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We've been using Rust in production for Skylight (https://www.skylight.io) for many months now, and we've been very happy with it.

Being one of the first to deploy a new programming language into production is scary, and keeping up with the rapid changes was painful at times, but I'm extremely impressed with the Rust team's dedication to simplifying the language. It's much easier to pick up today than it was 6 months ago.

The biggest win for us is how low-resource the compiled binaries are.

Skylight relies on running an agent that collects performance information from our customers' Rails apps (à la New Relic, if you're more familiar with that). Previously, we wrote the agent in Ruby, because it was interacting with Ruby code and we were familiar with the language.

However, Ruby's memory and CPU performance are not great, especially in long-running processes like ours.

What's awesome about Rust is that it combines low-level performance with high-level memory safety. We end up being able to do many more stack allocations, with less memory fragmentation and more predictable performance, while never having to worry about segfaults.

Put succinctly, we get the memory safety of a GCed language with the performance of a low-level language like C. Given that we need to run inside other people's processes, the combination of these guarantees is extremely powerful.

Because Rust is so low-level, and makes guarantees about how memory is laid out (unlike e.g. Go), we can build Rust code that interacts with Ruby using the Ruby C API.

I'm excited to see Rust continue to improve. Its combination of high-level expressiveness with low-level control is unique, and for many use cases where you'd previously use C or C++, I think Rust is a compelling alternative.




Somewhat OT, but...

I'm looking at your pricing, and I don't have any idea how you define the notion of a "request". Right now, I can't even begin to guess what pricing bucket my apps might fit into, and that reduces my motivation to try out your service. I speculate I'm not the only person who's felt this way.

(also, I know why you include the Ember mention at the bottom, but I really don't care. I'd rather see your awesome UI than hear what technology it's based on.)

Edit: Seriously, I'm getting downvoted for offering someone feedback on their product experience?


Don't let it get to you - upvote and downvote are very close for mobile users. Here you have a +1 to compensate. :)


Love that you guys are using Rust in production. Very elegant design (AS::Notification IPC -> Rust).

I'd dump the part of the marketing site talking about the fast UI on Ember. It's cool that you guys use Ember and you're proud of it, but I want to see more about your product. Show me how easy it is to drop into an app, or reports you generate, alerts you flag, etc..

Ultimately, while I nerd out on what a product is built with, I only care about what it can offer me. Fast UI isn't a feature, it's an expectation.


"We end up being able to do many more stack allocations, with less memory fragmentation and more predictable performance, while never having to worry about segfaults."

But isn't this stuff the job of the VM? There's no reason why a program written in Ruby can't do the same stack allocations, reduced memory fragmentation and predictable performance automatically - if the Ruby VM was better designed.

If Ruby had a better VM would you chose to use it over Rust? In Rust are you doing things that the VM could be doing for you?


> There's no reason why a program written in Ruby can't do the same stack allocations, reduced memory fragmentation and predictable performance automatically - if the Ruby VM was better designed.

Escape analysis falls down pretty regularly. No escape analysis I know of can dynamically infer the kinds of properties that Rust lets you state to the compiler (for example, returning structures on the heap that point to structures on the stack in an interprocedural fashion).

This is not in any way meant to imply that garbage collection or escape analysis are bad, only that they have limitations.


Rust must statically prove lifetime of references to stack allocated variables does not exceed lifetime of the variables they point to at compile time, in order to be 100% memory safe. How is that different than just an advanced escape anlysis? Theoretically a VM could do much more, because it could do speculative escape analysis (I heard Azul guys were working on such experimental thing called escape detection) and even move variables from stack to heap once it turns out they do escape.


You could do escape analysis equivalent to Rust's only if you inlined all the functions. Sometimes, that's simply not possible, e.g. with separate compilation.

On the other hand, Rust is still able to perform its kind of escape analysis (via lifetime-tracking type system), because the relevant facts are embedded in type signatures of Rust functions, and as such must be present even for separate compilation (even if the actual implementation of the function is unknown).


