Question

I am working on a subquery library for CodeIgniter (link to project), which works by returning database objects that you can use instead of the normal $this->db object.

Originally, I was making new database objects each time:

$this->CI =& get_instance();
$db = $this->CI->load->database('', true);

But I then realized (or rather someone pointed out to me) that this would make a new database connection each time! So I decided to try to clone objects instead of making new ones.

I updated the code to look like so (link to full code):

class Subquery{
    var $CI, $db;

    function __construct(){
        $this->CI =& get_instance();
        $this->db = $this->CI->db; // Default database connection
    }

    function start_subquery(){
        $newDatabase = clone $this->db;
        // some more code
        return $newDatabase;
    }
}

I tested this, and it seems to work, but I’m not sure if this solves the problem. Does using clone make a new database connection, or does it use references internally and only keep one connection?

Answer 1

First off, the =& is unnecessary and potentially harmful if you are not using PHP 4 (I assume get_instance returns an object).

As for whether clone creates a new connection .. this depends on the DB implementation. As far as I can tell, PDO does not create an additional connection when it’s cloned. If you want to test this, create a small script that runs start_subquery to some effect and then sleeps for a decent amount of time. Connect to mysql and run:

SHOW STATUS WHERE `variable_name` = 'Threads_connected'

If it’s more than 2 (your connection to run the query and the one from your script) then an additional connection is being made for some reason.

As for whether you should clone the DB, I don’t know why you would want to, but I don’t really know the use case for this class nor do I know much about CI.