Postgresql fixed template for unicorn.rb to use with Capistrano deployment recipe

unicorn.rb

# This file has been generated from unicorn_template.rb.erb which is greatly inspired from:
# https://github.com/ricodigo/ricodigo-capistrano-recipes/blob/master/generators/unicorn.rb.erb
#
# See http://unicorn.bogomips.org/Unicorn/Configurator.html for complete
# documentation.

# Local variables
old_pid = '<%= unicorn_pid + ".old" %>'

# Unicorn setup

worker_processes <%= unicorn_workers %>
timeout <%= unicorn_workers_timeout %>

# Listen on a Unix data socket
listen '<%= unicorn_socket %>', :backlog => 1024
pid '<%= unicorn_pid %>'

user '<%= unicorn_user %>', '<%= unicorn_group %>'

# Help ensure your application will always spawn in the symlinked
# "current" directory that Capistrano sets up.
working_directory '<%= "#{deploy_to}/current" %>'

stderr_path '<%= "#{logs_path}/unicorn.stderr.log" %>'
stdout_path '<%= "#{logs_path}/unicorn.stdout.log" %>'

preload_app true

before_fork do |server, worker|
  # the following is highly recomended for Rails + "preload_app true"
  # as there's no need for the master process to hold a connection
  if defined?(ActiveRecord::Base)
    ActiveRecord::Base.connection.disconnect!
  end

  # Before forking, kill the master process that belongs to the .oldbin PID.
  # This enables 0 downtime deploys.
  old_pid = "/tmp/unicorn.my_site.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
end

after_fork do |server, worker|
  # the following is *required* for Rails + "preload_app true",
  if defined?(ActiveRecord::Base)
    ActiveRecord::Base.establish_connection
  end

  # if preload_app is true, then you may also want to check and
  # restart any other shared sockets/descriptors such as Memcached,
  # and Redis.  TokyoCabinet file handles are safe to reuse
  # between any number of forked children (assuming your kernel
  # correctly implements pread()/pwrite() system calls)
end

I was having problems with Postgresql getting confused about the different unicorn worker processes. Every few clicks on the website would generate a "prepared statement already exists" error. This forked config file seems to fix the problem for me. Each unicorn worker process will have its own connection to postgres.