The event notification mechanism includes server and client components. An event can be posted by using the server component. The server component broadcasts event messages to interested client applications.
An application can get messages using a client component. This component is the Sql_messenger ActiveX control. The control allows client application to receive messages for specific event. You can easy build much more sophisticated applications or services using these components. Now, in awaiting some critical data or events an application does not need to query PostgreSQL repeatedly. The PostgreSQL will notify an application when the specific data is coming or event happens.
The user application is able to get messages without an established PostgreSQL connection.
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