220: Improve Rails perf 5-10x

Yes,

it uses lightweight Fibers instead of Threads to handle concurrency, so it allows more db operations per process
Removed unused middlewares
Removed prometheus http collector, it adds around 20% and not used in node, send a patch to the prom client with improvement https://github.com/prometheus/client_ruby/pull/316, I guess it can be improved further

Final results for create endpoint, it is not 10x, only 3x RPS and 8x better latency

before:
wrk -c 100 -t 2 -d 10 --latency -s ruby-app/wrk.lua http://localhost:8080/api/devices
Running 10s test @ http://localhost:8080/api/devices
  2 threads and 100 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency   163.18ms  205.32ms   1.09s    80.02%
    Req/Sec     0.90k   210.50     1.21k    77.00%
  Latency Distribution
     50%    7.90ms
     75%  314.85ms
     90%  474.04ms
     99%  809.52ms
  17954 requests in 10.01s, 11.95MB read
Requests/sec:   1793.34
Transfer/sec:      1.19MB

after:
wrk -c 100 -t 2 -d 10 --latency -s wrk.lua http://localhost:8080/api/devices
Running 10s test @ http://localhost:8080/api/devices
  2 threads and 100 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency    20.20ms   11.63ms 137.45ms   91.93%
    Req/Sec     2.66k   647.28     3.45k    86.00%
  Latency Distribution
     50%   17.30ms
     75%   20.61ms
     90%   26.89ms
     99%   76.76ms
  52996 requests in 10.04s, 16.88MB read
Requests/sec:   5277.25
Transfer/sec:      1.68MB

antonputra / tutorials

220: Improve Rails perf 5-10x #335