Hacker News Reader

Comment by tormeh | Hacker News Reader

I don't really understand all the complaining about JVM startup times. It's a second; usually less. Unless you're using JVM apps as command line utilities I don't see the problem.

View on HN

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.

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.

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.

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.

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.

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.

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

I think the mention of JVM start up time is a bit erroneous. A mechanism for uninterrupted service during deployments is needed whether the JVM takes a millisecond, a second or a minute to load up.

The article is interesting though.

But the site is still down for some period of time, even if it's less than a second. That's unacceptable for applications with many users that are deployed many times per day.

Reply on news.ycombinator.com