I'm currently assessing Google App Engine, and one of the answers from Hidden limitations of Google App Engine? stated:Performance will surprise you. GAE is  optimized for many tiny queries and  you get warned if a query takes any  CPU time at all. You get 6.5 (at last  check) free hours per day, but it's a  mystical number and you should test.You'll find that time as you measure  it doesn't relate to the CPU or  datastore CPU time, because (for  example) under the covers there might  be multiple machines updating indexes  during deletes/updates. Some users  have found huge CPU usage when  uploading bulk data - many hours of  usage for e.g. 20 min of real time.Your Java instance might need to be  powered-up if it hasn't been hit in (I  think) 20 minutes. The benefit is that  they can pass their smart management  on to you as cheaper costs, but it  does mean you'll experience a short  delay, and see a high CPU warning on  the first request in a while.For many cases, Python datastore  access is faster than Java JDO. You'll  likely find that using the low-level  API for Java faster.Some developers seem to have  experienced more datastore errors  thank you would expect (around 0.4-1%  maybe?). I haven't yet.I'm wondering what factors go into determining a PaaS's CPU time (like, in this case, the 6.5 hours free that you get with GAE). For example, does it include the total time it takes for the database to transfer data over to the client?Do the costs under this model increase dramatically as you get more users?
How do cloud platforms-as-a-service measure CPU time?
google app engine;hosting;google cloud datastore;paas
As explained on this page:CPU time is reported in seconds,  which is equivalent to the number of  CPU cycles that can be performed by a  1.2 GHz Intel x86 processor in that amount of time. The actual number of  CPU cycles spent varies greatly  depending on conditions internal to  App Engine, so this number is adjusted  for reporting purposes using this  processor as a reference measurement.In other words, 6.5 hours per day would equal the processing you can get from 6.5 hours of 100% CPU utilization for the mentioned CPU.