There is a small inconsistency:
select time '12:30:57.123456789';
gives
12:30:57.123457
but
select make_time(12, 30, 57.123456789);
gives
12:30:57.123456
From:
Andrew Dunstan Date: Subject:
Re: ALTER SYSTEM SET command to change postgresql.conf parameters
(RE: Proposal for Allow postgresql.conf values to be changed via
SQL [review])