CREATE DATABASE dbname;
CREATE USER username WITH PASSWORD 'user_password';
GRANT ALL PRIVILEGES ON DATABASE "dbname" to username;

Dodatkowo dla PostgreSQL 15.x i nowszych:

ALTER DATABASE dbname OWNER TO username;

Źródło: https://stackoverflow.com/questions/74110708/postgres-15-permission-denied-for-schema-public

PostgreSQL 9.2 i nowsze:

SELECT pg_terminate_backend(pg_stat_activity.pid)
FROM pg_stat_activity
WHERE pg_stat_activity.datname = 'TARGET_DB'
  AND pid <> pg_backend_pid();

PostgreSQL 9.1 i starsze:

SELECT pg_terminate_backend(pg_stat_activity.procpid)
FROM pg_stat_activity
WHERE pg_stat_activity.datname = 'TARGET_DB'
  AND procpid <> pg_backend_pid();

Dwie metody:

sudo -u postgres -i
pg_ctl reload

sudo -u postgres -i
psql
SELECT pg_reload_conf();

Źródło: https://www.heatware.net/databases/postgresql-reload-config-without-restarting/