Question

Is there a proper way, equation or technique in general to say, “My web application needs to support N number of total users which via this equation/technique/rockHardExperience tells me that I need to support X number of concurrent page requests”?

From my research and/or gut feeling it seems like it would be something like:

totalLoadCapabilityRequired = (totalUsersN x .10 ) * .5

where .10 is for roughly 10% on at any given time

and the whole thing multiplied by 50% to suggest a 50% chance of those total users online executing a request at roughly the same time

any insights would help me in making sure I implement support in my application that is on par for the demand. I expect a lot of users but don’t want to over anticipate too early. I know for starters that the org I am programming for will have 45,000 users that they want to use my system, with an anticipation on success for many more.

Answer 1

Here’s a couple of things to think about:

1. What’s the time span in which you expect the bulk of your visits? If it’s an office application within the same physical company your capacity planning should be based on an 8 hour period. If most visits will come from the same continent you can plan for a 12 hour period instead, etc. Base your visitor spread on that.

2. Which pages do you anticipate will be the most popular and how heavy are those pages (i.e. how many pages can you load in one second)? Get an understanding of parts that would benefit from caching to squeeze out more performance.

3. Don’t plan based on peak load; design your app to scale and start small.

4. Design your app in a way that you can take run snapshots at every 500th request; you can use tools like xhprof to create files that you can run through cachegrind tools to analyze the performance as it runs.

In short, there’s no catch-all formula 🙂 for a ballpark figure your formula will probably be good enough, but take the above points in consideration.