What is a good/healthy mysql query execution time? What is a good/healthy mysql query execution time?

To my calculations:


  The site gets 1000 unique visitors per hr
  
  10 page view for each unique visitor
  
  5 minutes for each unique visitor (I'm ignoring this. I should,
  right?)
  
  1000*10=10000/(60*60) = 2.7 views per second.
  
  I have 3 queries on every page. 2.7*3 = 8.1 queries per second
  
  1 second/8.1 = 0.123


So average query execution time must be less than 0.123. 

Assuming visits don't increase, can we say anything less than 0.123 works for a healthy database?
The question is a bit vague, but I think this answer (a) may provide some useful guidance and (b) is too big to fit in a comment.

Capacity planning a server is a bit more complex than that.  You need to take some basic queuing theory into account.  Your model would describe a server at 100% capacity, which is actually likely to cause performance issues.  In practice you would want to aim for the server running perhaps 25-50% capacity at peak load if you want your site to have consistent response times.

Queuing models state that the average wait time increases hyperbolically as the system approaches saturation. 


A system that is 50% saturated has two requests waiting service on average
A system that is 90% saturated has 10 queued requests on average
A system that is 99% saturated has 100 queued requests on average


You should benchmark your queries under load to see how much resource they actually take up.  Then apply a view of your peak load to see how much capacity you need for the system to remain responsive.