upgrade to repmgr3

hi!

I have been using postgres 9.4 and repmgr2.0 combination and been doing
replication (hot standby). Now I'd like to start doing slot based
replication and have installed repmgr3 and exeuted the provided sql scripts
and also added use_replication_slots=1 into repmgr.conf.

The question is that what is the correct procedure to switch into using
slots (max_replication_slots) in this case as the system has been set up
already without them? Do I have to unregister and re-register all the
standbys? Hopefully re-clone could be avoided.

What I tried was that I configured max_replication_hosts=5, restarted
master, created some slots using select * from
pg_create_physical_replication_slot(<name>), configured one created slot
into recovery.conf in the slave. What I noticed was that replication seemed
to be still working after this but in repl_nodes table slot_name remained
empty. Then I did standby re-register with force and slot_name was filled
with repmgr_slot_2 value which is not the name I gave for the slot. I think
repmgr invented this name but in the pg_replication_slots table
repmgr_slot_2 does not exist. There is only the slot I created myself
(active=t). So I guess this approach is not quite right.

What if I just skip doing the re-register. Does is matter if slot_name
remains empty in repl_nodes?

br,
Pekka