This is a regression related to CASSANDRA-4858
Range queries are taking orders of magnitude more time to complete than before because the query planner is frequently unable to calculate the correct intersection of contiguous ranges for a given node.
For example, SELECT * FROM TBL should result in exactly one scan at CL.ONE when RF = #nodes when in fact it can result in several hundred scans (sometimes thousands). The problem is exasperated with vnodes.
The regression occurred at some point between 2.0.4 (which works fine) and 2.0.9.