Asynchronous Notification PostgreSQL Prev Chapter 40. No additional information is passed from the notifier to the listener. Thus, typically, any actual data that needs to be communicated is transferred through the relation. However, the communication from the backend to the frontend is not asynchronous.
Notification comes piggy-backed on other query results.
Thus, an application must submit queries, even empty ones, in order to receive notice of backend notification. In effect, the libpq application must poll the backend to see if there is any pending notification information. After the execution of a query, a frontend may call PQNotifies to see if any notification data is available from the backend. PQNotifies returns the notification from a list of unhandled notifications from the backend. Returns NULL if there are no pending notifications from the backend.