Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

A Brief Guide to OTP in Elixir

serokell.io

Post reply on HN
Print view View original

31–40 of 100 posts

Re: A Brief Guide to OTP in Elixir

#31

Post by toast0 »

rozap wrote: post #23
nickjj wrote: post #9

> Forget using a million different technologies for things like background jobs, OTP can supply you with everything. It's true but in practice this usually doesn't pan out. For example with just background jobs alone there's the idea of queues, tracking failures / successes, exponential back-off retries, guaranteeing uniqueness, draining, periodic tasks and everything else you'd likely want in a production ready app.…

I think these blog posts usually pretend it's simpler than it is. There's usually (almost always) durable storage required somewhere. But to respond to your example specifically, OTP offers quite a bit. To your points: Queues: a coordinator genserver process per node, which uses poolboy to only run X jobs at a time Tracking failures/sucesses: postgres Exponential backoff: a function Uniqueness across the cluster: std…

> There's usually (almost always) durable storage required somewhere.

Despite the name, mnesia can provide durable storage, without using anything outside of OTP and your nodes' (hopefully durable) filesystems.

Re: A Brief Guide to OTP in Elixir

#32

Post by [deleted] »

rectang wrote: post #30
abetlen wrote: post #3

OTP = Open Telecom Platform [1], though I think the full name is avoided nowadays. On an unrelated note, I've always been fascinated with the Erlang VM. The idea that you could hot-load modules and have multiple versions of the same module running at once seems really useful. I wonder why other runtimes haven't adopted these features? [1] https://en.wikipedia.org/wiki/Open_Telecom_Platform

Or "One Time Password" if you're an idiot like me. Gotta love an introductory article on "OTP" which even includes a section entitled "What is OTP?" but doesn't expand the acronym.

[deleted]

Re: A Brief Guide to OTP in Elixir

#33

Post by toast0 »

thelazydogsback wrote: post #21

I assume because every process has its own GC that messages are always copied, even on the same node? AFAICT, there is no shared/copy-on-write messages in the BEAM, except for a few cases where you explicitly pass a shared byte buffer for special circumstances? I would think this is worth the cost in most cases, but for some workloads would be prohibitive.

Some binaries (byte buffers as you called them) are stored outside the process heap, and those are messaged by reference, not by copying; but all other terms are messaged by copying. This is a lot of copying, but it makes the GC very simple, so it's usually a positive tradeoff. Although, there's probably some use cases where it's not great. For those, it might makes sense to force things into the off process heap binaries (RefC), or possibly by doing terrible things with native code (Nifs). You might also put things into the included key-value memory storage (ets), and more selectively pull things out to avoid copying a large chunk data to every process that needs a small piece.

Re: A Brief Guide to OTP in Elixir

#34

Post by riquito »

toast0 wrote: post #31
rozap wrote: post #23

Earlier quoted context omitted.

I think these blog posts usually pretend it's simpler than it is. There's usually (almost always) durable storage required somewhere. But to respond to your example specifically, OTP offers quite a bit. To your points: Queues: a coordinator genserver process per node, which uses poolboy to only run X jobs at a time Tracking failures/sucesses: postgres Exponential backoff: a function Uniqueness across the cluster: std…

> There's usually (almost always) durable storage required somewhere. Despite the name, mnesia can provide durable storage, without using anything outside of OTP and your nodes' (hopefully durable) filesystems.

Despite? It pretty much means "to remember", it doesn't have the alpha privative of amnesia, "to forget"

Re: A Brief Guide to OTP in Elixir

#35

Post by Thaxll »

abetlen wrote: post #3

OTP = Open Telecom Platform [1], though I think the full name is avoided nowadays. On an unrelated note, I've always been fascinated with the Erlang VM. The idea that you could hot-load modules and have multiple versions of the same module running at once seems really useful. I wonder why other runtimes haven't adopted these features? [1] https://en.wikipedia.org/wiki/Open_Telecom_Platform

Because why would you do that? Now we have tool and pipeline where testing / deploying ect .. is easy, so I'm not sure why would I risk to do hot load things.

I don't think it's useful and I think it's pretty dangerous is the first place. You have code that can run two different things, wcgw.

