Always Go to Production in Release Mode
I was at a client's site recently and watched them move the new version of their app to production by copying all the DLLs from the "staging" computer to the production computer. I commented on how that was the beauty of the .NET Framework: Once you had the application installed, upgrades could just consist of replacing the EXEs and DLLs. Of course, I added, you have to remember to do one last compile in Release mode before copying the DLLs.
My client said, "Pardon?" I said, "What!?!"
It turns out that, at my client's site, once a developer got their code working, my client just copied that developer's DLLs to the QA testing site. There's nothing wrong with that ... but my client was leaving money on the table as far as performance goes.
When you press F5 to start debugging, Visual Studio saves and compiles your application. However, that compile is a "fast and sloppy" one -- Visual Studio doesn't do any real optimization of your code. There are a couple of reasons for that. First, this "fast and sloppy" compile gets you into debug mode faster (which is good). Second, skipping optimization avoids rearranging, merging or even eliminating lines of your code, which some compiler optimizations can do. When you're stepping through your source code in debug mode, it's helpful if there's a one-to-one relationship between your source code and your compiled code which rearranging/merging/eliminating makes difficult.
However, when you move to production, you want all of those optimizations. I know that I've said elsewhere that the speed of business applications is controlled by their data access ... but for the cost of going up to the toolbar and changing that Solution Configuration's dropdown list setting from Debug to Release you can, potentially, get a significant improvement in your application's performance (my client estimated about a 10 percent reduction in average response time, for example).
You do have to remember to switch back to Debug mode after doing your "production compile." One of the other things that the Debug mode does is generate a .pdb file that supports debugging (among other things, it provides the relationship between your lines of source code and your compiled code). If you don't keep regenerating that file as you make changes to your source code, your debugging sessions will get decidedly weird.
Posted by Peter Vogel on 09/09/2016