I have started using JRuby in a Rails project and mostly I am very happy with it. However, one major issue is that Rails startup under JRuby is very slow… and I mean veeery slow. Running a single unit test under JRuby takes 15-16 seconds while running the same test using Ruby (MRI) takes around 0.15 seconds, a factor 100.

The reason for this is that startup of the Rails environment takes a long time under JRuby. When everything is up and running however, performance is great!

So, how to deal with this?

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