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Improve the startup performance of your .NET apps

In our continuous quest to improve the performance of our applications, I found the following ‘trick’ to improve the startup times of your application:

Add large assemblies to the NGen cache on the server

While profiling our ASP.NET applications, we noticed that some of them took a long time(>15 seconds) to render their first page after a cold start. The problem is that some of the assemblies used inside our application (I’m looking at you Entity Framework!) are quite large. Every time the application restarts, these large assemblies needs to JIT-ted.

To avoid the JIT cost, we can create a native image using ngen. The runtime can use these native images from the cache instead of using the just-in-time (JIT) compiler to compile the original assembly.

Let’s go through the steps:

  • Login on the server
  • Open an Administrator command prompt
  • Browse to the bin folder of one of the (slow) apps
  • Execute the following command for every DLL you want to add to the NGen cache:
    • "C:\Windows\Microsoft.NET\Framework64\v4.0.30319\ngen.exe" install <dllname>.dll

You only need to do this for one applications as all apps will share the cached native image.

Note: don’t forget to measure before and after. It doesn’t make sense to do this for all assemblies.

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