This subject was already discussed, this may help you : http://markmail.org/message/6dybhww56bxvufzf#query:+page:1+mid:6dybhww56bxvufzf+state:results
How many Column Families are one too many for Cassandra ?
I created a db with 5000 CFs (I can go into the reasons later) but the
latency seems to be very erratic now. Not sure if it is because of the
number of CFs.