Update puma config.

Procfile

@@ -1 +1 @@
-web: bundle exec puma -p $PORT -e $RACK_ENV -t 0:5
+web: bundle exec puma -C config/puma.rb

config/puma.rb

@@ -0,0 +1,18 @@
+workers Integer(ENV['PUMA_WORKERS'] || 3)
+threads Integer(ENV['MIN_THREADS']  || 1), Integer(ENV['MAX_THREADS'] || 16)
+
+preload_app!
+
+rackup      DefaultRackup
+port        ENV['PORT']     || 3000
+environment ENV['RACK_ENV'] || 'development'
+
+on_worker_boot do
+  # worker specific setup
+  ActiveSupport.on_load(:active_record) do
+    config = ActiveRecord::Base.configurations[Rails.env] ||
+                Rails.application.config.database_configuration[Rails.env]
+    config['pool'] = ENV['MAX_THREADS'] || 16
+    ActiveRecord::Base.establish_connection(config)
+  end
+end