Determines the number of connection slots that are reserved for connections by PostgreSQL superusers. At most max_connections connections can ever be active simultaneously. Whenever the number of active concurrent connections is at least max_connections minus
superuser_reserved_connections, new connections will be accepted only for superusers, and no new replication connections will be accepted.
The default value is three connections. The value must be less than the value of max_connections. This parameter can only be set at server start.