4 ms·

So if I care about performance, I would use the JVM? I spent years as a performance engineer on HFT trading systems tuning JVMs. It’s possible to get very good

by nvarsj 6y ago

So if I care about performance, I would use the JVM? I spent years as a performance engineer on HFT trading systems tuning JVMs. It’s possible to get very good performance on the JVM, but it is also hard and for the layman almost impossible. Yes, it has great throughput, but only because it has to. The design of hotspot / JVM and the languages that run on it encourages massive heap allocations of gigabytes a second. I can’t think of any other language or runtime that is comparable in terms of its memory bloat. Even if you control allocations, and have happy path GCs, hotspot GC still causes occasional pauses of 10-100s milliseconds. And this is considered good. I know that lots of people have built careers on the JVM and defend it vigorously. Whenever I make a comment that is negative on the JVM, I always get downvoted without fail on HN. I used to be one of these people, after all, so I can relate. If I truly cared about performance these days, I’d use C++ or Rust. Otherwise, I’d use a language like golang with reasonable default GC behavior and allocation patterns - where I know the daemon I write won’t use more than 100-200Mb, and probably even less, and will typically have sub-ms pauses. I think even most scripting languages, like Ruby/Python, have reasonable memory usage and GC patterns for web development, but I’m not as familiar with them. I probably care more about energy consumption these days though. And again, the JVM is the worst offender. The average developer building a Java web app will create something which consumes gigabytes of memory usually. These apps tend to spend the majority of their CPU time allocating and GCing memory. I can only guess how much server time has been consumed to satiate the memory hungry needs of the JVM.

pron 6y ago
> So if I care about performance, I would use the JVM? No. If you use the JVM you might well care about performance. If you care about performance, you should consider the JVM. > I spent years as a performance engineer on HFT trading systems tuning JVMs. The JVM is not designed to give you 100% performance (of the ideal offered by the hardware). It's designed to give you the easiest means of achieving ~95%, provided you're OK with some nondeterminism. > I’d use a language like golang with reasonable default GC behavior and allocation patterns - where I know the daemon I write won’t use more than 100-200Mb, and probably even less, and will typically have sub-ms pauses. You'd be wrong, because JDK 14 will most likely give you substantially better performance than Go out of the box; JDK 15 and 16 even more so. BTW, the footprint and performance profile of JDK 14 is worlds apart from JDK 8. The JVM has been undergoing some very big changes in the last couple of years. > And again, the JVM is the worst offender Nope. https://greenlab.di.uminho.pt/wp-content/uploads/2017/09/paperSLE.pdf https://greenlab.di.uminho.pt/wp-content/uploads/2017/09/pap...
- nvarsj 6y ago
  Thanks for the paper. The data tables for it just proves my point. For example, in the binary-trees test, Java used 1120 Mb. Go used 228, Rust used 180, Lisp used 373, Haskell used 494 Mb. Only Jruby and Erlang seem to require more memory usage. If a webapp performs similar to this experiment, I could rewrite it in almost any other language and I’d cut the required number of servers in half or more.
  - pron 6y ago
    Java absolutely requires more memory; less so in 14, but still. That does not, however, make your point about either performance or energy, both of which are wrong. > If a webapp performs similar to this experiment, I could rewrite it in almost any other language and I’d cut the required number of servers in half or more. Nope. Because you gain in performance where you lose on memory. If you add more RAM, you'd pay for less hardware and consume less energy. Anyway, if you last experienced Java in version 8, try 14. It's not what you might remember. You'd likely see a 10-40% reduction in cost-per-transaction, plus very low pauses with the new GCs. OpenJDK's VM in 14 is just significantly different from what it was in 8.
    - merb 6y ago
      well no matter what you are trying to say, but without valhalla and other techniques to reduce allocations java will always be slower than the languages the other poster said. no matter how good a gc gets, if it does need to do double the work of another gc it is not a problem of the gc. it is that too much allocation is needed even for simple things. java tried to tune their gc over and over instead of just fixing the problem. allocations.
      - pron 6y ago
        > java will always be slower than the languages the other poster said That's true, and while Valhalla will help close the gap, it is important to understand that Java's goal is not to be the fastest language, but to be the language where it's easiest to get to 95% of full performance potential. I don't think any other language achieves that as well as Java. The question, then is how much you're willing to pay for that extra 5%. In other words, for every Java program X, there exists a C/C++ program Y that's at least as fast. But is the cost of writing Y worth it given the particular performance benefit? The reason Java is so popular is that the answer is very, very often no. And remember that the lower Java costs are not just in the "coding costs" of writing and maintaining, but also in observability. These days, thanks to the Java Flight Recorder, Java gives you unparalleled insight into what your application is doing for very little overhead.