Re: A Brief Guide to OTP in Elixir

#36

Post by dnautics »

rectang wrote: post #30
abetlen wrote: post #3

OTP = Open Telecom Platform [1], though I think the full name is avoided nowadays. On an unrelated note, I've always been fascinated with the Erlang VM. The idea that you could hot-load modules and have multiple versions of the same module running at once seems really useful. I wonder why other runtimes haven't adopted these features? [1] https://en.wikipedia.org/wiki/Open_Telecom_Platform

Or "One Time Password" if you're an idiot like me. Gotta love an introductory article on "OTP" which even includes a section entitled "What is OTP?" but doesn't expand the acronym.

It's no longer considered a correct acronym as erlang is not really a telecoms language anymore. It's been a problem where outsiders are quick to think or say, "I am not writing a telecoms app" and dismiss it.

Re: A Brief Guide to OTP in Elixir

#37

Post by dnautics »

jeremyjh wrote: post #2

I'd just like to point out that while knowledge of OTP is a good thing for an Elixir developer, it isn't really needed for most application development. There are excellent libraries and frameworks that leverage OTP to provide a lot of value to their users, and most of us who use Elixir in industry just use those libraries.

I would go so far as to say a beginner should not write genservers, and using genservers that aren't part of a library is usually an antipattern. When you're ready to write a serious library, then you're ready to write genserver.

Of course it's always good to understand genservers.

Re: A Brief Guide to OTP in Elixir

#38

Post by dnautics »

tlack wrote: post #29
pmontra wrote: post #5

> In real life, we don’t need to write code with receive do loops. Instead, we use one of the behaviours created by people much smarter than us. I make more than half of my income from Elixir. That said, the naive receive loop is much easier to understand than any of the GenServer examples. They pollute the module logic with all that handle_* boilerplate. I believe that neither Erlang nor Elixir got the right abstrac…

What you said is rarely stated in public, but I've often felt it too: OTP obscures the underlying beauty of the Erlang platform. OTP is well engineered of course, but the basic notion of the spawn -> receive -> loop cycle is so clean and illuminating that I wish newbies would hold out before learning OTP sometimes. It's natural to think of case-specific abstractions around the primitives that are more germane to the…

Yeah but that's like saying the awkwardness of stl templates obscures the beauty of C++ or the Android app api obscures the beauty of the jvm. The genserver is messy because it deals with a good chunk of messiness around safely managing distributed systems for you. It probably could be improved (Dave thomas critiques comes to mind) but elixir had to be conservative because if it weren't it wouldn't have had buy in from the beam community and wouldn't have become the first truly successful non-erlang language targeting the BEAM.

Re: A Brief Guide to OTP in Elixir

#39

Post by dmitriid »

Thaxll wrote: post #35
abetlen wrote: post #3

OTP = Open Telecom Platform [1], though I think the full name is avoided nowadays. On an unrelated note, I've always been fascinated with the Erlang VM. The idea that you could hot-load modules and have multiple versions of the same module running at once seems really useful. I wonder why other runtimes haven't adopted these features? [1] https://en.wikipedia.org/wiki/Open_Telecom_Platform

Because why would you do that? Now we have tool and pipeline where testing / deploying ect .. is easy, so I'm not sure why would I risk to do hot load things. I don't think it's useful and I think it's pretty dangerous is the first place. You have code that can run two different things, wcgw.

A very erlang demo showed upgrading code running on a telephone switch without dropping the call. That's why you want hot code loading.

Re: A Brief Guide to OTP in Elixir

#40

Post by dnautics »

Thaxll wrote: post #35
abetlen wrote: post #3

OTP = Open Telecom Platform [1], though I think the full name is avoided nowadays. On an unrelated note, I've always been fascinated with the Erlang VM. The idea that you could hot-load modules and have multiple versions of the same module running at once seems really useful. I wonder why other runtimes haven't adopted these features? [1] https://en.wikipedia.org/wiki/Open_Telecom_Platform

Because why would you do that? Now we have tool and pipeline where testing / deploying ect .. is easy, so I'm not sure why would I risk to do hot load things. I don't think it's useful and I think it's pretty dangerous is the first place. You have code that can run two different things, wcgw.

I think (could be wrong) it's used for hot code reloading in phoenix when you're in dev mode. Make a change in your code, hit refresh in the browser, and now the relevant code deltas are applied to your http request.
Post reply on HN