ASP.NET,avoiding unnecessary async AJAX postbacks

I have faced an issue trying to avoid unnecessary async postbacks.

First of all, improve the website asp.net performance - e.g. avoid using updates by design (e.g. markup or default UpdateMode="always" behaviour),instead use UpdateMode="Conditional" and even consider ChildrenAsTriggers="false".

In this manner one will be able to minimize the need for updating specific update panels and thus posting back dummy markup and causing flicker applying them.

So far, so good, I am able to tell if e.g. updUpdatepanel1 is to be updated by my code and the very same for updUpdatepanel2. I could even check if an UpdatePanel is being updated or not with some little tricks.

But I could not find any means to:

• check if no update is pending (on server side) and cancel the postback
  currently I am experimenting with Response.End.
• cancel only one updatepanel at a later point and cause only a small part of the page to be partially rendered....