Question

I working with a big database what is the best way in performance -connected mode or disconnected mode- should I use?

Answer 1

quoted from the post specified above: What's better: DataSet or DataReader?

It depends on your needs. One of the most important differences is
that a DataReader will retain an open connection to your database
until you’re done with it while a DataSet will be an in-memory object.
If you bind a control to a DataReader then it’s still open. In
addition, a DataReader is a forward only approach to reading data that
can’t be manipulated. With a DataSet you can move back and forth and
manipulate the data as you see fit.

Hope this helps