Searching MOS Note on dynamic sampling

I colleague of mine told me that he read a MOS Note that was describing the details of the way dynamic sampling is done. The note was mentioning that only bitmap blocks  are sampled and blocks less than 25% full are considered empty. In that same note also deferred segment creation is mentioned. As my colleague is very experienced I believe is memory is correct. However, we cannot find that note any more.

Can somebody point us to the doc?

Regards and thank

Lothar