Use worker count equal to processor count in production (rails#46838)

Author: dhh

railties/lib/rails/generators/rails/app/templates/config/puma.rb.tt

@@ -11,6 +11,12 @@ max_threads_count = ENV.fetch("RAILS_MAX_THREADS") { 5 }
 min_threads_count = ENV.fetch("RAILS_MIN_THREADS") { max_threads_count }
 threads min_threads_count, max_threads_count
 
+# Specifies that the worker count should equal the number of processors in production.
+if ENV["RAILS_ENV"] == "production"
+  worker_count = ENV.fetch("WEB_CONCURRENCY") { Concurrent.physical_processor_count }
+  workers worker_count if worker_count > 1
+end
+
 # Specifies the `worker_timeout` threshold that Puma will use to wait before
 # terminating a worker in development environments.
 worker_timeout 3600 if ENV.fetch("RAILS_ENV", "development") == "development"