Interesting. My reading of the 9.4 docs[1][2] is that set_config can't be used to change one-off settings that require a server restart, such as wal_level. It also doesn't seem to be able to change the config file at all. Is there some way to do that?

I'd also like to know more about how superusers can overwrite files. Do you have a link?

[1] http://www.postgresql.org/docs/9.4/static/functions-admin.ht... [2] http://www.postgresql.org/docs/9.4/static/runtime-config-wal...