Setting a connect timeout with PDO
$DBH = new PDO( "mysql:host=$host;dbname=$dbname", $username, $password, array( PDO::ATTR_TIMEOUT => 5, // in seconds PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION ));
I'm using the DBLIB driver for PDO - and that doesn't support the passing of options (throws a warning).
To get round this, you can edit the connection_timeout setting in the FreeTDS config file which is located at /etc/freetds/freetds.conf (on Ubuntu).