L2GW LogicalSwitch tunnel is not created after executed l2gateway connection creation command.
Command executed: neutron l2-gateway-connection-create
Performed 100 times and only succeeded once.

Environment details:
OpenStack Version：stable/ocata
ODL Version：Carbon-FR + patch
patch: https://git.opendaylight.org/gerrit/#/c/56773/
https://git.opendaylight.org/gerrit/#/c/56710/
HWVTEP: Open vSwitch 2.6.1 HWVTEP Emulator
: HA Cluster

The following logs are found in Karaf.log
2017-06-08 14:45:45,804 | ERROR | -dispatcher-7716 | TransactInvokerImpl | 292 - org.opendaylight.ovsdb.hwvtepsouthbound-impl - 1.4.0.Carbon | HWVTEP transaction operation failed referential integrity violation Table Ucast_Macs_Remote column locator row 3ba6a92d-52a0-46e3-ae41-dedb95da8e74 references nonexistent row 00000000-0000-0000-0000-000000000000 in table Physical_Locator.
2017-06-08 14:45:45,804 | ERROR | -dispatcher-7716 | TransactInvokerImpl | 292 - org.opendaylight.ovsdb.hwvtepsouthbound-impl - 1.4.0.Carbon | Failed transaction update [vlan_bindings :

{2222=f7617bb2-98ca-4ba0-9c61-94df217e29c6}

, ]insert [encapsulation_type : vxlan_over_ipv4 , dst_ip : 10.0.0.10 , ] insert [locators : [PhysicalLocator_Random_8b95ac7a75414bfeaed47dc246aeadda] , ] insert [locator_set : PhysicalLocatorSet_Random_82148b021d94464bb06049e90e1b4e67 , logical_switch : f7617bb2-98ca-4ba0-9c61-94df217e29c6 , MAC : unknown-dst , ] insert [logical_switch : f7617bb2-98ca-4ba0-9c61-94df217e29c6 , MAC : fa:16:3e:ea:8b:fe , ]

Cause of failure:
'locator' is not specified for 'insert [logical_switch : f7617bb2-98ca-4ba0-9c61-94df217e29c6 , MAC : fa:16:3e:ea:8b:fe , ]'.
I think this caused the failure of insert operation of Ucast_Macs_Remote table.

When tunnel was created successfully, there were two transactions in ovsdb.
And 'locator' was specified and insert operation of Ucast_Macs_Remote table was succeed at that time.
1. the 1st transaction
update [vlan_bindings :

{2222=53968c22-9106-4f5e-9d3b-84713fe3bda7}

, ]
insert [encapsulation_type : vxlan_over_ipv4 , dst_ip : 10.0.0.10 , ]
insert [locators : [PhysicalLocator_Random_5aa0854faa6d42169564a904de0d45d9] , ]
insert [locator_set : PhysicalLocatorSet_Random_4812e00980db4d68909451b1fe94db8a , logical_switch : 53968c22-9106-4f5e-9d3b-84713fe3bda7 , MAC : unknown-dst , ]
2. the 2nd transaction
insert [locator : 00d1ef47-faf1-4d63-8f52-ad4121d9a235 , logical_switch : 53968c22-9106-4f5e-9d3b-84713fe3bda7 , MAC : fa:16:3e:58:ba:81 , ]