Application's performance deteriorates when running it from Visual Studio

Question

I have an application in C#, which connects to a database and generates some Excel report.

When I run the application inside Visual Studio in Debug mode, this operation takes approx. 101736 milliseconds.

When I open the bin\Debug folder and run the executable from there, that same process (same database, same parameters) takes 33135 milliseconds.

But I'm running the same program.

What can be causing such a huge difference in performance?

I've done this several times, running the application from Visual Studio is always much more slower than running the executable from Windows Explorer.

I'm using Visual Studio 2008 C# Express Edition.

Answer 1

The primary causes of slowdown in the Visual Studio debugger are the following:

1. Large numbers of P/Invoke calls. There are about 100x slower when the P/Invoke MDA is enabled (which is the case when the debugger is attached, even if no breakpoints are set). The overhead is a fixed amount for every P/Invoke method invocation, so if a single P/Invoke execution is slow then you won't notice a difference, but if your method is doing something like return a+b; and called hundreds of thousands of times, you'll get hit hard.
2. Tracepoints and/or conditional breakpoints. These are only slow when they are actually getting hit. Tracepoints are hard to "hide" since you can see their output, but I've seen cases where conditional breakpoints were executed millions of times leading to very slow execution in the debugger.
   • Note: regular (unconditional) breakpoints are extremely fast, with little to no overhead in the debugger.
3. IntelliTrace call tracing mode enabled (applies to Visual Studio 2010 and newer, Ultimate Edition). IntelliTrace has two settings: events mode is fast but call tracing mode can pose a significant overhead.
4. Large numbers of exceptions getting thrown. If your application is throwing many thousands of exceptions, then you may see a slowdown in the debugger.
5. Trace and/or Debug output. If your application is calling Debug.WriteLine or Trace.WriteLine many (read: thousands of) times, it could slow your application down while attached to the debugger.