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

giovanni_re <>
Tue Aug 20 07:02:20 CEST 2013


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 :)

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[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.

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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.

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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.

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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).

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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 :)

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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).

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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 ?

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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.

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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.

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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.

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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".

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pcwalton 22 hours ago | link What would the static analysis that "vet"
is performing enforce to stop this? No interface-to-interface downcasts?

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.....
[It goes on, & on, & on & on,
when Go & Erlang party together.]

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