Pre-Jiting a ASP.NET website

Pre-Jiting:-

Managed Assemblies contain Intermediate Language (IL). The CLR JIT-compiles the IL into optimized CPU instructions. The JIT compilation will take a certain amount of time but this startup time can be improved by doing compilation at install time (pre-JITing) using NGEN.exe. This produces a native binary image for the application, thereby eliminating the JIT overhead, but at the expense of portability. When an NGEN-generated image is run in an incompatible environment, the .NET framework automatically reverts to using JIT. Once NGEN is run against an assembly, the resulting native image is placed into the Native Image Cache for use by all other .NET assemblies. A pre-JITed assembly is a persisted form of a JITed MSIL with a class/v-table layout. It is always worth checking performance before and after using this technique as it can actually have an adverse effect.

If a pre-JITed assembly is not installed in the GAC (Global Assembly Cache) , then Fusion (the .NET technology used to locate and load .NET assemblies) needs to verify that the native image and the MSIL assembly have the same version to ensure that the cached native image relates to the current version of the code during binding. In order to do that, the CLR needs to access pages in the MSIL assembly, which can hurt cold startup time.