by nvarsj 6y ago

pron 6y ago

> So if I care about performance, I would use the JVM? No. If you use the JVM you might well care about performance. If you care about performance, you should consider the JVM. > I spent years as a performance engineer on HFT trading systems tuning JVMs. The JVM is not designed to give you 100% performance (of the ideal offered by the hardware). It's designed to give you the easiest means of achieving ~95%, provided you're OK with some nondeterminism. > I’d use a language like golang with reasonable default GC behavior and allocation patterns - where I know the daemon I write won’t use more than 100-200Mb, and probably even less, and will typically have sub-ms pauses. You'd be wrong, because JDK 14 will most likely give you substantially better performance than Go out of the box; JDK 15 and 16 even more so. BTW, the footprint and performance profile of JDK 14 is worlds apart from JDK 8. The JVM has been undergoing some very big changes in the last couple of years. > And again, the JVM is the worst offender Nope. https://greenlab.di.uminho.pt/wp-content/uploads/2017/09/paperSLE.pdf https://greenlab.di.uminho.pt/wp-content/uploads/2017/09/pap...

nvarsj 6y ago
Thanks for the paper. The data tables for it just proves my point. For example, in the binary-trees test, Java used 1120 Mb. Go used 228, Rust used 180, Lisp used 373, Haskell used 494 Mb. Only Jruby and Erlang seem to require more memory usage. If a webapp performs similar to this experiment, I could rewrite it in almost any other language and I’d cut the required number of servers in half or more.
- pron 6y ago
  Java absolutely requires more memory; less so in 14, but still. That does not, however, make your point about either performance or energy, both of which are wrong. > If a webapp performs similar to this experiment, I could rewrite it in almost any other language and I’d cut the required number of servers in half or more. Nope. Because you gain in performance where you lose on memory. If you add more RAM, you'd pay for less hardware and consume less energy. Anyway, if you last experienced Java in version 8, try 14. It's not what you might remember. You'd likely see a 10-40% reduction in cost-per-transaction, plus very low pauses with the new GCs. OpenJDK's VM in 14 is just significantly different from what it was in 8.
  - merb 6y ago
    well no matter what you are trying to say, but without valhalla and other techniques to reduce allocations java will always be slower than the languages the other poster said. no matter how good a gc gets, if it does need to do double the work of another gc it is not a problem of the gc. it is that too much allocation is needed even for simple things. java tried to tune their gc over and over instead of just fixing the problem. allocations.
    - pron 6y ago
      > java will always be slower than the languages the other poster said That's true, and while Valhalla will help close the gap, it is important to understand that Java's goal is not to be the fastest language, but to be the language where it's easiest to get to 95% of full performance potential. I don't think any other language achieves that as well as Java. The question, then is how much you're willing to pay for that extra 5%. In other words, for every Java program X, there exists a C/C++ program Y that's at least as fast. But is the cost of writing Y worth it given the particular performance benefit? The reason Java is so popular is that the answer is very, very often no. And remember that the lower Java costs are not just in the "coding costs" of writing and maintaining, but also in observability. These days, thanks to the Java Flight Recorder, Java gives you unparalleled insight into what your application is doing for very little overhead.