Rails 3.1 / mysql2 error : “MySQL server has gone away”

Question

I\'m experiencing trouble upgrading my rails 2.3.14 / ruby 1.8.7 app to 3.1.1/1.9.2 : I have some

(ActiveRecord::StatementInvalid) \"Mysql2::Error: MySQL se         


        

Answer 1

Ok, I think I solved my problem. I didn't notice it when I posted my question, but it seemed that the error was timeout related : after about 20s, activerecord losts its connection.

$ rails runner "sleep 23; puts ActiveRecord::Base.connection.active?"
=> true
$ rails runner "sleep 25; puts ActiveRecord::Base.connection.active?"
=> false

So I dug further and I realized that mysql and mysql2 gems didn't deal with the MySQL 'wait_timeout' param the same way : mysql gem doesn't set it thus uses the MySQL default value 28800, whereas mysql2 gem sets it at 2592000 if not defined in the database.yml. But I have the impression that the value 2592000 is over the max value for this param : 2147483 ! Which could lead to the unexpected behavior I described...

I build a script test showing the bug : https://gist.github.com/1514154

And if I had some apparently random disconnect while loading rails console (cf my question), I think it's because of my app taking a long time to load and me sometimes waiting a few seconds before typing my command.

I can't explain why we are so few to encounter this problem. Perhaps it's specific to my conf (remote database, MySQL version ?). I've tried with another remote staging database : the bug didn't reproduce...

So as a conclusion, I will set wait_timeout: 2147483 in my database.yml. And maybe pull request rails...

Answer 2

Had a lot of lost connections - but I couldn't say if they went away due to the following tweak or elsewise :/

Had to throw the following script into initializers and add a line of configuration to each of my databases in my database.yml like this:

...
flags: <%= 65536 | 131072 %>
...

The script looks like this:

/config/initializers/mysql2.rb

module ActiveRecord
  class Base
    # Overriding ActiveRecord::Base.mysql2_connection
    # method to allow passing options from database.yml
    #
    # Example of database.yml
    #
    #   login: &login
    #     socket: /tmp/mysql.sock
    #     adapter: mysql2
    #     host: localhost
    #     encoding: utf8
    #     flags: 131072
    #
    # @param [Hash] config hash that you define in your
    #   database.yml
    # @return [Mysql2Adapter] new MySQL adapter object
    #
    def self.mysql2_connection(config)
      config[:username] = 'root' if config[:username].nil?

      if Mysql2::Client.const_defined? :FOUND_ROWS
        config[:flags] = config[:flags] ? config[:flags] | Mysql2::Client::FOUND_ROWS : Mysql2::Client::FOUND_ROWS
      end

      client = Mysql2::Client.new(config.symbolize_keys)
      options = [config[:host], config[:username], config[:password], config[:database], config[:port], config[:socket], 0]
      ConnectionAdapters::Mysql2Adapter.new(client, logger, options, config)
    end
  end
end