// if there are any changes update product in database
if ($price != $product->getPrice() OR $availability != $product->getAvailability() OR $action != $product->getAction()) {
    if ($product->update($price, $availability, $action)) {
        $log['success'][] = $product->getName();
    } else {
        $log['error'][] = $product->getName();
    }
} else {
    $log['unchanged'][] = $product->getName();
}