Quote Originally Posted by wysota View Post
If you call setUniformRowHeights(true) then there is no such effect. I can scroll the view very quickly.
- forgot to set setUniformRowHeights(true), Its working fine now

- The only & main issue I have now is, rowCount() is still calling for all the top level items , Any idea how to prevent it.?

By the way, I don't think you calculated the memory use correctly. For 10M top-level items with 2 child items each the application uses over 600MB for the data segment.
Sorry I ran 32-bit application, It is taking around 280MB in a same case.