Set fallback_application_name for a walreceiver to cluster_name
By default, the fallback_application_name for a physical walreceiver
is "walreceiver". This means that multiple standbys cannot be
distinguished easily on a primary, for example in pg_stat_activity or
synchronous_standby_names.
If cluster_name is set, use that for fallback_application_name in the
walreceiver. (If it's not set, it remains "walreceiver".) If someone
set cluster_name to identify their instance, we might as well use that
by default to identify the node remotely as well. It's still possible
to specify another application_name in primary_conninfo explicitly.
Reviewed-by: Euler Taveira <euler@timbira.com.br>
Discussion: https://www.postgresql.org/message-id/flat/
1257eaee-4874-e791-e83a-
46720c72cac7@2ndquadrant.com