We are running a major website using two VPSs, one for the website and the other as de DB server. Ever since we went live (two days ago) the CPU load on the DB VPS is extremely high reaching 100% and the total load over 10.
As a result the website is very, very slow although before we went live (open to the public) we tested everything for over two months.
There is plenty RAM and HD space, and we believe the programming and indexing of the website is correct, although it would hurt to have someone who could optimize MySQL and also look at the DB structure.
Software used: Our own CMS using LAMP, PHP and MySQL 5, OOP and Ajax.