Copy important changes from unicorn.rb.example to

unicorn.rb.example.development. Also remove unneeded configurations
and update the comment accordingly. I think REE was long dead.

config/unicorn.rb.example

@@ -67,11 +67,11 @@ pid "/home/git/gitlab/tmp/pids/unicorn.pid"
 stderr_path "/home/git/gitlab/log/unicorn.stderr.log"
 stdout_path "/home/git/gitlab/log/unicorn.stdout.log"
 
-# combine Ruby 2.0.0dev or REE with "preload_app true" for memory savings
-# http://rubyenterpriseedition.com/faq.html#adapt_apps_for_cow
+# Save memory by sharing the application code among multiple Unicorn workers
+# with "preload_app true". See:
+# https://www.rubydoc.info/gems/unicorn/5.1.0/Unicorn%2FConfigurator:preload_app
+# https://brandur.org/ruby-memory#copy-on-write
 preload_app true
-GC.respond_to?(:copy_on_write_friendly=) and
-  GC.copy_on_write_friendly = true
 
 # Enable this flag to have unicorn test client connections by writing the
 # beginning of the HTTP headers before calling the application.  This

config/unicorn.rb.example.development

@@ -1,7 +1,15 @@
 worker_processes 2
 timeout 60
 
+preload_app true
+check_client_connection false
+
 before_fork do |server, worker|
+  # the following is highly recommended 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 /darwin/ =~ RUBY_PLATFORM
     require 'fiddle'
 
@@ -13,3 +21,12 @@ before_fork do |server, worker|
   end
 end
 
+after_fork do |server, worker|
+  # Unicorn clears out signals before it forks, so rbtrace won't work
+  # unless it is enabled after the fork.
+  require 'rbtrace' if ENV['ENABLE_RBTRACE']
+
+  # the following is *required* for Rails + "preload_app true",
+  defined?(ActiveRecord::Base) and
+    ActiveRecord::Base.establish_connection
+end