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Refactoring Ruby with Monads

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Re: Refactoring Ruby with Monads

#31

Post by codygman »

zimbatm wrote: post #26

Recently I benchmarked a small network server written in Haskell. During the load testing the GHC runtime would allocate at rates of 1.6GB/s which is highly unusual from my experience but is apparently normal for pure functional languages. The impressive bit is that during the operations the heap was never bigger than 50MB and GC pauses longer than 100ms. If we where to re-write all our ruby code to be purely functio…

Small network server? Was it a custom one or one you got from somewhere? I know for a fact that wai, warp, and snap-server are way faster than that.

Re: Refactoring Ruby with Monads

#32

Post by samnardoni »

imanaccount247 wrote: post #29
zimbatm wrote: post #26

Recently I benchmarked a small network server written in Haskell. During the load testing the GHC runtime would allocate at rates of 1.6GB/s which is highly unusual from my experience but is apparently normal for pure functional languages. The impressive bit is that during the operations the heap was never bigger than 50MB and GC pauses longer than 100ms. If we where to re-write all our ruby code to be purely functio…

>but is apparently normal for pure functional languages Where did you hear that? >and GC pauses longer than 100ms. Yikes! That is not normal at all. You wouldn't be able to write a decent webserver in haskell if that were normal.

I think he/she meant the GC pauses were never longer than 100ms.

Re: Refactoring Ruby with Monads

#33

Post by imanaccount247 »

samnardoni wrote: post #32
imanaccount247 wrote: post #29

Earlier quoted context omitted.

>but is apparently normal for pure functional languages Where did you hear that? >and GC pauses longer than 100ms. Yikes! That is not normal at all. You wouldn't be able to write a decent webserver in haskell if that were normal.

I think he/she meant the GC pauses were never longer than 100ms.

Yes, and getting anywhere close to 100ms is not normal at all. Warp benchmarks show total request latency never goes above 50ms or so, a 100ms gc pause would be very apparent.

Re: Refactoring Ruby with Monads

#34

Post by merijnv »

zimbatm wrote: post #26

Recently I benchmarked a small network server written in Haskell. During the load testing the GHC runtime would allocate at rates of 1.6GB/s which is highly unusual from my experience but is apparently normal for pure functional languages. The impressive bit is that during the operations the heap was never bigger than 50MB and GC pauses longer than 100ms. If we where to re-write all our ruby code to be purely functio…

The reason GHC allocates at such an aggressive rate is the fact that memory allocation is really cheap in GHC. Allocating memory on the GHC heap is literally just bumping the "top of heap ptr", so writing one word.

The idea is that 90% of allocations are very short-lived, so allocating a ton doesn't matter as long as you can throw it away cheaply. Suppose we have an inner loop over an array, summing values. We may allocate at 1.6 GB/s doing the computation, but everything except the last value is garbage.

When we GC we simply copy this last value from the current heap and reset the "top of heap pointer". Yet another cheap operation.

There's a lot more going on (generational GC, nursery's and what not), but GHC's GC heavily abuse some facts that, for example, CRuby cannot, such as the fact that older generations can never reference data in newer generations, so GCing the current generation never has to perform "major GC" (i.e. checking the older data whether it still needs the current generation).

Re: Refactoring Ruby with Monads

#35

Post by theflubba »

actsasbuffoon wrote: post #6
vinceguidry wrote: post #2

Please don't actually do this. Ruby is not a functional language, if your project really needs to be functional all the way through just use Haskell or whatever. Otherwise just pull out the parts of your code would benefit from being expressed in functional style into a module and work on implementing a proper DSL.

