Magento memory leak in for loop - php

Question

I can't figure out where all my memory is going, memory gets exhausted after about 28,000 loops. have tried several combinations of unset to no avail.
updateProduct() is only commented out to help me isolate the issue.
Any help would be appreciated.
include_once '../app/Mage.php';
Mage::init();
//fetch all products
$res = Mage::getSingleton('core/resource');
$db = $res->getConnection('catalog_read');
$productTable = $res->getTableName('catalog/product');
$sql = $db->select()->from($productTable,
'entity_id'
);
//Returns about 162,000 rows
$rows = $db->fetchAll($sql);
$rowcount = count($rows);
$progress = 0;
foreach($rows as $productRow)
{
$product_id = $productRow["entity_id"];
if($product_id){
//memory leaks here.
$product=Mage::getModel('catalog/product')->setStoreID(0)->load($product_id);
//updateProduct($product);
}else{
echo "LOAD ERROR\n";
}
$product->clearInstance();
unset($product);
gc_collect_cycles();
//echo memory_get_usage() . " 49\n";
if($progress % 500 == 0)
{
echo "$progress out of $rowcount complete\n";
echo memory_get_usage() . "\n";
}
$progress++;
}
updateProduct is matching discount to some layered navigation attributes:
function updateProduct($product_id)
{
global $off10,$off20,$off30,$off40,$off50;
//echo "$product_id\n";
$product=Mage::getModel('catalog/product')->setStoreID(0)->load($product_id);
$attribute = $product->getResource()->getAttribute('discount');
if ($attribute)
{
$discount_value += $attribute->getFrontend()->getValue($product);
//Match discount to layered_nav_discount and all attributes < discount
if($discount_value < 10){
$value = "";
}elseif($discount_value < 20){
$value = "$off10";
}elseif($discount_value < 30){
$value = "$off10,$off20";
}elseif($discount_value < 40){
$value = "$off10,$off20,$off30";
}elseif($discount_value < 50){
$value = "$off10,$off20,$off30,$off40";
}elseif($discount_value >= 50){
$value = "$off10,$off20,$off30,$off40,$off50";
}
//Update layered_nav_discount
//$_product->addAttributeUpdate('layered_nav_discount', $value, 0);
unset($product);
return;
}
};

Answer 1

You can add in top of file for increase memory and time limit.
set_time_limit(0);
ini_set('memory_limit','512M');