VM could do see all the functions and do whole-program analysis. Inlining is an orthogonal concept.


You could in theory, but that analysis would likely be really slow.

In any case, without the type system and compiler to enforce the discipline the programmer is going to lose a lot of control and predictability.


Not necessarily. As you said, Rust encodes that information in type signatures. Exactly the same information can be used in a VM and it could do escape analysis one method at a time then.


That's true. Maybe it would work, but I wonder if anyone has attempted it before...


For one thing, Rust can reject programs at compile time if it's not satisfied with its analysis. For Ruby to get that, you might have to restrict the language in a similar way.


The JVM, who is several order of magnitudes better than the Ruby VM, constantly gets smashed in terms of performance and memory usage by a well designed C++ program.

Why? Because in theory, a VM should be able to do as well, if not better, than a programer.

The limit of a VM is that you are extremely limited in the amount of resources you can allocate to the VM to determine how much resources should be freed. See what I mean?

In the end the VM is nothing less than a program. With RAII, for example, there is zero overhead associated with the decision of releasing a memory block, because it's compiled into the program.

On top of that if you start to add some nasty memory optimization tricks allow you, you start to get why manually managing memory is still very interesting when performance and/or memory usage is important.


Both the JVM and the CLR are regularly beaten by C/C++, despite claims that they are "as fast". What gives?

In my view the whole problem comes down to whether or not you are using an idiomatic approach or not. In idiomatic C#/Java you use a lot of heap allocations, garbage collection, you may be using dynamic dispatch and so on.

If you write a C# program that uses stack allocation only (no classes, only structs and primitives), no inheritance/polymorphism, no exceptions, you should find that the CLR stands up pretty well to a C++ program. Sadly, what you have done then is essentially code in a very small subset of C#, OR you have achieved something that is so hard and so prone to foot-shooting you could just as well have used C++ to begin with.

To reverse the argument: if you use C++ with loads of garbage collected objects etc. you will end up with performance similar to a java/C# program. But in idiomatic C++, you usually don't.


C# lacks the language features to make dealing with such coding style sane and the libraries use the "idiomatic" approach - if you're willing to put on a straitjacket and throw away the libraries then why bother with C# ?

That's not saying that C# can't be made more efficient by avoiding allocation in performance critical sections, but overall it's going to perform worse than C++, both idiomatic and non idiomatic versions. It's just that for most use cases C# is used the performance difference isn't relevant anyway.

Java doesn't even have value types, so it can't even come close in terms of memory layout efficiency and avoiding allocations without perverse levels of manual data structure expansions - for eg. consider how would you do the equivalent of : struct small { int foo; float bar; char baz; }, std::vector<small>.


I agree completely. For an "inner loop" scenario in C# you have to use the straight jacket version of C#. Luckily you can use idiomatic C# for the rest of the program.

The option to using "straight jacket C#" is using C/C++ interop for a part of the program. If that part is large enough, such as in most high end games, it's usually worth biting the bullet and go C++ throughout. Luckily again, those programs are rare.

Point is still that C-style C# is almost as fast as C++ (modulo compiler specific optimizations) but for the reasons above, that fact isn't very interesting.


Java will have value types soon. Also, C++ does some heap allocations behind-the-scenes quite often (e.g. with vector or string) which are hard to get rid of and they are much more expensive than in JVM/CLR. So not always idiomatic C++ smashes JVM/CLR in performance. YMMV and typical differences are small enough to not matter for most of server-side software like web-apps, web-servers or databases.


> What gives?

What gives is this. The people who right these fast C/C++ programs that beat Java/C# are usally far more skilled and trained.

Any programmer who know neither language well and has to write a big application in it will probebly find java/c# far easier.

I remember a long blogpost where somebody set out to test this on himself. And that guy was a very good C++ programmer. He found that his C++ prgrogrammer was slower, but he then set on improving the speed and in the end beat java by quite a bit. However the amount of effort was completly unreasonable for most programmers.

