[loevborg]

A "hello world" Java program starts up fast, sure. But Clojure start-up time usually takes more than 1 second; it can be 10 seconds plus if you include many jars. I don't know whether that's more the fault of Clojure or the JVM.

[saosebastiao]

It is clojure. Clojure literally bootstraps itself on every startup, and this bootstrap takes a little less than a second even on a fully started jvm. And since none of your clojure code can run until clojure.jar is fully bootstrapped, large clojure projects can easily start up for 5+ seconds before executing a single piece of code.

I love clojure as a language, but my code is usually cli oriented and it was such a terrible fit for it that I switched to Scala. Despite being on the jvm, my startup times are an order of magnitude better.

[jamii]

Fwiw, clojurescript and nodejs starts up pretty fast. The tooling isn't quite as good as clojure yet, but it doesn't take much to out-repl scala.

[adambard]

I have several apps that use Enlive for templating. It's an awesome library, but reading HTML, parsing it out, and producing the templates at compile-time seems to add a very notable chunk to the startup. Better at compile-time than runtime, of course, but definitely something to consider.

[mateuszf]

I don't remember the exact spot, but I think that this video: https://www.youtube.com/watch?v=8NUI07y1SlQ has explanation for why loading clojure programs takes so long.

[exelib]

JVM starts in less than second also for a little bit more as "hello world" java program. But different crappy path/annotations scanning and bytecode manipulating tools like hibernate take a long time.

[nordsieck]

I believe a substantial portion of Clojure's startup time is just reading all of the meta data into memory.