A lot of people are hitting on the performance improvements (25 Sidekiq threads/workers versus 10k-100k+ Elixir/Erlang processes) but when I find myself doing this it's actually because my background process flows are really complex. The drastic increase in concurrency is just the cherry on top.
Background work is asynchronous by nature and often times you have dependencies between jobs, groups/batches jobs and also need robust error handling/recovery. This is where Elixir/Erlang really shines and using Actors & OTP to model these complex flows is the huge win in my experience. Sidekiq Pro offers support for batches which covers some of this, but ultimately Elixir/Erlang processes are just a huge improvement in modeling such systems.
A concrete example is sending off 10 jobs. When all 10 are done, move on to the next step. Each of these 10 jobs can also send data to the waiting step which it can then use as arguments. If any job should fail N times, cancel and rollback all of the jobs and try again. After the next step, split those 10 jobs into two groups of 5 and do those 5 sequentially. So on and so forth. Try doing this in Ruby. You'll likely have to manage your own data structures in Redis. In Elixir you just use GenServers and sometimes ets tables. It's all handled in the language itself, rather than external data stores.
Sidekiq is probably suitable for 90% of Ruby apps doing basic fire and forget and batching with Sidekiq Pro. But if your domain has seriously complicated background processing, use a tool more suited for that.
We're a mobile game company, and we use C, C#, Objective C, Java, Python, Go, Erlang, JavaScript, Lua, and more where they make sense.
I love language talk and debates (and hate the language hate) here on HN. But if you're only using a single language in production, you're likely not that big, or more likely have a lot to gain by reworking certain bits with other technologies where they make sense.
It is like "I only do hammers and nails. For drilling ask the guy over there."
EDIT: Also your example of polling on Redis queue using elixir is very inefficient and makes your article not so credible in my eyes or eyes of other good software architects. Redis is meant for pub sub and not polling.
One minor suggestion for the author (post doesn't have a comment section). `:timer.sleep(10)` is explained as "sleep for 10 seconds", but sleep takes millis as an argument (http://www.erlang.org/doc/man/timer.html#sleep-1).
If the job involves an expensive API call it will tie up a worker for the duration of the call.
So it's not so much ~thousands of jobs per second as it is a limitation of only 10 ruby processes per 1GB of memory. (A ruby process with the Rails env loaded is about 100MB.)
Elixir gives you the ability to make a few orders of magnitude more calls in a tiny amount of memory. (100,000 Elixir "workers" can be had in less than 1GB).
tl;dr - Sidekiq can do a LOT of work, even on MRI with the GIL.
I totally agree that each language has its strength and each facet of your problem may best be solved in a different language.
Similarities don't go much further than def do end (but there are too many do and too many different def in Elixir) and the sensible naming of some Library.functions() to match classes and methods in Ruby's standard library. But hey, making a good first impression is extremely important and Elixir has been engineered well in that regard. It's not one of those I'll-never-ever-be-able-to-read-it languages.
