The following documentation comment has been logged on the website:
Page: https://www.postgresql.org/docs/10/static/archive-recovery-settings.html
Description:
Documentation for restore_command in recovery.conf only says, "This
parameter is required for archive recovery, but optional for streaming
replication," but it doesn't say specifically when the restore_command
string will be used and why. My guess is that as long as the WAL files are
still available on the master (primary) host, the recovery will fetch them
via the replication slot, but if a WAL is missing on the primary, only then
will the restore_command be used. But this isn't explicitly stated. It could
be that the restore_command is always used, even if the WAL file is still
available on the primary.
