Either way we start out with no barriers after the initial startup. Barrier slaves propogate all of their persistent barriers to the barrier master. The master rebuilds its barrier database and sends any updates to any slaves which seem to need it. Any non-persistent barriers are destroyed. Once the barrier state is rebuilt, the barrier master opens up for new business and instructs all slaves to do likewise.
First thing is to tell clients about destroyed barriers, of course.
At some point we will now get round to the cluster recovery barrier request.