It's possible that my diagnosis of the exact problem is wrong, and that it's not the symlink
but something else which offends SELinux. All I can say is that /var/lib/pgsql/base being a
directory owned by the postgres user works perfectly, but /var/lib/pgsql/base being a symlink
to a directory owned by the postgres user on another filesystem does not. Postgres can be
started after a "setenforce 0" so it's certain that SELinux is the problem. I honestly have
no idea where this particular SELinux policy originates, or is expressed. But I do know that
it seems to have been known to postgres developers since at least 2005.
The same topic, from 2006, on the Fedora list: