walreceiver uses a temporary replication slot by default

walreceiver uses a temporary replication slot by default

If no permanent replication slot is configured using
primary_slot_name, the walreceiver now creates and uses a temporary
replication slot.  A new setting wal_receiver_create_temp_slot can be
used to disable this behavior, for example, if the remote instance is
out of replication slots.

Reviewed-by: Masahiko Sawada <masahiko.sawada@2ndquadrant.com>
Discussion: https://www.postgresql.org/message-id/CA%2Bfd4k4dM0iEPLxyVyme2RAFsn8SUgrNtBJOu81YqTY4V%2BnqZA%40mail.gmail.com