postgresql_hacks/change_settings.md

How to reload config changes during the runtime (SIGHUP)?

select pg_reload_conf();

Does changing a config setting require a restart of postgresql or just a reload (SIGHUP)?

This can be archived by simply selecting the setting from pg_settings.

select context from pg_settings where name='max_wal_size';

Is a restart of postgresql required?

select pending_restart from pg_settings where name='max_wal_size';

This will tell you if a restart is pending for a setting.