Question

我正在尝试为在Ubuntu服务器上运行的Rails 3.1应用程序设置一个守护进程。就像这样简单：

require File.expand_path('../../config/environment',  __FILE__)
require 'rubygems'
require 'daemons'

Daemons.run_proc('my_script') do
  loop do
    puts BlogPost.count
    sleep(5)
  end
end

但是当我到达BlogPost.count时，我收到以下错误：

/usr/lib/ruby/gems/1.8/gems/activerecord-3.1.0/lib/active_record/connection_adapters/mysql2_adapter.rb:283:in `query': Mysql2::Error: MySQL server has gone away: SHOW FIELDS FROM `blog_posts` (ActiveRecord::StatementInvalid)
from /usr/lib/ruby/gems/1.8/gems/activerecord-3.1.0/lib/active_record/connection_adapters/mysql2_adapter.rb:283:in `execute'
from /usr/lib/ruby/gems/1.8/gems/activerecord-3.1.0/lib/active_record/connection_adapters/abstract_adapter.rb:244:in `log'
from /usr/lib/ruby/gems/1.8/gems/activesupport-3.1.0/lib/active_support/notifications/instrumenter.rb:21:in `instrument'
from /usr/lib/ruby/gems/1.8/gems/activerecord-3.1.0/lib/active_record/connection_adapters/abstract_adapter.rb:239:in `log'
from /usr/lib/ruby/gems/1.8/gems/activerecord-3.1.0/lib/active_record/connection_adapters/mysql2_adapter.rb:283:in `execute'
from /usr/lib/ruby/gems/1.8/gems/activerecord-3.1.0/lib/active_record/connection_adapters/mysql2_adapter.rb:473:in `columns'
from /usr/lib/ruby/gems/1.8/gems/activerecord-3.1.0/lib/active_record/connection_adapters/abstract/connection_pool.rb:95:in `initialize'
from /usr/lib/ruby/gems/1.8/gems/activerecord-3.1.0/lib/active_record/connection_adapters/abstract/connection_pool.rb:185:in `with_connection'
from /usr/lib/ruby/gems/1.8/gems/activerecord-3.1.0/lib/active_record/connection_adapters/abstract/connection_pool.rb:92:in `initialize'
from /usr/lib/ruby/gems/1.8/gems/activerecord-3.1.0/lib/active_record/base.rb:706:in `call'
from /usr/lib/ruby/gems/1.8/gems/activerecord-3.1.0/lib/active_record/base.rb:706:in `default'
from /usr/lib/ruby/gems/1.8/gems/activerecord-3.1.0/lib/active_record/base.rb:706:in `[]'
from /usr/lib/ruby/gems/1.8/gems/activerecord-3.1.0/lib/active_record/base.rb:706:in `columns'
from /usr/lib/ruby/gems/1.8/gems/activerecord-3.1.0/lib/active_record/base.rb:722:in `column_names'
from /usr/lib/ruby/gems/1.8/gems/activerecord-3.1.0/lib/active_record/relation/calculations.rb:192:in `aggregate_column'
from /usr/lib/ruby/gems/1.8/gems/activerecord-3.1.0/lib/active_record/relation/calculations.rb:213:in `execute_simple_calculation'
from /usr/lib/ruby/gems/1.8/gems/activerecord-3.1.0/lib/active_record/relation/calculations.rb:187:in `perform_calculation'
from /usr/lib/ruby/gems/1.8/gems/activerecord-3.1.0/lib/active_record/relation/calculations.rb:155:in `calculate'
from /usr/lib/ruby/gems/1.8/gems/activerecord-3.1.0/lib/active_record/relation/calculations.rb:58:in `count'
from /usr/lib/ruby/gems/1.8/gems/activerecord-3.1.0/lib/active_record/base.rb:445:in `__send__'
from /usr/lib/ruby/gems/1.8/gems/activerecord-3.1.0/lib/active_record/base.rb:445:in `count'
from script/background_job_processor_control.rb:22

知道为什么我的脚本无法连接MySQL吗？如果我将BlogPost.count代码放在Daemons.run_proc之前，我可以很好地连接到MySQL。

----------编辑：解决了！ ------------

对于任何对解决方案充满好奇的人，我必须做三件事才能让它发挥作用：

在启动/停止我的守护程序时包含bundle exec：RAILS_ENV=production bundle exec myscript.rb start。
此时我停止了MySQL2错误，但开始收到记录器错误。解决方案是在run_proc块中添加以下代码：ActiveRecord::Base.logger = ActiveSupport::BufferedLogger.new('/path/to/log/file.log')
然后我遇到第三个错误，解决方案是要求run_proc块内的Rails环境而不是脚本中的早期。

我的最终脚本如下所示：

require 'rubygems'
require 'daemons'

Daemons.run_proc('my_script') do 
  require File.expand_path('../../config/environment',  __FILE__)
  ActiveRecord::Base.logger = ActiveSupport::BufferedLogger.new('/path/to/log/file.log')
  loop do
    puts BlogPost.count
    sleep(5)
  end
end

Answer 1

要正确预加载脚本的Rails环境（依赖项），请按以下步骤启动它：

bundle exec my_script_ctl start

Answer 2

我不知道为什么，但是当我在守护脚本之前断开数据库连接时，它会起作用，例如：

# app env
ENV['RAILS_ENV'] = 'production'
require File.expand_path(File.dirname(__FILE__) + "/../config/environment")

# disconnect first
ActiveRecord::Base.connection.disconnect!

# Become a daemon
Daemons.daemonize

# connect again
ActiveRecord::Base.establish_connection ENV['RAILS_ENV']

# ... do what you need

希望这有帮助。

Rails 3.1 + Daemons gem不允许我访问我的数据库

2 个答案: