Error Establishing Connection To Database.

Hey guys i got a problem i made update to my wordpress to 3.9.1 and i have a big problem.

Since i made the problem if on my blog there ar more then 80 100 people online wordpress starts to display theath is not able to connect to database till someone quits the website after if i hit refresh it starts to work i had contacted even cpanel/cloudlinux …etc because im the owner of the dedicated server and nothink.

Before making the update i was allwais having 1000 online and the problem was not showing.

So what i was thinking i put this code in wp-config

$link = mysql_connect('localhost', 'dbuser', 'mypass');
if (!$link) {
die('Could not connect: ' . mysql_error());
}

And the problem was not showing any more.

If i`m removing the code it starts again.

I had made a fresh reinstall of the wordpress and i had optimized the database because i was thinking sompting is wrong and still the same problem if i remove the code belong from wp-config.