MySQL server has gone away fix

connection_fix.rb

# If your workers are inactive for a long period of time, they'll lose
# their MySQL connection.
#
# This hack ensures we re-connect whenever a connection is
# lost. Because, really. why not?
#
# Stick this in RAILS_ROOT/config/initializers/connection_fix.rb (or somewhere similar)
#
# From:
#   http://coderrr.wordpress.com/2009/01/08/activerecord-threading-issues-and-resolutions/
#   https://gist.github.com/1276131/e2b02748173eb0fc5cfed80a9d9c01df6264f8db

unless $LOADED_FEATURES.include?(__FILE__)
  $LOADED_FEATURES << __FILE__
  if ActiveRecord::ConnectionAdapters.const_defined?(:MysqlAdapter)
    module ActiveRecord::ConnectionAdapters
      class MysqlAdapter
        alias_method :execute_without_retry, :execute
    
        def execute(*args)
          execute_without_retry(*args)
        rescue ActiveRecord::StatementInvalid, Mysql::Error => e
          if e.message =~ /server has gone away/i
            warn "Server timed out, retrying"
            reconnect!
            retry
          else
            raise e
          end
        end
      end
    end
  elsif ActiveRecord::ConnectionAdapters.const_defined?(:Mysql2Adapter)
    module ActiveRecord::ConnectionAdapters
      class Mysql2Adapter
        alias_method :execute_without_retry, :execute
    
        def execute(*args)
          execute_without_retry(*args)
        rescue ActiveRecord::StatementInvalid, Mysql2::Error => e
          if e.message =~ /server has gone away/i
            warn "Server timed out, retrying"
            reconnect!
            retry
          else
            raise e
          end
        end
      end
    end
  end
end

I was getting Mysql::Error instead of ActiveRecord::StatementInvalid since Rails 3. See also: brianmario/mysql2#213