This error log is coming continuously with mitaka gbp code. Once restarted neutron-server it resolved the exception.
2016-12-22 03:24:44.502 31566 ERROR oslo_messaging.rpc.dispatcher [req-32962028-22d1-4426-9f79-91e62454a7fa - - - - -] Exception during message handling: This Session's transaction has been rolled back by a nested rollback() call. To begin a new transaction, issue Session.rollback() first.
2016-12-22 03:24:44.502 31566 ERROR oslo_messaging.rpc.dispatcher Traceback (most recent call last):
2016-12-22 03:24:44.502 31566 ERROR oslo_messaging.rpc.dispatcher File "/usr/lib/python2.7/site-packages/oslo_messaging/rpc/dispatcher.py", line 138, in _dispatch_and_reply
2016-12-22 03:24:44.502 31566 ERROR oslo_messaging.rpc.dispatcher incoming.message))
2016-12-22 03:24:44.502 31566 ERROR oslo_messaging.rpc.dispatcher File "/usr/lib/python2.7/site-packages/oslo_messaging/rpc/dispatcher.py", line 183, in _dispatch
2016-12-22 03:24:44.502 31566 ERROR oslo_messaging.rpc.dispatcher return self._do_dispatch(endpoint, method, ctxt, args)
2016-12-22 03:24:44.502 31566 ERROR oslo_messaging.rpc.dispatcher File "/usr/lib/python2.7/site-packages/oslo_messaging/rpc/dispatcher.py", line 127, in _do_dispatch
2016-12-22 03:24:44.502 31566 ERROR oslo_messaging.rpc.dispatcher result = func(ctxt, **new_args)
2016-12-22 03:24:44.502 31566 ERROR oslo_messaging.rpc.dispatcher File "/usr/lib/python2.7/site-packages/opflexagent/rpc.py", line 238, in ip_address_owner_update
2016-12-22 03:24:44.502 31566 ERROR oslo_messaging.rpc.dispatcher self.gbp_driver.ip_address_owner_update(context, **kwargs)
2016-12-22 03:24:44.502 31566 ERROR oslo_messaging.rpc.dispatcher File "/usr/lib/python2.7/site-packages/gbpservice/neutron/services/grouppolicy/drivers/cisco/apic/apic_mapping.py", line 820, in ip_address_owner_update
2016-12-22 03:24:44.502 31566 ERROR oslo_messaging.rpc.dispatcher ports_to_update = self.update_ip_owner(kwargs['ip_owner_info'])
2016-12-22 03:24:44.502 31566 ERROR oslo_messaging.rpc.dispatcher File "/usr/lib/python2.7/site-packages/gbpservice/neutron/services/grouppolicy/drivers/cisco/apic/apic_mapping.py", line 413, in update_ip_owner
2016-12-22 03:24:44.502 31566 ERROR oslo_messaging.rpc.dispatcher return super(ApicMappingDriver, self).update_ip_owner(ip_owner_info)
2016-12-22 03:24:44.502 31566 ERROR oslo_messaging.rpc.dispatcher File "/usr/lib/python2.7/site-packages/apic_ml2/neutron/db/port_ha_ipaddress_binding.py", line 129, in update_ip_owner
2016-12-22 03:24:44.502 31566 ERROR oslo_messaging.rpc.dispatcher ipa, network_id or port['network_id'])
2016-12-22 03:24:44.502 31566 ERROR oslo_messaging.rpc.dispatcher File "/usr/lib/python2.7/site-packages/apic_ml2/neutron/db/port_ha_ipaddress_binding.py", line 61, in get_port_for_ha_ipaddress
2016-12-22 03:24:44.502 31566 ERROR oslo_messaging.rpc.dispatcher models_v2.Port.network_id == network_id).first()
2016-12-22 03:24:44.502 31566 ERROR oslo_messaging.rpc.dispatcher File "/usr/lib64/python2.7/site-packages/sqlalchemy/orm/query.py", line 2634, in first
2016-12-22 03:24:44.502 31566 ERROR oslo_messaging.rpc.dispatcher ret = list(self[0:1])
2016-12-22 03:24:44.502 31566 ERROR oslo_messaging.rpc.dispatcher File "/usr/lib64/python2.7/site-packages/sqlalchemy/orm/query.py", line 2457, in __getitem__
2016-12-22 03:24:44.502 31566 ERROR oslo_messaging.rpc.dispatcher return list(res)
2016-12-22 03:24:44.502 31566 ERROR oslo_messaging.rpc.dispatcher File "/usr/lib64/python2.7/site-packages/sqlalchemy/orm/query.py", line 2736, in __iter__
2016-12-22 03:24:44.502 31566 ERROR oslo_messaging.rpc.dispatcher return self._execute_and_instances(context)
2016-12-22 03:24:44.502 31566 ERROR oslo_messaging.rpc.dispatcher File "/usr/lib64/python2.7/site-packages/sqlalchemy/orm/query.py", line 2749, in _execute_and_instances
2016-12-22 03:24:44.502 31566 ERROR oslo_messaging.rpc.dispatcher close_with_result=True)
2016-12-22 03:24:44.502 31566 ERROR oslo_messaging.rpc.dispatcher File "/usr/lib64/python2.7/site-packages/sqlalchemy/orm/query.py", line 2740, in _connection_from_session
2016-12-22 03:24:44.502 31566 ERROR oslo_messaging.rpc.dispatcher **kw)
2016-12-22 03:24:44.502 31566 ERROR oslo_messaging.rpc.dispatcher File "/usr/lib64/python2.7/site-packages/sqlalchemy/orm/session.py", line 905, in connection
2016-12-22 03:24:44.502 31566 ERROR oslo_messaging.rpc.dispatcher execution_options=execution_options)
2016-12-22 03:24:44.502 31566 ERROR oslo_messaging.rpc.dispatcher File "/usr/lib64/python2.7/site-packages/sqlalchemy/orm/session.py", line 910, in _connection_for_bind
2016-12-22 03:24:44.502 31566 ERROR oslo_messaging.rpc.dispatcher engine, execution_options)
2016-12-22 03:24:44.502 31566 ERROR oslo_messaging.rpc.dispatcher File "/usr/lib64/python2.7/site-packages/sqlalchemy/orm/session.py", line 313, in _connection_for_bind
2016-12-22 03:24:44.502 31566 ERROR oslo_messaging.rpc.dispatcher self._assert_active()
2016-12-22 03:24:44.502 31566 ERROR oslo_messaging.rpc.dispatcher File "/usr/lib64/python2.7/site-packages/sqlalchemy/orm/session.py", line 218, in _assert_active
2016-12-22 03:24:44.502 31566 ERROR oslo_messaging.rpc.dispatcher "This Session's transaction has been rolled back "
2016-12-22 03:24:44.502 31566 ERROR oslo_messaging.rpc.dispatcher InvalidRequestError: This Session's transaction has been rolled back by a nested rollback() call. To begin a new transaction, issue Session.rollback() first.
2016-12-22 03:24:44.502 31566 ERROR oslo_messaging.rpc.dispatcher
