I want my database (SQL) to notify or push updates to client application

Question

I was developing this application on VB.net 2010 and SQL 2008.
I wanted the clients to be notified for updates on the db, and the application u

Answer 1

Query Notification will push to a Service Broker service, not directly to your application. See The Mysterious Notification to understand how it works. Your application is waiting for notifications by posting a WAITFOR(RECEIVE) statement on the database. Which implies that each of the 100 clients is occupying one SQL Server worker thread (which are limited, see max worker threads option). I've seen this working in production with +1000 clients (after bumping up the max worker threads option) but I would advise against it.

My recommendation would be to have one service monitoring for change, using SqlDependency/QueryNotifications. This service would then push notifications, using WCF for instance, to all your running apps. You would subscribe to generic changes (the table Foo was changed), not to specific ones (the row x in table Foo was inserted).

As a general rule SqlDependency/Query Notifications can only inform you that data has changed, but it won't push the new data. The application must refresh its local datasets by running the queries again, once notified.