Detailed discussion on startup times at http://nicholaskariniemi.github.io/2014/02/11/jvm-slow-start... (and subsequent articles by the same author).

JVM Feature Request: The ability to preserve a complete JVM state (in this case with loaded Clojure stuff) and quickly start from there.

Does anybody know if something like that is possible/already exists?

I have used http://criu.org/ on Ubuntu 14.04 to checkpoint and restore a Java process running a Clojure nREPL server. It took 480 ms to checkpoint a 128MB process and 213 ms to restore on a 2.4ghz E5645.

Not quite what you asked, but I found people recommending this.

https://github.com/ninjudd/drip

> Does anybody know if something like that is possible/already exists?

The majority of commercial JVMs that tend to be ignored on HN, provide JIT cache between runs and AOT compilation.

That's true, but it's generally like this with any Java application. The JVM starts in 0.3 seconds, but loading all your classes usually takes seconds. I don't know the arcitecture well enough, but I think it's because it looks for classes in a lot of places and unpacks JAR files etc.

That of course depends on the number of deps that you have, but you have to have a _lot_ to reach into the second range.

Yep. A JVM doesn't take more than a about 100ms to start up. But Clojure takes a long time, and Leiningen is slow as hell.