[erlang-questions] What do you like the most about Erlang/OTP?

Mike Oxford <>
Wed Aug 29 07:13:46 CEST 2012


On Tue, Aug 28, 2012 at 8:56 PM, Garrett Smith <> wrote:

> So you get systems that run effectively with less code, less testing,
> and less maintenance.
>
> I'd be curious how many people, based on their experience building
> production Erlang systems, would agree or disagree with this.
>

I believe you're treading dangerous territory here.  :-)

There is less custom code...but such is the case with any framework.
There is less testing ONLY due to less volume of code, which is the case
with any framework.
There is less maintenance due to ... you guessed it, less volume of code.

So, really, you're looking at "Framework vs Non-Framework."

What "sold me" on erlang originally was:
1)  Distributed was "easy."
2)  Shared-state was built-in
3)  No downtime code deployments
4)  Supervisors

The reality:
1)  Distributed is easy, kinda.  Easier.  Getting a message to another node
is trivial, which is what Erlang does and from then on it's
application-level code (eg, you still have to write it and do work. :)

2)  Shared state is done via mnesia.  House of cards, IMO, having run it.
 It's just too fragile as-is.  One node burps and your whole database goes
into a corner, sucking its thumb until you fix it.  Ulf's unsplit is a good
start, but given current-state I'd have to say it's too risky to run in
production for anything without a back-plane network.  Split-brain is hard
-- may be that wedging Riak in would work here (Ulf's unsplit uses
vector-clocks, inspired by Riak.)  It would be nice if mnesia at least said
"node dead is dead, let the rest run even if the first comes back."  We had
a 3-node cluster and one node would burp and all three nodes would fail to
run.  Setting master-node works but then you start going down the "not
fully distributed" route.  Majority helps ... until a node comes back.  If
you have 30 nodes and one goes down and comes back...both have node-down
states and your whole set of 29 runs to the corner....  Majority + Unsplit
+ Master is about the best you can get, until your partition falls along
Master-lines and when you come back 20+ nodes are all doing copies off the
master to sync up.  8-)  I really like mnesia...really really, and I really
really tried to shoehorn it in.  Maybe I'm doing something wrong, but I see
similar issues with RabbitMQ's use of mnesia so I don't think I'm too far
off.  I would love to be shown incorrect here....please?  Anyone?

3)  These are hard.  Doable, but you end up with a LOT of testing of the
upgrade/downgrade paths.  You start questioning the value vs "rolling
restarts."  It's a golden-hammer when you need it, though you have to
really look at the value and "cost" of using such a weapon regularly
(testing time vs just rolling restarts.)

4)  #winning =:= #winning    Love 'em.

That said, Erlang has become my personal "gold standard" for other
languages, and by which I judge all others.  :)

-mox
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