phppdo

PDO MySQL Connection close - unset vs null

I've read in PDO manual that to close connection you should use the following:

$connection = null;

However, Some people suggested that since PHP 5.3 has a new GC, the following should be used:

unset($connection);

I need to know once and for all, which one is preferred, or are they the same?

Solution

  • They do the same thing. Unsetting the $pdo handle and setting it null both close the connection.

    You can test this for yourself. Run the following script in one window, and in a second window open the MySQL client and run SHOW PROCESSLIST every couple of seconds to see when the connection disappears.

    <?php

$pdo = new PDO(..);
sleep(10);
unset($pdo);
echo "pdo unset!\n";
sleep(10);

    Then change unset($pdo) to $pdo=null; and run the test again.

    <?php

$pdo = new PDO(..);
sleep(10);
$pdo = null;
echo "pdo set null!\n";
sleep(10);

    The extra sleep() at the end is there to give you a moment to see that the connection has dropped, before the PHP script terminates (which would drop the connection anyway).