tweak unicorn config

Author: Albert Yi

config/unicorn/production.rb

@@ -4,9 +4,9 @@
 # Set unicorn options
 worker_processes 22
 
-preload_app true
 timeout 180
-listen "127.0.0.1:9000"
+listen "127.0.0.1:9000", :tcp_nopush => true
+listen "/tmp/.unicorn.sock", :backlog => 64
 
 # Spawn unicorn master worker for user apps (group: apps)
 user 'albert', 'albert'
@@ -24,20 +24,56 @@
 # Set master PID location
 pid "#{app_path}/tmp/pids/unicorn.pid"
 
+# combine Ruby 2.0.0+ with "preload_app true" for memory savings
+preload_app true
+
+# Enable this flag to have unicorn test client connections by writing the
+# beginning of the HTTP headers before calling the application.  This
+# prevents calling the application for connections that have disconnected
+# while queued.  This is only guaranteed to detect clients on the same
+# host unicorn runs on, and unlikely to detect disconnects even on a
+# fast LAN.
+check_client_connection false
+
+# local variable to guard against running a hook multiple times
+run_once = true
+
 before_fork do |server, worker|
-  old_pid = "#{server.config[:pid]}.oldbin"
-  
-  if File.exists?(old_pid) && server.pid != old_pid
-    begin
-      Process.kill("QUIT", File.read(old_pid).to_i)
-    rescue Errno::ENOENT, Errno::ESRCH
-      # someone else did our job for us
-    end
-  end
+  # the following is highly recomended for Rails + "preload_app true"
+  # as there's no need for the master process to hold a connection
+  defined?(ActiveRecord::Base) and ActiveRecord::Base.connection.disconnect!
 
-  if defined?(ActiveRecord::Base)
-    ActiveRecord::Base.connection.disconnect!
+  # Occasionally, it may be necessary to run non-idempotent code in the
+  # master before forking.  Keep in mind the above disconnect! example
+  # is idempotent and does not need a guard.
+  if run_once
+    # do_something_once_here ...
+    run_once = false # prevent from firing again
   end
+
+  # The following is only recommended for memory/DB-constrained
+  # installations.  It is not needed if your system can house
+  # twice as many worker_processes as you have configured.
+  #
+  # # This allows a new master process to incrementally
+  # # phase out the old master process with SIGTTOU to avoid a
+  # # thundering herd (especially in the "preload_app false" case)
+  # # when doing a transparent upgrade.  The last worker spawned
+  # # will then kill off the old master process with a SIGQUIT.
+  # old_pid = "#{server.config[:pid]}.oldbin"
+  # if old_pid != server.pid
+  #   begin
+  #     sig = (worker.nr + 1) >= server.worker_processes ? :QUIT : :TTOU
+  #     Process.kill(sig, File.read(old_pid).to_i)
+  #   rescue Errno::ENOENT, Errno::ESRCH
+  #   end
+  # end
+  #
+  # Throttle the master from forking too quickly by sleeping.  Due
+  # to the implementation of standard Unix signal handlers, this
+  # helps (but does not completely) prevent identical, repeated signals
+  # from being lost when the receiving process is busy.
+  sleep 1
 end
 
 after_fork do |server, worker|