Have you ever used ngen.exe?

Question

Has anybody here ever used ngen? Where? why? Was there any performance improvement? when and where does it make sense to use it?

Answer 1

Ngen mainly reduces the start-up time of .NET app and application's working set. But it's have some disadvantages (from CLR Via C# of Jeffrey Richter):

No Intellectual Property Protection

NGen'd files can get out of sync

Inferior Load-Time Performance (Rebasing/Binding)

Inferior Execution-Time Performance

Due to all of the issues just listed, you should be very cautious when considering the use of NGen.exe. For server-side applications, NGen.exe makes little or no sense because only the first client request experiences a performance hit; future client requests run at high speed. In addition, for most server applications, only one instance of the code is required, so there is no working set benefit.

For client applications, NGen.exe might make sense to improve startup time or to reduce working set if an assembly is used by multiple applications simultaneously. Even in a case in which an assembly is not used by multiple applications, NGen'ing an assembly could improve working set. Moreover, if NGen.exe is used for all of a client application's assemblies, the CLR will not need to load the JIT compiler at all, reducing working set even further. Of course, if just one assembly isn't NGen'd or if an assembly's NGen'd file can't be used, the JIT compiler will load, and the application's working set increases.