Comment 5 for bug 1282925

@armax

Thanks for sharing information.
The stacktraces are exactly same as what I experienced.

What do you think about removing transaction from delete_port"s"?
I think we don't need to delete all ports under one transaction.
It is used only by release_dhcp_ports at the moment, and each dhcp port can be deleted separately.

It is row risk and I believe we can get a good behavior.