From the post:
I’m writing this up because there’s always quite a bit of discussion on both the Cassandra and Hector mailing lists about indexes and the best ways to use them. I’d written a previous post about Secondary indexes in Cassandra last July, but there are a few more options and considerations today. I’m going to do a quick run through of the different approaches for doing indexes in Cassandra so that you can more easily navigate these and determine what’s the best approach for your application.
Good article on indexes in Cassandra.