Merge remote-tracking branch 'upstream/pull/5299'

[rails.git] / config / puma.rb

diff --git a/config/puma.rb b/config/puma.rb
index 5ed44377449e9c5102f0ac5ab01c646097886a70..60e1b9c67a0b17400eee7a22935d1cf6312f5ae9 100644 (file)
--- a/config/puma.rb
+++ b/config/puma.rb
@@ -1,38 +1,33 @@
-# 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
+# This configuration file will be evaluated by Puma. The top-level methods that
+# 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.
 
-# Specifies the `port` that Puma will listen on to receive requests; default is 3000.
+# Puma starts a configurable number of processes (workers) and each process
+# serves each request in a thread from an internal thread pool.
 #
-port        ENV.fetch("PORT") { 3000 }
-
-# Specifies the `environment` that Puma will run in.
+# 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.
 #
-environment ENV.fetch("RAILS_ENV") { "development" }
-
-# Specifies the `pidfile` that Puma will use.
-pidfile ENV.fetch("PIDFILE") { "tmp/pids/server.pid" }
-
-# Specifies the number of `workers` to boot in clustered mode.
-# Workers are forked web server processes. If using threads and workers together
-# the concurrency of the application would be max `threads` * `workers`.
-# Workers do not work on JRuby or Windows (both of which do not support
-# processes).
+# 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.
 #
-# workers ENV.fetch("WEB_CONCURRENCY") { 2 }
-
-# Use the `preload_app!` method when specifying a `workers` number.
-# This directive tells Puma to first boot the application and load code
-# before forking the application. This takes advantage of Copy On Write
-# process behavior so workers use less memory.
+# The default is set to 3 threads as it's deemed a decent compromise between
+# throughput and latency for the average Rails application.
 #
-# preload_app!
+# 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)
 
-# Allow puma to be restarted by `rails restart` command.
+# 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"]