One of the main culprits when it comes to ASP.NET concurrency is caused by the fact that default sesion state has been implemented using a pessimistic locking pattern. Basically, any standard handler, whether that be an ASPX page, a generic handler or an ASMX web service, goes through the following steps:
When your w3wp process is stuck at 100% like, like when I used a non-thread-safe Dictionary concurrently, you may want to identify what request the runaway thread is actually serving. Let me show you how to identify which request caused a runaway thread, using windbg.
Having analyzed the process dump in part 1, let’s take a look at the code we suspect of causing the issue, in particular how race condition bugs can be avoided.
This is the story of how a simple oversight resulted in a tough to catch bug. As is often the case, it worked on my machine and only manifested itself in production on a live site. In this series we will look at analyzing 100% CPU usage using Windbg.
In this post I’ll walk you through how to setup IIS Application Request Routing so that any requests for a /wiki/ subdirectory are routed onto a separate server, while all other requests are handled by the server itself.
What does Flash, upload, cookies, IIS load balancing and cookies have to do with each others? More than I’d like :(
One of my earlier blog posts, and the all time most popular one, was about how to make URL rewriting on IIS 7 work like IIS 6. While my method did provide a means to the goal, it’s humiliatingly far from what I should’ve done. Since the old post is still the most visited post on my blog I feel obligated to write a followup on how to do proper url rewriting in IIS 7.
A single server has started to sometime leave zombie w3wp.exe processes when trying to recycle. A new process is spawned properly and everything seems to work, except the old processes are still present and take up memory. Task manager reports there’s only a single thread left, far from the active ones that have between 40 and 70 threads usually. Using ProcDump I’ve taken a full memory dump to analyze further in WinDbg. The machine is a Server 2008 R2 x64 8 core machine as stated by WinDbg:
I recently put a number of load balanced websites in production by using the newly released IIS7 Application Request Routing v2 Beta extension. Everything seemed to run perfectly both performance and functionality wise. There was a slight problem however.
Once you start distributing your ASP.NET website across multiple webservers, you’re going to need a way to share session state. That is, unless your app is stateless, in which case scaling it should be a breeze!
When adding sites to IIS7 either by script or by editing the config files directly, you may receive an error in the sites list that says:
Some time ago Peter Loft Jensen wrote about how to easily give a user account the neccessary permissions to access the IIS metabase & required directories, and thus be used for running the IIS process.
Upgrading to IIS 7 should be rather transparent, unfortunately that is not the case when it comes to URL rewriting as we knew it from IIS 6. In IIS 6 all we had to do was to add a wildcard mapping making sure that all requests went through the ASPNET ISAPI process. After this was done, one could create a global.asax file that would either pass requests directly through or rewrite the URL based on an internal algorithm.