Database setup:
RAILS_ENV=production bin/rake db:create
RAILS_ENV=production bin/rake db:migrate
Run the server (threaded with Puma):
bin/rails s -e production
Using an ab concurrency of 1 works as expected:
ab -n 300 -c 1 http://localhost.dev:3000/
Specifying concurrent requests causes logging to halt before ab finishes:
ab -n 300 -c 6 http://localhost.dev:3000/
The issue happens with activerecord-session_store loaded.
Without rails_12factor it's necessary to use tail -f log/production.log, which does appear to work with an ab concurrency of 6.
I also tried using sqlite instead of pg but it was still working (sometimes?).