ASP.NET debug="false" and line numbers in error stack trace

It's a good practice to always log run-time errors to a database table or a log file or both. It is also nice to have line numbers appear in the stack trace to be able to see where in your code the error appears. For some types of errors, e.g. for exceptions of type NullReferenceException, this is especially relevant as there is no other way to determine what went wrong.

In the past I had to deploy a debug build of the application and set debug="true" within the compilation section of web.config, in order to be able to see the line numbers in error logs. But this is not a good idea, as this adversely affects application performance (see this blog from Scott Guthrie for more details and this blog for even more details). So please, always set debug="false" in production environments. Or, even better, set deployment retail="true" in your production machine.config

But what do we do if we really want more detailed error information in our logs? There appears to be a an easy way to do this. In the properties of your project, in the Build section, select your Release configuration, click Advanced and make sure that Debug Info is set to pdb-only. This is equivalent to setting this compiler option: /debug:pdbonly in the compilerOptions attribute of the compiler element in web.config (for more details about this compiler option read this MSDN article and this blog article). This will emit your optimized release assemblies together with corresponding .pdb files containing all the information needed to reference files and line numbers in exception stack traces. You can then deploy the build output into your production environment.

This will allow you to log error details like line numbers without significantly affecting the performance of your compiler-optimized release assemblies. Warning: if you do this, then also please make sure that you don't set customErrors mode="off" so that you don't expose detailed exceptions to remote users (which is a wise thing to do from security standpoint!)

Happy coding!