Update/insert in chunks?

[eluser]codex[/eluser]
The code. Maybe you can spot something wrong here.

Code:

function copy_temp_to_live($feed_id)
    {
        // First get data from temp
        $this->CI->db->group_by('pId'); // GROUP BY to ignore duplicates
        $query = $this->CI->db->get('products_temp');
        
        if ($query->num_rows() > 0)
        {
            // WE HEBBEN TEMP PRODUCTEN!
            // Temp products
            $res = $query->result_array();
            
            // Get products
            $this->CI->db->where('pFeedId', 11);
            $query2 = $this->CI->db->get('products');
            
            if ($query2->num_rows() > 0)
            {
                // WE HEBBEN PRODUCTEN!
                $new = $query2->result_array();
                
                // Stop in array
                foreach($new as $n) // products
                {
                    $arr[] = $n['pId'];
                }
            
                foreach($res as $r)
                {
                    if (in_array($r['pId'], $arr))
                    {
                        // The id already exists in the db
                        // Update with new data
                        if (($n['pTitle'] != $r['pTitle'])    
                                or ($n['pUrl']             != $r['pUrl'])
                                or ($n['pDescription']     != $r['pDescription'])
                                or ($n['pImgSmall']     != $r['pImgSmall'])
                                or ($n['pImgLarge']     != $r['pImgLarge'])
                                or ($n['pPrice']         != $r['pPrice'])
                                or ($n['pPriceOld']     != $r['pPriceOld'])
                                )
                        {
                            $update = array('pUrl'                 => $r['pUrl'],
                                            'pTitle'             => $r['pTitle'],
                                            'pTitleUrlSafe'     => normalize_string($r['pTitle'], '-'),
                                            'pDescription'         => $r['pDescription'],
                                            'pDescription2'     => $r['pDescription2'],
                                            'pImgSmall'         => $r['pImgSmall'],
                                            'pImgLarge'         => $r['pImgLarge'],
                                            'pPrice'             => $r['pPrice'],
                                            'pPriceOld'         => $r['pPriceOld'],
                                            'pCategory'         => $r['pCategory'],
                                            'pCategoryPath'     => $r['pCategoryPath'],
                                            'pSubCategory'        => $r['pSubCategory'],
                                            'pSubCategoryPath'     => $r['pSubCategoryPath'],
                                            'pStock'             => $r['pStock'],
                                            'pPriceShipping'    => $r['pPriceShipping'],
                                            'pTimeToShip'         => $r['pTimeToShip'],
                                            'pEAN'                 => $r['pEAN']
                                            );
                        
                            $this->CI->db->where('pId', $r['pId']);
                            $this->CI->db->update('products', $update);
                        }
                    }