PHP generate XML with large database.

XMLFeed.php

class XMLFeed
{
	private $xmlHeader = '<products>';
	private $xmlFooter = '</products>';
	private $xmlFeedFile = 'products.xml';

	public function feed()
	{
		$offeset = 0;
		$perLoop = 1000;

		$xmlFile = fopen($this->xmlFeedFile, 'w');

		fwrite($xmlFile, $this->xmlHeader);

		for ($i = 0; $i < 20; $i++)
		{
			$offeset = $i * $perLoop;

			$sql = "SELECT id, name, price, category FROM product "
			. "LEFT JOIN category ON product.category_id = category.id "
			. "LIMIT " . $offeset . "," . $perLoop;
			$query = mysql_query($sql);
			$products = mysql_fetch_assoc($query);

			foreach ($products as $product)
			{
				$xml = '<product>';
				$xml .= '<id>' . $product->id . '</id>';
				$xml .= '<name>' . $product->name . '</name>';
				$xml .= '<price>' . $product->price . '</price>';
				$xml .= '<category>' . $product->category . '</category>';
				$xml .= '</product>';
			}

			fwrite($xmlFile, $xml);
		}

		fwrite($xmlFile, $this->xmlFooter);
		fclose($xmlFile);
	}
}