I have this web app that is running ASP .NET MVC 1.0 with LINQ 2 SQL
I’m noticing a very strange problem with LINQ 2 SQL throwing exceptions (mainly Specified cast invalid or Sequence contains more than one element) when under a certain amount of load.
The bigger problem is, I’m not talking about Real Heavy/Professional Stress Testing… Basically what I’m doing is I open FireFox and Chrome and hold down F5 for ten seconds in each (I call this poor man stress testing) – lo and behold; the web app is throwing these exceptions randomly for the next two or five minutes. If I restart the app from IIS7 (or restart WebDev if under Visual Studio) then immediately all is back to normal. Like nothing happened.
At first I was suspecting the way I handle the DataContext, maybe i’m supposed to dispose it at every Application_End from Global.asx, but that didn’t change anything.
Right now I have a single public static DataContext object used by all requests. I’m not disposing it or re-creating it. Is that the right way to do it? Am I supposed to dispose it? When exactly should I dispose it?
There are several things that happen on every request – for example, in every page, the User object (for the current user) is loaded from the database and “LastSeen” attribute is updated to DateTime.Now. Other things (like Tag Cloud for example) are cached.
Any ideas why this is happening?
The DataContext class is not threadsafe – you need to create a new one for each operation. See this article by Rick Strahl (Linq to SQL DataContext Lifetime Management)