU cycles aren't needed anyway, or as late as before the script would run out of memory, whatever occurs first.

If you are doing $whatever = null; then you are rewriting variable's data. You might get memory freed / shrunk faster, but it may steal CPU cycles from the code that truly needs them sooner, resulting in a longer overall execution time."

source:http://php.net/manual/en/function.unset.php

So, try to unset/set to null the variables after each time the loop runs.

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I'm guessing that you hit your php memory limit, and not the machines. If so, you can edit php.ini (typically /etc/php5/apache2/php.ini) to give more memory to php. Look for "memory_limit = X" where X is something like 256M