从 sqlite3 切换到 mysql 后 ActiveRecord::ConnectionNotEstablished答案

【问题标题】：ActiveRecord::ConnectionNotEstablished after switching to mysql from sqlite3从 sqlite3 切换到 mysql 后 ActiveRecord::ConnectionNotEstablished
【发布时间】：2012-08-23 03:31:48
【问题描述】：

我最近将我的 rails 数据库从 sqlite3 切换到了 mysql，并且在尝试访问我的服务器时遇到了 ConnectionNotEstablished 错误。

这是错误的完整堆栈跟踪。

ActiveRecord::ConnectionNotEstablished (ActiveRecord::ConnectionNotEstablished):
  activerecord (3.2.8) lib/active_record/connection_adapters/abstract/connection_pool.rb:404:in `retrieve_connection'
  activerecord (3.2.8) lib/active_record/connection_adapters/abstract/connection_specification.rb:170:in `retrieve_connection'
  activerecord (3.2.8) lib/active_record/connection_adapters/abstract/connection_specification.rb:144:in `connection'
  activerecord (3.2.8) lib/active_record/query_cache.rb:67:in `rescue in call'
  activerecord (3.2.8) lib/active_record/query_cache.rb:61:in `call'
  activerecord (3.2.8) lib/active_record/connection_adapters/abstract/connection_pool.rb:473:in `call'
  actionpack (3.2.8) lib/action_dispatch/middleware/callbacks.rb:28:in `block in call'
  activesupport (3.2.8) lib/active_support/callbacks.rb:405:in `_run__318842653__call__302530175__callbacks'
  activesupport (3.2.8) lib/active_support/callbacks.rb:405:in `__run_callback'
  activesupport (3.2.8) lib/active_support/callbacks.rb:385:in `_run_call_callbacks'
  activesupport (3.2.8) lib/active_support/callbacks.rb:81:in `run_callbacks'
  actionpack (3.2.8) lib/action_dispatch/middleware/callbacks.rb:27:in `call'
  actionpack (3.2.8) lib/action_dispatch/middleware/reloader.rb:65:in `call'
  actionpack (3.2.8) lib/action_dispatch/middleware/remote_ip.rb:31:in `call'
  actionpack (3.2.8) lib/action_dispatch/middleware/debug_exceptions.rb:16:in `call'
  actionpack (3.2.8) lib/action_dispatch/middleware/show_exceptions.rb:56:in `call'
  railties (3.2.8) lib/rails/rack/logger.rb:26:in `call_app'
  railties (3.2.8) lib/rails/rack/logger.rb:16:in `call' 
  actionpack (3.2.8) lib/action_dispatch/middleware/request_id.rb:22:in `call'
  rack (1.4.1) lib/rack/methodoverride.rb:21:in `call'
  rack (1.4.1) lib/rack/runtime.rb:17:in `call'
  activesupport (3.2.8) lib/active_support/cache/strategy/local_cache.rb:72:in `call'
  rack (1.4.1) lib/rack/lock.rb:15:in `call'
  actionpack (3.2.8) lib/action_dispatch/middleware/static.rb:62:in `call'
  railties (3.2.8) lib/rails/engine.rb:479:in `call'
  railties (3.2.8) lib/rails/application.rb:223:in `call'
  rack (1.4.1) lib/rack/content_length.rb:14:in `call'
  railties (3.2.8) lib/rails/rack/log_tailer.rb:17:in `call'
  rack (1.4.1) lib/rack/handler/webrick.rb:59:in `service'
  /home/aaron/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/webrick/httpserver.rb:138:in `service'
  /home/aaron/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/webrick/httpserver.rb:94:in `run'
  /home/aaron/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/webrick/server.rb:191:in `block in start_thread'

与数据库的连接似乎工作正常。我可以运行 db:migrate 并且它运行良好，以及 Rails 控制台，我可以访问数据和一切都很好。我注意到，当我启动时，错误的工作方式会因环境而略有不同。它似乎在测试中运行良好。在开发中，当我在浏览器中访问页面时会抛出错误，而在生产中，当我启动它时会抛出错误。

问题似乎与这里提出的问题几乎相同： Rails and MySQL - ActiveRecord::ConnectionNotEstablished in production environment, 但没有一个答案对我有用。

我把所有的代码都推到这里了：https://github.com/Aaronneyer/aaronneyer.com

【问题讨论】：

将 .sass-cache 添加到你的 .gitignore 中。

标签： mysql ruby-on-rails activerecord ruby-on-rails-3.2

【解决方案1】：

仍然不确定造成这种情况的确切原因，但我能够通过移除不再使用的 newrelic gem 来解决它。

【讨论】：

我花了数小时调试 Rake cron 作业（使用 PostgreSQL）中各种非常奇怪的 ActiveRecord 连接错误，并且想说谢谢，因为您的评论解决了我的问题。非常感谢！
你好 - 我为 New Relic 工作，并想说明我们已经在 newrelic_rpm gem 的 3.6.4 版本中解决了这个问题的根本原因。很抱歉给您带来了头痛！

【解决方案2】：

您同时设置了套接字和主机。选择一个，可能会解决您的问题。

【讨论】：

不，尝试只使用套接字和主机。每种情况都发生了同样的事情。