So "What gives" is this, and this has been true for a long time. If you are a expert in a low level language and spend time optimizing you will probebly beat Java/C#.

I would suggest that you should look into what a JIT or GC can and can not do. Some of the performance problems you identivy are really almost never a bottleneck anymore.


(I think shin_lao was actually talking along the same lines, saying that even the hyper-optimised JVM often isn't as good as a good C++ program.)


I agree, my point is merely that the bulk of the difference between idiomatic Java programs and idiomatic C++ programs is due to the wildly different ways of of programming idiomatically in Java vs. C++.

The small (steady state) performance difference remaining when doing the "exact same thing" in both programs is just down to how good the C++ compiler is vs. the VM JIT at optimizing (usually better, sadly).

What intrigues me about Rust is that hopefully we won't have to choose between readability and elegance vs. performance and safety. Keep up the good work.


It is very hard to have all this done reliably, especially in a rather dynamic language like Ruby. Maybe the Ruby VM could be better designed to perform these sort of optimisations, but it will never give the same control as a language like Rust, C or C++; i.e. a small code change could cause the optimiser to fail, leading to slow-down and bloat.

Furthermore, the hypothetical "sufficiently smart VM" isn't much value for code written now.


[Chris has done some fantastic work on a Truffle / Graal backend for jruby; for my part I'm (slowly) working on a "mostly-ahead-of-time" Ruby compiler]

I'm not sure I'd agree with "never", though I do agree Ruby is a hard language to optimize.

There are two challenges with optimizing Ruby: What people do and don't know the potential cost of, and what people pretty much never do, but that the compiler / VM must be prepared for.

The former includes things like "accidentally" doing things that triggers lots of copying (e.g. String#+ vs String#<< - the former creates a new String object every time); the latter includes things like overriding Fixnum#+, breaking all attempts at inlining maths, for example.

The former is a matter of education, but a lot of the benefits for many things are masked by slow VMs today that in many cases makes it pointless to care about specific methods, and an expectation not to think much about performance (incidentally, it's not that many years ago that C++ programmers tended to make the same mistakes en-masse)

The latter can be solved (there are other alternatives too), or at least substantially alleviated, in the general case by providing means of making a few small annotations in an app. E.g. we could provide a gem with methods that are no-ops for MRI but that signals to compilers that you guarantee not to ever do certain things, allowing many safeguards and fallbacks to be dropped.

Ruby's dynamic nature is an asset here in that there are many things where we can easily build a gem that provides assertions that on e.g. MRI throws an error if violated or turns into a no-op, but that on specific implementations "toggle" additional optimizations that will break if the assertions are not met. E.g. optional type assertions to help guide the optimizer for subsets of the app.

In other words: how optimized Ruby implementations we get depends entirely on whether people start trying to use Ruby for things where they badly need them.


Meta note: I saw that this post was being pretty heavily downvoted and upvoted it to keep it from falling out of the discussion. I disagree with the assumptions in the post, but they are handily refuted by replies. I'd rather have a robust discussion with every reasonable side well represented than a boring echo chamber.

I urge other folks here to not merely blindly downvote posts they disagree with, reserve downvoting for posts that don't deserve to be seen at all because they don't contribute to the discussion.


I've never built a Rails app, so perhaps there's something simple that I'm missing (I'm mostly a C# guy), but how would I use Skylight to monitor my on-premise application? The pricing makes it seems like a hosted service. I would have expected some sort of profiler to be needed on the server and then perhaps a centralized location for the data to be pushed to for display.

The design of the site is great and I'm mostly curious because it sounds like something I wish was available in the .NET world!


Thanks for asking. If you're interested in the nitty-gritty, Yehuda and I gave a talk on the architecture behind Skylight at RailsConf: http://www.confreaks.com/videos/3394-railsconf-how-to-build-...

