Ruby - Exception occured: [Mysql2::Error] closed MySQL connection

Question

I have a Rails application now only runs internally, so there's not so much visits right now. And there're two resque worker running hardly to fetch data from the web and inserts into a mysql database, every insert will followed by sleep 10 second.

We run it on a VPS. After like every 5 hours, I will encounter an Exception Exception occured: [Mysql2::Error] closed MySQL connection".

What could be the reason causing the exception? Now the pool size is 5.

Will it help if I raise the pool size and specify reconnect: true in my database.yml?

Answer 1

This is a common issue when using the mysql2 gem version 0.2.11 or below in combination with multithreading. There is a bug on the issue tracker with a details on the problem but in conclusion the advice is to:

1. Update the gem version you are using to >= 0.2.12
2. Add the reconnect: true option your db connection config in the database.yml file

You probably already solved your problem but this might help others who come across this question.

Answer 2

If your workers are inactive for a long period of time, they'll lose their MySQL connection.

see here for the solution

or just stick this in an initializer

unless Rails.env.to_s == 'test'
  module ActiveRecord::ConnectionAdapters
    class Mysql2Adapter
      alias_method :execute_without_retry, :execute

    def execute(*args)
      execute_without_retry(*args)
      rescue Exception => e
        if e.message =~ /server has gone away/i
          warn "Server timed out, retrying"
          reconnect!
          retry
        else
          raise e
        end
      end
    end
  end
end