What is limit of QVD size & how we can optimize the over sized QVD
As far as I am aware there is no physical limit on the size of your QVD. In order to create a QVD though the data first has to be in memory - so the amount of RAM you have is a limiting factor. Given the excellent compression that QlikView brings though it is generally not an issue.
Recently I was working on a QVD with 180 million rows, and forty odd dimensional columns.
Regarding optimising QVD's, I have written a blog post that covers this very topic: http://bit.ly/YnAMqT
Hope that is of use.
According to release notes, if you try load more than 2,147,483,647 unique values into QV, it won't work properly. So it can be a parameter, even if a QVD file could store more records than this, it won't be possible to load them completely in QlikView. Not to mention that 2,147,483,647 is quite a lot of data.