Question

Consider a web application that resizes large tiff files on the fly. Each large tiff file is resized into a jpg thumbnail and larger jpg when the user invokes the operation. The dimensions of these converted files is always the same.

During a code review yesterday, one of the other developers asked me why I set those dimensions in my global.asax like so:

    Application["resizedImageWidth"] = int.Parse(ConfigurationManager.AppSettings["ResizedImageWidth"]);

, instead of just looking up the value via a Configuration file during the actual method invocation. I store the widths in the configuration file in the event the end user’s after testing the application would like to alter dimensions so I would not have to change code inline.

The reasoning I gave was to prevent the read from the configuration file each time an image was generated, but could not answer if there was similar overhead during a lookup to application level variables. This optimization probably doesn’t affect performance to a large scale, but I wanted to know what the community thought the more efficient solution was, i.e. set them during Application start up, or read them on the fly during method invocation.

Answer 1

Generally you should read from the configuration on the fly as you need it. The framework will cache the configuration file, so it is fairly performant. And I believe (Don’t quote me) that ASP.Net can monitor and bring in the changes to a configuration file without restarting the application.

I typically like to create a Configuration class which will hide the details of where the value is stored:

public static class Config
{

   public static int GetXDimension()
   {
      ...
   }

}

This keeps your calling code clean from the configuration code, and if you find I’m wrong, you won’t have to change your code everywhere.