probability and web server stress

Ok I have something for all the brainiacs to ponder.

If I stress test my server and find that it can handle X number of simultaneous requests.
I would now know the absolute limit, but it doesn’t take in to account the latency in the web surfing process. Since most of my pages are dynamic I would probably take caching out of the equation. The result I am looking for is the max number of site “viewers” the server can support.

I realize there is probably an equation out there for this. Any suggestions as to where to look?

Now I wish I wouldn’t have slept through math class.

Thanks,

rootdog

That depends largely on how much work each "viewer" is making the server do. For example some viewers will only download large files from your site, whilst some may come to the front page, decide it sucks and leave. Others still will open many pages on your site, browsing through them and then clicking links on them.


Let's say you have x users on your site. Each user will use a certain amount of CPU time during their session. Some users will use it all at once, some users will spread it out over their session. The amount of CPU time varies, for example if they are downloading a large file this requires very little CPU, it is handled by the TCP/IP stack. If they are generating a lot of dynamic pages from various data sources then this will require a lot more CPU time.

In short, you can't really work out how many users your site can cope with, because each user will do different things, which will use your server in different ways varying in their intensity.


Hope this helps.