Monads are useful even in imperative languages. They're just a context with a way of specifying how actions get chained together. Scala, Swift, and a number of other imperative languages have adopted monads (like Maybe) to great effect. Conversely, the state monad (for example) has seen less adoption. Probably because it's a little difficult to grasp, and imperative languages just rely on mutable state for a similar…

No. Scala is a very functional language that you can write imperative code with. Swift is not functional and doesn't have real monads. Ruby monads are just a way of obfuscating your code. Monads are more than the monadic bind >>=. You cannot just use monads and ignore the rest of category theory, it's like using a stick to fix the engine of a car. Useless. Just use a real functional language so you don't have to deal with this tomfoolery.

Example of a real monad: http://www.haskell.org/haskellwiki/Monad

Re: Refactoring Ruby with Monads

#36

Post by theflubba »

zimbatm wrote: post #26

Recently I benchmarked a small network server written in Haskell. During the load testing the GHC runtime would allocate at rates of 1.6GB/s which is highly unusual from my experience but is apparently normal for pure functional languages. The impressive bit is that during the operations the heap was never bigger than 50MB and GC pauses longer than 100ms. If we where to re-write all our ruby code to be purely functio…

Because, you failed to properly set up GHC, you don't have the right to say anything about Haskell or functional programming.

Re: Refactoring Ruby with Monads

#37

Post by zimbatm »

codygman wrote: post #31
zimbatm wrote: post #26

Recently I benchmarked a small network server written in Haskell. During the load testing the GHC runtime would allocate at rates of 1.6GB/s which is highly unusual from my experience but is apparently normal for pure functional languages. The impressive bit is that during the operations the heap was never bigger than 50MB and GC pauses longer than 100ms. If we where to re-write all our ruby code to be purely functio…

Small network server? Was it a custom one or one you got from somewhere? I know for a fact that wai, warp, and snap-server are way faster than that.

A custom non-HTTP TCP server with STM and forkIO

Re: Refactoring Ruby with Monads

#38

Post by zimbatm »

imanaccount247 wrote: post #33
samnardoni wrote: post #32

Earlier quoted context omitted.

I think he/she meant the GC pauses were never longer than 100ms.

Yes, and getting anywhere close to 100ms is not normal at all. Warp benchmarks show total request latency never goes above 50ms or so, a 100ms gc pause would be very apparent.

It's from memory, it's possible that the major GC where around 50ms. Minor GC where around 5ms for sure.

Re: Refactoring Ruby with Monads

#39

Post by zimbatm »

theflubba wrote: post #36
zimbatm wrote: post #26

Recently I benchmarked a small network server written in Haskell. During the load testing the GHC runtime would allocate at rates of 1.6GB/s which is highly unusual from my experience but is apparently normal for pure functional languages. The impressive bit is that during the operations the heap was never bigger than 50MB and GC pauses longer than 100ms. If we where to re-write all our ruby code to be purely functio…

Because, you failed to properly set up GHC, you don't have the right to say anything about Haskell or functional programming.

It's the Internet, why wouldn't I write about my experience ?

And I'm sure it's possible to tune GHC. The argument is that if you're going to write immutable data structures in ruby then there is going to be more GC pressure. I don't think it's possible to optimise the ruby GC anywhere near the GHC one because of the mutable nature of the language.

Re: Refactoring Ruby with Monads

#40

Post by zimbatm »

imanaccount247 wrote: post #29
zimbatm wrote: post #26

Recently I benchmarked a small network server written in Haskell. During the load testing the GHC runtime would allocate at rates of 1.6GB/s which is highly unusual from my experience but is apparently normal for pure functional languages. The impressive bit is that during the operations the heap was never bigger than 50MB and GC pauses longer than 100ms. If we where to re-write all our ruby code to be purely functio…

>but is apparently normal for pure functional languages Where did you hear that? >and GC pauses longer than 100ms. Yikes! That is not normal at all. You wouldn't be able to write a decent webserver in haskell if that were normal.

    > but is apparently normal for pure functional languages
    Where did you hear that?
It's certainly true for Clojure as well. My guess is that it applies to any language that uses immutable data structures. I remember Rich Hickey talking about issues with the JVM due to clojure's unusual allocation model in one of his talks.
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