This is interesting to me because I am working on a somewhat similar site and a mid-level dedicated server from PowerDNN with 4 gb ram only handling 40 or so users is very scary!!

I'm taking a wild guess here but I would think the main issue is that you are writing to the sql database on every question answer x 40 users - that's a lot of trips to the database in a very short amount of time (71 answers x 40 users = 2,840 trips to database). Whereas if you "held your tongue"  and made only one trip to the database for all 71 answers at the end of the test you would reduce the amount of trips to the database greatly (40 trips to database) AND those trips would be spread out over a greater amount of time.

Don't know what you have built the test in but you could achieve the same "one question at a time" type of UI using either Dynamic Forms or XmodPro. This would also reduce the load on the web server since you would load the entire test on one page - you're just hiding most of the questions from user visibility until it comes time for them to see it.

Just some thoughts and please update this thread as you learn more.

Hi Greg,
Unfortunately there isn't a guaranteed method to 100% predict how many concurrent users a server will handle, however, in most cases, it is a function of both the server and the DNN website itself.  The types of modules used really do have a big impact though - modules like the Text/HTML module perform much better under heavy load than form builder or other highly-dynamic modules.  If you're maxing out your CPU, I would recommend using a program like DotTrace or SQL Server Profiler to find out what DNN component is causing your CPU spike and then work on optimizing/replacing that component.

We have quite a handful of large customers who are getting 1000-1500 concurrent requests per web server (based on Mitch's math, this is 25k-75k "concurrent" users), however, these types of customers generally do a pretty in-depth analysis before adding any new module to their environment.  When you're handling that kind of load, a high-CPU module can mean the difference between needing 20 servers or needing 80 servers.

Even though you're in a single server environment, I would recommend taking a similar approach.  Knowing your environment, you should not expect to achieve the results above, however, by evaluating the modules that you're currently using, you should be able to increase your load.

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Tony Valenti
Tony.Valenti@PowerDNN.com
+001-402-650-6072

PowerDNN.com - World Leader in DotNetNuke Hosting and DNN Hosting
DNN Hosting Australia - DNN Hosting Europe - DNN Hosting US

No clarification needed.  :-)  I know you have my cell number (its 402-650-6072 if anyone else on this thread wants it) and I know you'd be using it if you thought it was a problem with the server.  :-)

Depending on your customer's needs and the duration of the project, if, after Mitch takes a look at it, you still need more horsepower, let me know.  We could look at migrating you to a MiniGrid Cloud or a PowerGrid Cloud depending on your needs.

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Tony Valenti
Tony.Valenti@PowerDNN.com
+001-402-650-6072

PowerDNN.com - World Leader in DotNetNuke Hosting and DNN Hosting
DNN Hosting Australia - DNN Hosting Europe - DNN Hosting US