pgsql: Set fallback_application_name for a walreceiver to cluster_name

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(at)timbira(dot)com(dot)br>
Discussion: https://www.postgresql.org/message-id/flat/1257eaee-4874-e791-e83a-46720c72cac7(at)2ndquadrant(dot)com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/6ae578a91e653ce3f4cba8cab96ce41e0cc7103f

Modified Files
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doc/src/sgml/config.sgml | 14 +++++++++++---
src/backend/replication/walreceiver.c | 2 +-
2 files changed, 12 insertions(+), 4 deletions(-)