About 2 years ago (time is flying) I explained how I did the same to support range queries over "n" attributes, the method ended up being in the book "MongoDB,

About 2 years ago (time is flying) I explained how I did the same to support range queries over "n" attributes, the method ended up being in the book "MongoDB, the Definitive Guide" by Chodorow and Dirolf (O'Reilly): http://chemeo.com/doc/technology http://chemeo.com/doc/technology (Search for "Indexing For High Speed Search" to skip non MongoDB related information).