[erlang-questions] (Googl never Erlanged) Rewriting a large production system in Go (matt-welsh.blogspot.com)

Loïc Hoguin <>
Tue Aug 20 09:26:49 CEST 2013


Why do you paste us HN discussions? There's no better waste of time than 
to read programmers comparing "sizes".

On 08/20/2013 07:02 AM, giovanni_re wrote:
> https://news.ycombinator.com/item?id=6234736
> Rewriting a large production system in Go (matt-welsh.blogspot.com)
> 222 points by qdie 1 day ago | 173 comments
> http://matt-welsh.blogspot.com/2013/08/rewriting-large-production-system-in-go.html
>
> MW: PhD U. Cali Forni Berkeley
>
>
>
> ==========  https://news.ycombinator.com/item?id=6234736
> derefr 1 day ago | link You know, every time I see some Googler shocked
> at the effectiveness and various advantages of coding in Go, I wonder
> why Google never adopted Erlang. They could have been getting all these
> same advantages (and then some) a decade ago :)
>
> reply
>
> [GR:  Would Googl use an Erlang on its' search engine show?]
>
>
>
>
> zaphar 1 day ago | link (full disclosure: I work at google and also like
> erlang) Erlang has fantastic facilities for robustness and concurrency.
> What it does not have is type safety and it's terrible at handling text
> in a performant fashion. So if you don't care about either of those
> things and only care about robustness and concurrency then Erlang is
> great. There were internal discussions about Erlang here but the upshot
> was. We had already basically duplicated Erlangs supervision model in
> our infrastructure, only we did it for all languages and Erlang didn't
> offer any benefits in performance for us. It's only benefit would have
> been the concurrency model. That's much less benefit than Go gives. Go
> gives you Erlangs concurency model, a similar philosophy of robustness,
> type safety, all batteries included, and performance. Equating the two
> languages works in 1 or 2 dimensions but not on all the dimensions
> google cares about.
>
> reply
>
> derefr 1 day ago | link Interesting, thanks for that; it's pretty much
> what I guessed (especially the bit about the supervision tree and
> hot-code-upgrade advantages being mooted by your infrastructure.) On a
> tangent, though: > What it does not have is type safety I've tried to
> work this out before (I'm designing a new language for Erlang's VM), but
> as far as I can tell, type safety is in practice incompatible with
> VM-supported hot code upgrade. If you have two services, A and B, and
> you need to upgrade them both, but you can't "stop the world" to do an
> atomic upgrade of both A and B together (because you're running a
> distributed soft real-time system, after all), then you need to switch
> out A, and then switch out B. So, at some point, on some nodes, A will
> be running a version with an ABI incompatible with B. In a
> strongly-typed system, the VM wouldn't allow A's new code to load, since
> it refers to functions in B with type signatures that don't exist. On
> the other hand, in a system with pattern-matching and a "let it crash"
> philosophy, you just let A's new code start up and repeatedly
> try-and-fail to communicate with B for a while, until B's code gets
> upgraded as well--and now the types are compatible again. It's an
> interesting problem.
>
> reply
>
> laureny 1 day ago | link > type safety is in practice incompatible with
> VM-supported hot code upgrade. That's not true. First, it's very easy to
> hot reload changes that have been made to the code that are backward
> compatible. The JVM spec describes in very specific details what that
> means (adding or removing a method is not backward compatible, modifying
> a body is, etc...). This is how Hotswap works, the JVM has been using it
> for years. As for changes that are backward incompatible, you can still
> manage them with application level techniques, such as rolling out
> servers or simply allow two different versions of the class to exist at
> the same time (JRebel does that, as do other a few other products in the
> JVM ecosystem). Erlang doesn't really have any advantages over
> statically typed systems in the hot reload area, and its lack of static
> typing is a deal breaker for pretty much any serious production
> deployment.
>
> reply
>
> rdtsc 20 hours ago | link > lack of static typing is a deal breaker for
> pretty much any serious production deployment. Are you talking about
> Google only where they made it a mandate or in general? There are
> serious production deployments on Python, Ruby, Erlang and Javascript. I
> will trade expressiveness and less lines of code with a strong but
> dynamically typed language + tests over more a static typed language
> with more lines of code all being equal. Or put it another way, if
> strong typing is the main thing that protects against lack of faults and
> crashes in production, there is a serious issue that needs to be
> addressed (just my 2 cents).
>
> reply
>
> derefr 23 hours ago | link > As for changes that are backward
> incompatible, you can still manage them with application level
> techniques, such as rolling out servers or simply allow two different
> versions of the class to exist at the same time (JRebel does that, as do
> other a few other products in the JVM ecosystem). Neither of these allow
> for the whole reason Erlang has hot code upgrade in the first place:
> allowing to upgrade the code on one side of a TCP connection without
> dropping the connection to the other side. Tell me how to do that with a
> static type system :)
>
> reply
>
> pmahoney 10 hours ago | link Tomcat (and other app servers) has support
> for doing hot reloads of Java web apps while not reloading the HTTP
> layer (and not dropping TCP connections).
> http://www.javacodegeeks.com/2011/06/zero-downtime-deploymen... I have
> implemented a similar system for JRuby apps running inside a Servlet
> container. There are many caveats. I don't actually recommend it because
> for a while you're using nearly twice the memory (and JRuby is
> particularly memory hungry). Also there are many ways to leak the old
> class definitions such that they are not GC'd (e.g. thread locals). But
> it's certainly possible. I suspect that Erlang, Java, and all languages
> are in the same boat: some parts can be upgraded live in the VM while
> other parts require a full restart (maybe coordinating with multiple
> nodes and a load balancer to achieve zero-downtime).
>
> reply
>
> lenkite 10 hours ago | link Out of curiosity, where/why would such an
> exotic feature be needed in today's internet architectures where you
> always front a group of servers with a load balancer ?
>
> reply
>
> butterflyhug 5 hours ago | link Not all Internet protocols are HTTP. If
> you're running a service where long-lived connections are the norm,
> "simply fronting a bunch of servers with a load balancer" can require a
> pretty smart load balancer. E.g. IMAP connections often last hours or
> even days, and are required to maintain a degree of statefulness.
>
> reply
>
> DanWaterworth 1 day ago | link Go gives you Erlangs concurency model
> There are a number of significant differences between Erlang's and Go's
> concurrency models: Asynchronous vs synchronous communication,
> per-thread vs per-process heaps, send to process vs send to channel.
>
> reply
>
> dbaupp 1 day ago | link Go doesn't have strong type safety either; I
> remember a recent story about a Go stdlib function "accidentally"
> calling an interface it shouldn't.
>
> reply
>
> f2f 22 hours ago | link it wasn't accidental -- it was written on
> purpose by a programmer (a conversion from Writer to WriteCloser). it
> was immediately acknowledged as an error and eventually may be caught by
> the standard code examining tool "vet".
>
> reply
>
> pcwalton 22 hours ago | link What would the static analysis that "vet"
> is performing enforce to stop this? No interface-to-interface downcasts?
>
> reply
>
> .....
> [It goes on, & on, & on & on,
> when Go & Erlang party together.]
>
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-- 
Loïc Hoguin
Erlang Cowboy
Nine Nines
http://ninenines.eu


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