Viewstate becomes corrupt under heavy load

gotdablues

I am performing several web stress tests that have the following Test Type settings:

1. 10 Virtual users, For 10 minutes, Steady rate
2. 20 Virtual users, For 10 minutes, Steady rate
3. 40 Virtual users, For 10 minutes, Steady rate
4. 50 Virtual users, For 10 minutes, Steady rate
5. 100 Virtual users, For 10 minutes, Steady rate

As the tests begin to approach 50+ virtual users, the Viewstate becomes corrupt. I begin receiving Http Status Code of
500. In a couple of tests, I received Http Status Code of 503.

I enable various performance counter during the test. For the % Processor Time, the following ranges were found:

10 VU - Avg. 7%
20 VU - Avg. 11%
40 VU - Avg. 16%
50 VU - Avg. 13%

My test environment consists of the following:

.NET 1.1
IIS 6.0 (single application pool)
Windows 2003 Server (standard) SP1, 3.2 Ghz Xeon, 1.0 GB Memory

In addition, I running the ANTS Load tool from the same machine.

Any thoughts?

I can provide result files if it would be helpful.

Thanks.

Brian Donahue

It's hard to comment.

On first impression, I'd say that ANTS Load is doing exactly what it says it'll do and it's telling you the maximum load that the server can handle.

On the other hand, I can definitely say that it's not a good idea to run a large load test from the same server as the web server because you're using because ANTS Load is using resources that would normally be available to the web server. Plus, you're making it more difficult to define exactly what the bottelneck is: it could be the network throughput, but you won't know that if you are making requests to 127.0.0.1.

gotdablues

I made a few modifications to setup.

To correct the ViewState issues, I went through the script and found a case where there was a missing GET. I inserted the WebClient.Get(...) and my ViewState issue seems to have go away.

I moved ANTS off the web server and on to a seperate machine. This made a marginal difference. The big difference was that I switch from 10Mbps to 100Mbps network. The improvements in throughput were expected.

When I run ANTS Load with 100 VU, I am getting an exception. Here it is:

VirtualClient 14 8/19/2005 10:15:55 AM
Exception:
Object reference not set to an instance of an object.
1: Error Description:Object reference not set to an instance of an object.
1: Source:RedGate.Ants.Engine
1: Stack Trace: at RedGate.Ants.Engine.Web.HttpRequest.a(String )
1: at RedGate.Ants.Engine.Web.WebClient.a(String , String )
1: at RedGate.Ants.Engine.Web.WebClient.Get(String url)
1: at RedGate.Ants.NewProject.BrowserClient3.Run()
1: Target Site:Void a(System.String)

Not sure how helpful it is.

Any thoughts on the exception?

Brian Donahue

You had me convinced that the web server itself was breaking down, but aparently you were having an inconsistency in the requests that was causing viewstate errors.

Can you check the BrowserClient3 script and make sure that everything is filled in? For instance all of the GET and POST methods have a URL. Also, I think that you need to have at least one beginpage() and endpage() pair in the script and the URL specified in the beginpage and endpage methods must match and cannot be blank.