Introduction and Installation - Mastering phpMyAdmin 3.1 for Effective MySQL Management - page 19

PersistentConnections
Another important parameter (which is not server-specific but applies to all server
definitions) is $cfg['PersistentConnections'] . For every server we connect to
using the mysql extension, this parameter, when set to TRUE , instructs PHP to keep
the connection to the MySQL server open. This speeds up the interaction between
PHP and MySQL. However, it is set to FALSE by default in config.inc.php because
persistent connections are often a cause of resource depletion on servers. So you
will find MySQL refusing new connections. For this reason, the option is not even
available for the mysqli extension. Hence they setting it to TRUE here would have no
effect if you are connecting with this extension.
connect_type, socket and port
Both the mysql and mysqli extensions automatically use a socket to connect to
MySQL if the server is on localhost . Consider this configuration:
$cfg['Servers'][$i]['host'] = 'localhost';
$cfg['Servers'][$i]['port'] = '';
$cfg['Servers'][$i]['socket'] = '';
$cfg['Servers'][$i]['connect_type'] = 'tcp';
$cfg['Servers'][$i]['extension'] = 'mysql';
The default value for connect_type is tcp . However, the extension will use a socket
because it concludes that this is more efficient as the host is localhost . So in this
case, we can use tcp or socket as the connect_type . To force a real tcp connection,
we can specify 127.0.0.1 instead of localhost in the host parameter. Because the
socket parameter is empty, the extension will try the default socket. If this default
socket, as defined in php.ini , does not correspond to the real socket assigned to the
MySQL server, we have to put the socket name (for example, /tmp/mysql.sock ) in
$cfg['Servers'][$i]['socket'] .
If the hostname is not localhost, a tcp connection will occur—here, on the special port
3307. However, leaving the port value empty would use the default 3306 port:
$cfg['Servers'][$i]['host'] = 'mysql.mydomain.com';
$cfg['Servers'][$i]['port'] = '3307';
$cfg['Servers'][$i]['socket'] = '';
$cfg['Servers'][$i]['connect_type'] = 'tcp';
$cfg['Servers'][$i]['extension'] = 'mysql';