title: LAMP stack performance under heavy traffic loads
body: <p>I know the title of my question is rather vague, so I'll try to clarify as much as I can. Please feel free to moderate this question to make it more useful for the community.</p>
  
  <p>Given a standard LAMP stack with more or less default settings (a bit of tuning is allowed, client-side and server-side caching turned on), running on modern hardware (16Gb RAM, 8-core CPU, unlimited disk space, etc), deploying a reasonably complicated CMS service (a Drupal or Wordpress project for arguments sake) - what amounts of traffic, SQL queries, user requests can I resonably expect to accommodate before I have to start thinking about performance?</p>
  
  <p>NOTE: I know that specifics will greatly depend on the details of the project, i.e. optimizing MySQL queries, indexing stuff, minimizing filesystem hits - assuming web developers did a professional job - I'm really looking for a <strong>very rough</strong> figure in terms of visits per day, traffic during peak visiting times, how many records before (transactional) MySQL fumbles, so on.</p>
  
  <p><em>I know the only way to really answer my question is to run load    testing on a real project</em>, and I'm concerned that my question may be treated as partly off-top.</p>
  
  <p>I would like to get a set of figures from people with first-hand experience, e.g. "we ran such and such set-up and it handled at least this much load [problems started surfacing after such and such]". I'm also greatly interested in any <strong>condenced</strong> (I'm short on time atm) reading I can do to get a better understanding of the matter.</p>
  
  <p>P.S. I'm meeting a client tomorrow to talk about his project, and I want to be prepared to reason about performance if his project turns out to be akin FourSquare.</p>