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How Fast Does Java Compile? (mill-build.org)
44 points by jatcwang 2 hours ago | hide | past | web | 22 comments | favorite





We slow our build down by having a dozen 'tools'-projects with a handful of classes each in a straight dependency-line above our main project that contains 99% of the code. This easily increases our compile time from a few seconds to several minutes. With a bonus chance to cause an infinite IDE workspace build loop.

That's a nice writeup. Given the hot/cold difference you observe, I'd be very curious to see how builds compare when using maven daemon or gradle daemon.

I am not very familiar with those myself, simply aware of them.

[1] https://github.com/apache/maven-mvnd

[2] https://docs.gradle.org/current/userguide/gradle_daemon.html


The benchmarks in the article do use the Gradle daemon, but not the Maven one, mostly because mvnd isn't the default.

For Gradle, if you turn off the gradle daemon, it gets even slower than the numbers presented going from 4+ seconds to 10+ seconds per compile:

    lihaoyi mockito$ git diff
    diff --git a/gradle.properties b/gradle.properties
    index 377b887db..3336085e7 100644
    --- a/gradle.properties
    +++ b/gradle.properties
    @@ -1,4 +1,4 @@
    -org.gradle.daemon=true
    +org.gradle.daemon=false
     org.gradle.parallel=true
     org.gradle.caching=true
     org.gradle.jvmargs=-Xmx2048m -Dfile.encoding=UTF-8 \

    lihaoyi mockito$ ./gradlew clean; time ./gradlew :classes --no-build-cache
    10.446
    10.230
    10.268

Oh wow. That's... something. :)

Author here, hope people find this article interesting!

"From this study we can see the paradox: the Java compiler is blazing fast, while Java build tools are dreadfully slow."

Hi, nice article! I wholeheartedly agree with the conclusion after 10 years of fighting with maven for performance gains (that I always measured in minutes not seconds).

Slow feedback cycle is the root of all evil.


I thought java was tokenized, not compiled. That's why you need their runtime environment isn't it?

It is compiled to Java byte code. The JVM runs the byte code.

Tokenization [1] is the process of splitting text into components called tokens. It's usually the first stage of parsing.

[1]: https://en.wikipedia.org/wiki/Lexical_analysis#Tokenization


We used to have Java CPUs

https://en.m.wikipedia.org/wiki/Java_processor

The JVM is just to run the code on other systems, and is the most common way of running compiled Java code.


Java is compiled down to bytecode and there is a bunch that happens in the compiler to make things fast ahead of the JIT.

I think it means "compile it into bytecode", which can then be run by the Runtime.

So like most JIT languages nowadays?

How fast does Golang compile? https://www.octobench.com/

Huh, so for anyone interested but did not have the time to do the comparison of the two links of OP and parent post:

* java (on a cold jvm): 18.000-32.000 line per second on a single core

* java (on a hot jvm): 102.000-115.000 line per second on a single core

* golang: 28.000 line per second on 12 core


What I love most is how people project.

I was just saying "How fast does Golang compile" because I'm interested in compilation speeds and CPU usage cross compilers.

I've been using Java from 1996 on for two decades.


Pretty impressive numbers, although it’s fair to say here that while Go comes with its own build toolset, pretty much no one uses plain javac to compile stuff. It’s almost always either Gradle or Maven and as the article hints they slow down builds a lot.

> From this study we can see the paradox: the Java compiler is blazing fast, while Java build tools are dreadfully slow. Something that should compile in a fraction of a second using a warm javac takes several seconds (15-16x longer) to compile using Maven or Gradle.

edit: typos


I'd be curious to see what the slowdown is, because my gut feeling is that it simply comes down to QoL stuff tools like maven do. If we keep it to compiling only, stuff like resolving dependencies from the pom.xml and such.

Yes but reality is even worst maven projects take f*"* eternity like the post says, you have tens of atomyse package that make simple task that should take seconds take minutes, while the fast in go is not only the compilation time, but that 28000 is in real word case,at least it'd feels like this for experience.

How fast does Rust compi..... I better not actually.

Why? I'm quite curious. There aren't any good benchmarks on the internet, especially ones comparing it to other languages. I'd love to actually see some real numbers showing how far off it is from Java or Go (I don't doubt it is slower than Java or Go, as it is a much more sophisticated language).

My anecdotal evidence suggests it is not as slow as many think. It compiles a 500k LoC (that's count of all code in dependencies) project in ~10s on my M2 Pro.


Subjectively, not baked by any science, the Linking step is the worst, even with mold.

Don't worry, I wrote this article about Java but my day-to-day work is Scala. We're lucky if we can crack 4,000 lines-per-second-per-core on my pretty vanilla Scala projects x_x

About my only gripe with the language.

But it's getting better.




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