I have seen many posts relating to both of the issues above, and I'm not sure if posting my fix here is the right place, but so many seem to have these issues that I have to share

1. Problem Description
======================
a. Both admin and front-end respond slowly to any request for a page - important: time how long it takes!
b. When a user has at least 1 item in their cart, go to the shopping cart and, within the time from above, and as quickly as you can, hit "Continue Shopping". A browser dialog with the contents: "error" appears. When you click OK, the requested page loads without error, but still as slowly as all the others. Tested with:
On WIN: IE9, FireFox 29, Chrome 35, Opera 22 - ONLY IE9 did NOT show the error
On MAC: Safari 7.0.3, Firefox 29, Chrome 35, Opera 22 - ALL browsers showed the error
2. My Situation
===============
My ISP had (they think) name resolution issues between the server hosting the php and the server hosting the MySQL database.
3. Their fix
============
Modify config.php and change:
define('DB_HOSTNAME', '<your.fully.qualified.hostname>');
to:
define('DB_HOSTNAME', '<IP Address>'); //in my case, I needed 127.0.0.1
Note: angle brackets above indicate substitution information, DO NOT LEAVE THEM THERE!
4. Verification
===============
If this was also your situation, page loads should be heaps faster. When you try step 1b above, you can't click "Continue Shopping" fast enough to bring up the error!

5. TIP
======
If you use phpMyAdmin. it will also be faster if you modify its configuration:
in config.inc.php change the value of this line: $cfg['Servers'][$i]['host'] = '<IP Address>';
Test response of phpMyAdmin AFTER you log into it!
Regards, Chris.
P.S. I don't know how to mark this as [RESOLVED] to alert others when searching, sorry
