Comment 1 for bug 1495125

An update. Now t it *is* known what would be more preferable for Openstack apps (Oslo.messaging library) - lost state.
While reordering and duplicated delivery of messages is a major threat for current state of OpenStack apps relying on Oslo.messaging rpc calls, which is only at-most-once, and seem never be at-least-once. More details here https://blueprints.launchpad.net/oslo.messaging/+spec/at-least-once-guarantee