A subject close to my heart, I write a lot of heavily optimised code including a lot of hot data pipelines in Java.

And aside from algorithms, it usually comes down to avoiding memory allocations.

I have my go-to zero-alloc grpc and parquet and json and time libs etc and they make everything fast.

It’s mostly how idiomatic Java uses objects for everything that makes it slow overall.

But eventually after making a JVM app that keeps data in something like data frames etc and feels a long way from J2EE beans you can finally bump up against the limits that only c/c++/rust/etc can get you past.

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polothesecond 6 hours ago | parent | next [-]

> And aside from algorithms, it usually comes down to avoiding memory allocations.

I’ve heard about HFT people using Java for workloads where micro optimization is needed.

To be frank, I just never understood it. From what I’ve seen heard/you have to write the code in such a way that makes it look clumsy and incompatible with pretty much any third party dependencies out there.

And at that point, why are you even using Java? Surely you could use C, C++, or any variety of popular or unpopular languages that would be more fitting and ergonomic (sorry but as a language Java just feels inferior to C# even). The biggest swelling point of Java is the ecosystem, and you can’t even really use that.

	▲	yunnpp 2 hours ago \| parent [-]
		I am very interested about this and would like an authoritative answer on this. I even went as far as buying some books on code optimization in the context of HFT and I was not impressed. Not a single snippet of assembly; how are you optimizing anything if you don't look at what the compiler produces? But on Java specifically: every Java object still has a 24-byte overhead. How doesn't that thrash your cache? The advice on avoiding allocations in Java also results in terrible code. For example, in math libraries, you'll often see void Add(Vector3 a, Vector3 b, Vector3 our) as opposed to the more natural Vector3 Add(Vector3 a, Vector3 b). There you go, function composition goes out the window and the resulting code is garbage to read and write. Not even C is that bad; the compiler will optimize the temporaries away. So you end up with Java that is worse than a low-level imperative language. And, as far as I know, the best GC for Java still incurs no less than 1ms pauses? I think the stock ones are as bad as 10ms. How anyone does low-latency anything in Java then boggles my mind.

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dikaflowt 5 hours ago | parent | prev [-]

Can you share the libs you 're using?