> Other alternative is self-learning bitmap
(
http://ect.bell-labs.com/who/aychen/sbitmap4p.pdf) which, in my
understanding, is more memory efficient when counting small values.
In another thread on the Cassandra mailing list the topic of
self-learning bitmap's for cardinality estimation came up (thanks
Yuki!). This isn't one I've previously encountered during literature
search. Does anyone have any experience with them?