[ovn] transaction error: {"details":"Transaction causes multiple rows in \"MAC_Binding\" table to have identical values

[Michal Nasiadka]

In Kolla-Ansible OVN CI we noticed following entries in OVN Controller logs:

2020-03-21T11:41:45.067Z|00013|ovsdb_idl|WARN|transaction error: {"details":"Transaction causes multiple rows in \"MAC_Binding\" table to have identical values (\"lrp-0bf65362-bb2e-41e0-8ee9-fbff0d063221\" and \"::\") for index on columns \"logical_port\" and \"ip\". First row, with UUID 31fe10d5-989a-4631-a07d-008c30a5f665, existed in the database before this transaction and was not modified by the transaction. Second row, with UUID 6ea1e391-1efa-403f-9399-9d33815c2d74, was inserted by this transaction.","error":"constraint violation"}
17 2020-03-21T11:41:45.067Z|00014|main|INFO|OVNSB commit failed, force recompute next time.

Link to Zuul build logs:
CentOS8:
https://zuul.opendev.org/t/openstack/build/48a2db8d271c4b8bb305d108c34e4e07/log/primary/logs/kolla/openvswitch/ovn-controller.txt#16
https://zuul.opendev.org/t/openstack/build/48a2db8d271c4b8bb305d108c34e4e07/log/

Ubuntu:
https://zuul.opendev.org/t/openstack/build/c118f9e862e247468360fa78d1409833/log/primary/logs/kolla/openvswitch/ovn-controller.txt#18
https://zuul.opendev.org/t/openstack/build/c118f9e862e247468360fa78d1409833/log/

[Maciej Jozefczyk (maciejjozefczyk)]

I saw it a few times but I haven't found why.

[Reason li (lireason)]

Verify that two gateways are added to the router. This happens when one interface is bound to a gateway chassis and another interface is bound to a gateway chassis.