Recently my company's site has been experiencing a much higher level of traffic, with daily visitors rising from 4k to 18k. While under heavy load our site runs extremely slow. We are currently within the most important week of the year for our company and we need this fixed right away.
A couple months ago we had the same problems with 4k daily visitors and hired a freelancer to solve the problem, which he did at the time, but now it has returned. We are running the W3 cache, upgraded from a 1gb to 2gb dedicated virtual server on Media Temple (although we can't see a difference), had php and apache recompiled but still can not find the root of the problem.
Perhaps the solution is through apache and php tuning? There are many php errors in the logs that need to be addressed. The issue is quite urgent and the sooner is it resolved, the better.
Thank you for your bids and please PM with what strategy you would take.