[pseudoramble]

I’ve been out of the Java scene for a really long time, but will be coming back to it soon. I’m curious - these performance issues described here, are they inherit to how Java itself? Is it baggage from Spring/Boot? Are there ways to get more bang for the buck with some careful choices in a system like this?

The closest I’ve done to Java recently is C#, which I think may have similar challenges, but overall didn’t seem quite as bad if you avoided lots of framework extras. It also wasn’t something I was digging into deeply though, so perhaps I’m mistaken.

[voidfunc]

You can write clean beautiful Java and make it perform beautifully if you're careful with what you pull in for dependencies... but then you're not really using Java to its full potential as an ecosystem for basically building massive line of business apps and services that you can spin up everything from junior to offshore to 30 years of experience developers. The tradeoff for this is performance and it's a thing a lot of companies are willing to trade off on.

Things get messy the moment you involve large frameworks, reflection, ten different approaches to parallelism etc. There's also the problem of code base evolution in Java. Code before JDK-8 feels different than code after it and there's a lot of Pre-JDK 8 code out there in the wild.

And that's just it at the end of the day... it's a cultural difference in the ecosystems.

[gred]

My experience with very simple Jersey web apps is ~1.5 seconds to start up. Much less than his reported ~8 seconds with Spring Boot, but still not in the 100 ms range he reports with Go. I assume one second or so is about as low as you can go with a mainstream Java framework without AOT, though I'd be happy to be corrected.

[maccard]

I worked on an app in kotlin a while back, and am currently working in a dotnet app. We can run our entire unit test suite faster than the JVM started up on that project.

Also, 8 seconds is quick in my experience for Java - I’ve seen more like 15-30

[p2detar]

Can confirm with Vert.x. I used to have a JRebel subscription for code hot swapping in another project but in my current Vert.x thing I simply don’t need it. It’s just fast.

[matsemann]

Also, you don't have to continuously restart the server for every change. Can hot swap code. And for tests there are solutions to keep the jvm running between the code->test->fix cycle. But I've never felt the need for those, running a single test is often plenty fast as one doesn't need to instantiate the whole app, only the dependencies needed for the test. So plenty fast.

[xxs]

Spring by far - Spring is effectively a build tool running at run time (scanning, enhance, code generation, etc.) - most of it is just startup as JVM does a decent job at optimizing the cruft. In most cases the boot times don't matter, though - at least for most people, esp. when it comes to production. (it's mostly developers time wasted)

I have some personal experience optimizing Spring to record previous runs and effectively cache resolution and code generation, etc. for massive boot latency improvements. Never got around contributing it back, though (not a real spring user)

[jamesfinlayson]

> most of it is just startup

Yep, I have some Spring code in AWS ECS and it hits 100% CPU usage on start-up before dropping back to 1.5% when idling (this is with 1 vCPU I think).

But yeah I remember reading one of the Spring devs say that some (a lot?) of the runtime reflection could be done at compile time but isn't.

[jeroenhd]

In my experience, if you write Java like you'd write to, you'd probably get similar performance. Maybe AOT performs a bit better, maybe it doesn't because it disables live optimizations.

Java doesn't lend itself well to writing Go style code, though. You quickly end up writing very "Java" Java code. That has some advantages (code deduplication, less boilerplate) but also downsides (allocation overhead, performance impacts).

In terms of Java vs C#, I don't think you'll notice too many new issues. If you opt into using heavy frameworks like Spring Boot to solve annoying problems for you, you'll see RAM usage increase massively, but it'll also take care of a lot of annoying grunt work for you. Startup times overall are pretty similar. The biggest downside in my experience is the lack of nullable types (@Nullable annotations are a poor substitute) and some syntax improvements that are new to Java but have been part of stable C# for many years.

As long as you stick with small libraries and avoid writing too much ObjectInjectorFactoryProducerResolver style code, performance of the JVM is fine.

All of that goes as long as you're able to use modern toolkits. If you're stuck in the world of Enterprise Java with Oracle Java 8, you'll notice old Java's shortcomings a lot more.

[nelup20]

You can do AOT compilation with GraalVM to reduce both startup times and memory usage, but then you don't have the JIT.

[e44858]

I think this upcoming feature will let you have both AOT + JIT without needing GraalVM: https://wiki.openjdk.org/display/crac

[tomohawk]

Having done a lot of Java and Go, Go has much better mechanical sympathy between the language, libraries, and vm than Java does. The JIT GC in Java are marvels of engineering, but they have to be.

As an example, in Java, everything is a pointer, so pointer chasing all the time, which is not good for cpu cache, etc. In Go, there is first class support for composition.

The other main adjustment, if coming from Java, is reduced cognitive overhead. It usually only takes a week or two for an experienced Java dev to be reasonably effective in Go, but it takes a few months to break the mental habits of overthinking everything.

[re-thc]

> As an example, in Java, everything is a pointer, so pointer chasing all the time, which is not good for cpu cache, etc

Strictly speaking that's not true. It's everything is a pointer in theory to make it easier to reason with and JIT / JVM optimizing in the background.

There are primitive types and there are lots of tricks in the JVM e.g. escape analysis that places objects on the heap/stack etc.

[codr7]

There's nothing forcing you to write EE style code in Java though, or depend on frameworks written in that style.