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At this point I think we are arguing somewhat subjective things. I used to be a hard-core zealot for the JVM as the performance platform of the future - and di

At this point I think we are arguing somewhat subjective things. I used to be a hard-core zealot for the JVM as the performance platform of the future - and did talks arguing just as you are here why HotSpot outperforms $LANGUAGE in real applications. I feel like I'm hearing myself in your argument.. I wrote a signficant portion of the Neo4j storage engine, which is in Java. Now I'm writing another database engine in Rust (sidenote: not for replacing the Neo4j engine, just because it's interesting). Arguably database engines qualify as "significant applications". I find - subjectively: - Maintaining performant code in Rust is easier. I do the same patterns as I did in Java, except it doesn't rely on easy-to-break assumptions of how HotSpot happens to work (ex: stack allocations) - Like you said elsewhere, the issue is often about fragmentation, ultimately stemming from object churn. I find that Rust makes it, culturally perhaps, easier to maintain low allocation code than Java. (sidenote: I think these two points is also why Go code generally has "better GC behavior"; Go doesn't have a better GC, it has a language that encourages less heap allocation) - The engine I'm writing in Rust is faster than anything I've written in Java and - critically - runs for days and months without notable stalls. Come to the dark side!

cogman10 6y ago
I personally like both languages and think they both have a place. My 2 cents. The JVM works exceptionally well when you are dealing with long lived apps which deal with a lot of allocations and the machine running it has a substantial amount of memory. Things like webservers, for example, are near perfect fits for the JVM. Rust does really well when you need high performance, low memory, and ultra fast startup times. It won't necessarily outperform the JVM when you talk about doing a lot of heap allocations (due to heap fragmentation) and it unfortunately suffers from the same heap fragmentation if you are dealing with a long lived server that does a lot of allocations. But then, maybe that performance loss is acceptable for the ability to very quickly scale up and down servers. Now, the JVM is making great strides towards getting faster startup times and even fast performance at startup (AppCDS). However, those strides often involve trade offs with either build complexity or performance losses (such as Graal's AOT). The benefit for rust is that it is as fast as it ever will be without any special build steps or tweaks. Oh, and let's not forget diagnostics. Flight recorder for the JVM is simply AMAZING. The ability to hook up to a poorly behaving production server, start flight recording, and getting detailed information about things like "where are allocations happening" or "what are the hot methods" is simply amazing. No other platform that I know of has the level of detail you can get right out of the box with flight recorder. Certainly not without restarting the application with additional configuration. For example, you'd need a special build of rust with profiling turned on to even start to get the same level of info, doing such also significantly negatively impacts performance.
- pjmlp 6y ago
  Just a small correction, AOT and JIT caches like AppCDS were already available in commercial JVMs like J/Rockit or IBM WebSphere Real Time, as two examples from a couple of possible ones. What is happening now is that the free beer Java users are also getting those features on the package.
pron 6y ago
I'm already on the dark side. Rust isn't my cup of tea, but I do a lot of programming in C++, and hope to one day use Zig for low-level programming. But this does come at a considerable cost, so I do it only when I must -- i.e. I'm targeting a constrained environment or I really need low-level control. The cost isn't so much up front (aside from the big loss in observability), when you first write the code, but low-level languages result in rigid programs that are much harder to evolve over years, certainly with large teams, that with Java. Separate from that, JDK 14 doesn't behave like JDK 8. If you need performance and observability and you are not constrained, then Java is an excellent choice that can have a big positive impact on costs.

cogman10 6y ago

I personally like both languages and think they both have a place. My 2 cents. The JVM works exceptionally well when you are dealing with long lived apps which deal with a lot of allocations and the machine running it has a substantial amount of memory. Things like webservers, for example, are near perfect fits for the JVM. Rust does really well when you need high performance, low memory, and ultra fast startup times. It won't necessarily outperform the JVM when you talk about doing a lot of heap allocations (due to heap fragmentation) and it unfortunately suffers from the same heap fragmentation if you are dealing with a long lived server that does a lot of allocations. But then, maybe that performance loss is acceptable for the ability to very quickly scale up and down servers. Now, the JVM is making great strides towards getting faster startup times and even fast performance at startup (AppCDS). However, those strides often involve trade offs with either build complexity or performance losses (such as Graal's AOT). The benefit for rust is that it is as fast as it ever will be without any special build steps or tweaks. Oh, and let's not forget diagnostics. Flight recorder for the JVM is simply AMAZING. The ability to hook up to a poorly behaving production server, start flight recording, and getting detailed information about things like "where are allocations happening" or "what are the hot methods" is simply amazing. No other platform that I know of has the level of detail you can get right out of the box with flight recorder. Certainly not without restarting the application with additional configuration. For example, you'd need a special build of rust with profiling turned on to even start to get the same level of info, doing such also significantly negatively impacts performance.

pjmlp 6y ago
Just a small correction, AOT and JIT caches like AppCDS were already available in commercial JVMs like J/Rockit or IBM WebSphere Real Time, as two examples from a couple of possible ones. What is happening now is that the free beer Java users are also getting those features on the package.

pron 6y ago

I'm already on the dark side. Rust isn't my cup of tea, but I do a lot of programming in C++, and hope to one day use Zig for low-level programming. But this does come at a considerable cost, so I do it only when I must -- i.e. I'm targeting a constrained environment or I really need low-level control. The cost isn't so much up front (aside from the big loss in observability), when you first write the code, but low-level languages result in rigid programs that are much harder to evolve over years, certainly with large teams, that with Java. Separate from that, JDK 14 doesn't behave like JDK 8. If you need performance and observability and you are not constrained, then Java is an excellent choice that can have a big positive impact on costs.