Hacker News Reader

Rails 4 is thread safe and I used puma as server Also the app is in production mode and the db pool is 16

Can you post a link to the app? Have you considered running the TechEmpower benchmark app? https://github.com/TechEmpower/FrameworkBenchmarks

Rails 4.0.0 application starting in development on http://0.0.0.0:3000

This most likely means Rack::Lock is used in your test.

I used the following command rails s puma -e production

Rack::Lock was removed as a default in Rails 4.