The following query, give six differents kind of context presents on the
system view pg_settings, that list all postgresql current parameters
setting.

postgres=# select distinct context from pg_settings;
context

backend
internal
postmaster
sighup
superuser
user
(6 rows)

What's the mean for 'backend', 'postmaster' and 'sighup' context of a
parameter? How i can know if a parameter is modifiable only with a
server restart, rather than a 'pg_ctl reload' (sighup?) or a "SET/ALTER
USER/ALTER DATABASE" command?

Best regards,
Francesco.