Re: allow online change primary_conninfo

Hi

> If you do that, the startup process would try to jump to a different
> source to fetch WAL if archiving is enabled. Is that really what we
> want?

Yes, similar behavior with exit walreceiver by any reason. Same as in all previous patch versions.
(not sure this can be changed in some small and elegant way)

> It would be nice to have one message for primary_conninfo being
> updated, and one for primary_slot_name so as if both are changed at
> the same time the user gets the correct information.

Hm, maybe even better would be separate message if both settings are changed? Doing this in attached patch.

> "In a moment starts streaming WAL with new configuration." sounds
> strange. It would be more natural to have something like "The WAL
> receiver is going to be restarted with the new configuration", just a
> suggestion.

This phrase was proposed here: https://www.postgresql.org/message-id/20181213.184233.215171075.horiguchi.kyotaro%40lab.ntt.co.jp
My english is poor, so i added message just as proposed. I replaced to your variant.

regards, Sergei