I am unable to understand the role equi-depth histograms play in query optimization. Can someone please give me some pointers to good resources or could anyone explain. I have read a few research papers but still I could not convince my for the need and use of equi-depth histograms. So, can someone please explain equi-depth histograms with an example.

Also can we merge the buckets of the histograms so that the histogram becomes small enough and fits in 1 page on disk?

Also what are bucket boundaries in equi-depth histograms?