The short version is that the agent runs on your servers and collects information from your Rails app using the ActiveSupport::Notifications instrumentation built in to the framework. We serialize that into a protobuf that's transmitted via IPC to a background daemon (written in Rust).

That daemon batches multiple reports into a single payload that is sent to the Skylight servers, where we use Storm and Cassandra to process the requests, and periodically do aggregate roll-ups.

Unlike New Relic, Skylight gives you access to the entire distribution of response times, not just the average response time. (According to DHH, averages are "useless.")[1] This ends up being a lot of data, and a lot of CPU-intensive processing, which is why we sell it as a hosted service.

[1]: https://signalvnoise.com/posts/1836-the-problem-with-average...


Minor point, but New Relic has had built-in support for collecting response time distributions for over a year. Please don't lie about this.

https://docs.newrelic.com/docs/apm/applications-menu/feature...


Just an FYI, while I think, to set up skylight I just add a gem to my project, I'm still not really sure. It would have been nice to go to your homepage and have it confirm that it is easy to configure/deploy into your application.


Is it possible to get the names of the Phd thesis read?


Hey Tom, did you also consider googles golang? Currently I'm building my backends with golang and I am pretty satisfied with the performance and the whole flow. Maybe it is sometimes a bit cumbersome to check on errors like a paranoid but in the long term it helps to predict what happens in error cases. How about rust? Is the workflow comparable to golang? Is there an equivalent to gofmt and some ide support for code completion? Thx and regards Bijan


I don't speak for tomdale/wycats, but embedding a language with a GC (Go) inside another GC'd language (Ruby) only leads to worlds of pain, especially when trying to efficiently transfer data between them.

In languages without compulsory GCs (like Rust, which doesn't have one at all) this works because it's easy to have complete control about when memory is freed, but a GC'd language may free memory that was passed back into Ruby since the GC can no longer find any references to it.

I'm sure there's ways around this (e.g. using unsafe/raw pointers), but this control is the default in Rust, and there are a pile of language mechanisms (ownership, in particular) that make making this safe much easier.

(Also, AIUI, Go's FFI story is relatively inefficient, and, has some rather bad bugs; apparently https://code.google.com/p/go/issues/detail?id=7978 is the Go GC trying to free FFI memory.)


Actually, that Go bug is the scanning code getting confused about an incorrectly stored stack pointer value during a very small race between returning from a FFI call into Go and generating a traceback for scanning. I'm not familiar enough with the internals to comment on if that can lead to freeing FFI memory, but I don't think so. Not that crashing the process is much better. :)


From what I understood, it's a Rust agent communicating protobuf structs over IPC, not embedded into the gem.

In such a case, memory safety and GC is less of an issue.


Memory safety is still good for long term code maintenance and refactorability. wycats also mentions that these processes are reasonably long lived - memory leaks can become a big problem over time if you are not careful. These can be mostly purged by static analysis and Valgrind, but are still a headache to deal with. I would also add that Rust is much easier to hack on safely if you don't have a great deal of prior systems programming experience.


I believe there is a Rust library embedded in the gem to serialize and communicate with the outside agent (IIRC, this is actually the most important part to be in Rust, it needs to be efficient to avoid interfering with the normal operation of the main program as much as possible).


I've never looked at it too closely, but wycats has talked about how the Ruby code calls Rust code through the FFI and how Skylight doing some special things to make that work especially smoothly by directly calling some internal functions of Rust's failure handling bits, and about how the Rust code crashing shouldn't take down the rails process. That seems to suggest it's not just an IPC thing.


There are some work-in-progress code completion tools https://github.com/phildawes/racer).

No format tool yet, but its often talked about and Id be surprised if it doesnt happen.

The biggest infrastructure difference to go at the moment is that its tricky to cross compile binaries in rust.


From time to time I use "rustc --pretty normal <file.rs>". Not a real formatting tool, and it has a tendency to produce some funny results at times, but it's better than nothing.




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