there is currently not so much things to configure in PostgreSQL from
systemd's service point of view (not taking postgresql.conf into account),
concretely, we configure PGPORT and PGDATA, from which the later is
important (and often re-configured to point e.g. to some dedicated mount
point, etc.). That tells systemd's unit file where it should start
PostgreSQL server from.
What does not seem to be quite 100% OK is that, when user wants to change
PGDATA, we instruct him to make a separate service file:
$ cat /etc/systemd/system/postgresql.service
This works OK -- but the problem is that it is quite too much for just
changing one simple directory path.
What seems to be better approach is to have real configuration file, such one
for which '$ rpm -qc postgresql-server' would not be quiet. Lets say:
$ cat /etc/postgresql/postgresql
With some additional packager's work, that allows us to do yet another
configuration easily - and that is multiple PostgreSQL running on one
single machine (on different ports or IPs). The only thing would be to
create yet another file:
$ cat /etc/postgresql/postgresql@com_example
$ systemctl start postgresql@com_example
Would you see something bad on that approach (please, take into account that
we would not stop supporting the old way, we just want to make future
configuration easier and straight-forward).