Why and How I Switched from Python to Erlang

Sure, np. I am mainly an Erlang developer but the same properties apply to Elixir, because both share the same battle tested VM -- BEAM.

> I'm asking what kind of web apps or scenarios do you think Elixir is particularly well suited for?

I am not currently working on building web app directly. But in general Elixir/Erlang would be good for a scenario where they'd be multiple connected clients at the same time. Think maybe something like a car sharing service where map updates in realtime as cars move through the city. Lots of users chatting together, or playing a game. Maybe they are bidding on ads, or tagging posts with "likes" and so on.

But there might be a significant improvemtent even in the plain old request-goes-to-database scenario, simply because the VM (BEAM) is better equipped at handling multiple connected sockets, all streaming data in and out. For example, it knows how to take advantage of multiple CPU cores, it handles GC better and so on. Not sure how deeply you want this explanation to go, so will stop here.

But, yes, if it all goes to a single MySQL instance running in another datacenter, that might be the bottleneck so there might not be a speedup seen by using something else. So you have to measure. In that case maybe a cache in front of it will work just as well to speed things up.

> he was doing away with the db completely.

Haven't seen the video. But with Erlang can think of those processes as in-memory storage of state. Can spawn hundreds of thousands of them, and they can live as long as the node stays up. Then can also connect multiple BEAM VM instances on different machines, create a cluster and so can refer to these processes as if they are local, in a rather transparrent manner. Or maybe they mean they used Erlang's built-in database (Mnesia), that had some limitations, but recently in a new release (19.0) it has the ability to scale much better as it can handle a pluggable storage such as LevelDB for example. The advantage there is the database is integrated into the langauge. So queries are not in a different query language, via a driver, so some other process, but queries looks like list comprehensions and transactions are just function closures. That can simplify things immensly in some cases.

> how do you architect your application in Elixir to keep application state though multiple requests (sessions) on multiple boxes without using something like memcached or redis (or a network disk)?

Can create a cluster so can keep state on another node that doesn't go down? (as mentioned), or can still use a database (say Postgres), so it really depends. Hard to give a general advice here.

select * from visits, plus conversion to JSON and delivery to a client on local loop. About 5000 records.

* Phoenix 140 ms

* Rails 248 ms

* Ruby without AR 219 ms

* PostgreSQL 2.97 ms, with no JSON generation and no delivery

select started_at, duration from visits -- JSON and delivery

* Phoenix 74 ms

* Rails 116 ms

* Ruby without AR 88 ms

* PostgreSQL 3.47 ms, no JSON no delivery

Single process, so maybe Phonix could get a larger advantage as the number of processes/requests increase. For the typical none to low traffic site there is little difference, the tool the programmer is more familiar with wins.

Edit: improved formatting.

2) db is rarely your problem. Interpretation can be, and tons of other things. Also erlang schedules things far better and use all the core of the machine, so it will block far less, etc It also means that the thourgput and latency will stay stable despite the amount of users growing. (up to a limit, but it will far higher)

3) Store it in memory. And link other node to yours. Tadaaa

4) Where data live depends of your use case but why use a db if you do not need it anyway?

The thing in general is that web framework tend to use db to hide concurrency.

Also why no cache : because cache is complex, cost you another dependency and another program, make debugging harder, make your app less deterministic, etc. If you need cache use it. But caching is a really hard thing.

My experience with Go has been that it is almost as easy to get it up and running just as fast as with Python.

To be clear, are you suggesting that's reasonable to do a rewrite (or at least for certain parts) from Python/Ruby when you need to scale? Is that going to be reasonably accomplishable in many cases? Honest question. Just wondering what you have in mind.

Alright -- I'll bite.

Rarely anyone "needs to scale." Plenty of $1B businesses can succeed on a fistful of c4.large's running Ruby on Rails. The same Ruby on Rails that ran their MVP. Scaling via language change isn't the path to victory, unless you picked a language that was poorly suited to your domain to begin with.

Too many companies end up following this cargo-cult advice, and spend more time grappling with their tools than innovating. Because "concurrency." Someday.

Optimizing your choice of language for anything other than a linear relationship between Real Complexity and Implementation Time is a fool's errand and a fiduciary travesty.

In all fairness, Elixir/Phoenix could become as well-learned as Ruby on Rails. We'll end up in a best-of-both-worlds scenario. And at that point, I'll happily eat my words.

But in the meantime, solve your "scaling" problems by measuring and optimizing, instead of re-writing your app in the flavor-of-the-week.

Among the languages you cited, C# has async/await, Clojure has core.async, Elixir has processes and messages, Go has goroutines and channels, but the other languages (Python, Ruby, Java, Rust) have nothing built-in specifically related to concurrency, do they?

This is all of course compared to the current buzz surrounding Elixir/Phoenix. I didn't intend to dismiss Erlang's amazing track record and applications to the domains where it continues to shine.

This is roughly the time span I was referring to when I said "buzz":

https://hn.algolia.com/?query=erlang&sort=byPopularity&prefi...