What is the difference between the way Ruby and Erlang processes are scheduled? I explore the differences in latency and where this can lead to issues in industries like payments.

1. Erlang vs Ruby
Preemptive Scheduling

2. Ruby
Virtual Machine: YARV
Application Server: Phusion Passenger
Web Server: Nginx
Server: Digital Ocean 2 cores and 2 GB RAM

3. Erlang
Virtual Machine: BEAM
Web Server: Cowboy
Server: Digital Ocean 2 cores and 2 GB RAM

4. Basic Architecture
Server
Apache
Benchmark
HTTP AUTH
Hello, Alladin!
5’ Processing

5. SOA Architecture
Ruby
Server
Apache
Benchmark
HTTP AUTH
Hello, Alladin!
Ruby
Service
Req
Resp

6. 50 concurrent requests
Erlang Ruby
ab -n 50 -c 50 -A “username:password” <server>

7. Discussion
Erlang response time approx. constant
Ruby response time increasing (~900 ms / req)

8. Scheduling: Erlang (BEAM)
Preemptive Scheduling
Runs 2000 reductions and then processes the next task
“In computing, preemption is the act of temporarily interrupting a task being carried out by a computer system,
without requiring its cooperation, and with the intention of resuming the task at a later time. Such a change is known as
a context switch. It is normally carried out by a privileged task or part of the system known as a preemptive scheduler,
which has the power to preempt, or interrupt, and later resume, other tasks in the system.” https://en.wikipedia.
org/wiki/Preemption_(computing)
Light weight processes
Runs each process as a thread, allowing for a plethora of processes.

9. Scheduling: Ruby (YARV)
One Thread per Process
passenger_thread_count “The default value is 1.”
This value can be increased in the Enterprise version
Most Ruby servers are running one thread per process

10. Conclusions
Ruby requires horizontal scaling
Ruby requires tuning
Erlang can handle scaling
Erlang handles these problems by default
Payment providers with a fixed amount of cores should use Erlang

11. Thank you
Markus Feyh
markus.feyh@gmail.com