In discussing vacuum_truncate_set it occurs to me there is no SQL way for someone to easily view the current setting (or unset status) of a reloption. Seems like we could modify SHOW to cover this use case. It is mostly redundant with \d+ which already distinguishes unset and set options by displaying the later, but being SQL and more explicit seems to at least make considering extending SHOW worthwhile. An unset reloption specified here could then have its computed value displayed and annotated.
