MySQL adapter doesn't reconnect on lost connection

I've had this happen to me before in production on edge Rails awhile back. I'm not sure why the old behavior was kicked out though, but in practice it definitely doesn't reconnect all the time.

And yup I can confirm that the LOST_CONNECTION_ERROR_MESSAGES constant is not being used anywhere in AR code.

The retry-magically code was removed as it was dangerous. You could easily end up resubmitting an insert statement and duplicating data.

However the dispatcher in rails pre-verifies connections in production mode too, which version are you seeing this with?

This was in 2.1.2 - is the dispatcher pre-verifying connections 2.2 or is it already in 2.1.x?

The verification in 2.1 has an optimisation that you might be hitting:

verify_active_connections in connection_specifications.rb uses a timeout. Make sure you haven't set that:

    cattr_accessor :verification_timeout, :instance_writer => false
    @@verification_timeout = 0

But the logic is:

      # Lazily verify this connection, calling <tt>active?</tt> only if it hasn't
      # been called for +timeout+ seconds.
      def verify!(timeout)
        now = Time.now.to_i
        if (now - @last_verification) > timeout
          reconnect! unless active?
          @last_verification = now
        end
      end

So that should be working fine. In 2.2 we remove that setting and just always verify the connection.