A lot :)

config/puma.rb

@@ -2,34 +2,32 @@
 # are invoked here are part of Puma's configuration DSL. For more information
 # about methods provided by the DSL, see https://puma.io/puma/Puma/DSL.html.
 
-# Puma can serve each request in a thread from an internal thread pool.
-# The `threads` method setting takes two numbers: a minimum and maximum.
-# Any libraries that use thread pools should be configured to match
-# the maximum value specified for Puma. Default is set to 5 threads for minimum
-# and maximum; this matches the default thread size of Active Record.
-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'
-  require 'concurrent-ruby'
-  worker_count = Integer(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'
+# Puma starts a configurable number of processes (workers) and each process
+# serves each request in a thread from an internal thread pool.
+#
+# The ideal number of threads per worker depends both on how much time the
+# application spends waiting for IO operations and on how much you wish to
+# to prioritize throughput over latency.
+#
+# As a rule of thumb, increasing the number of threads will increase how much
+# traffic a given process can handle (throughput), but due to CRuby's
+# Global VM Lock (GVL) it has diminishing returns and will degrade the
+# response time (latency) of the application.
+#
+# The default is set to 3 threads as it's deemed a decent compromise between
+# throughput and latency for the average Rails application.
+#
+# Any libraries that use a connection pool or another resource pool should
+# be configured to provide at least as many connections as the number of
+# threads. This includes Active Record's `pool` parameter in `database.yml`.
+threads_count = ENV.fetch("RAILS_MAX_THREADS", 3)
+threads threads_count, threads_count
 
 # Specifies the `port` that Puma will listen on to receive requests; default is 3000.
-port ENV.fetch('PORT') { 3000 }
-
-# Specifies the `environment` that Puma will run in.
-environment ENV.fetch('RAILS_ENV') { 'development' }
-
-# Specifies the `pidfile` that Puma will use.
-pidfile ENV.fetch('PIDFILE') { 'tmp/pids/server.pid' }
+port ENV.fetch("PORT", 3000)
 
 # Allow puma to be restarted by `bin/rails restart` command.
 plugin :tmp_restart
+
+# Only use a pidfile when requested
+pidfile ENV["PIDFILE"] if ENV["PIDFILE"]