100,000 iPhones Overwhelm Activation Server 166
dstates writes "What happens when Apple ships 100,000 iPhone 4S in a day? Answer, 100,000 users all try to activate their new phones. AT&T's activation servers are struggling under the load. Apparently Verizon and Sprint are doing a better job keeping up with the load." Adds an anonymous optimist: "The solution? Call AT&T by dialing 611 and talking to an operator to perform a manual activation with your IMEI and SIM card #, works every time!"
They forgot slowdown curves are hyperbolas (Score:5, Informative)
People assume slowdowns are always linear, so they get the wrong answers, and under-provision all the time (;-))
Assume a really fast activation in 1/10 second, on a machine that's always got 10 CPUs free for the activation jobs. Each CPU will activate 10 phones in 1 second, but if 11 people per CPU request activation, the 11th will wait a full tenth before they start, plus 1/10 second to do the work. The 12th will wait 2/10 plus 1/10 to do the work, and so on.
100,000 people / 10 CPUs = a load of 10,000 users. Plug that into the queuing equation from which I got the above, and the average time to activate will be 999.1 seconds, or 16 minutes. Not fun!
The actual case is probably a lot worse, with slow activations and overloaded servers, but any time when you can get a really large number of users trying to do something in a short period of time, the average time to do the work will be scary large. Unless they just happen to be within the first 10 callers, of course!
That means that you need to temporarily allocate a hugely larger number of resources than you'd expect on first glance. If you and your manager don't already know that the response time curve looks like a hockey stick, you can easily get into a career-limiting situation by under-planning for a predicted overload.
--dave (wearing his capacity planner hat) c-b