Index selection in MongoDB 3.0 for $or query
I asked this question on the Google group for Mongodb. See Dwight's explanation and work around.

https://groups.google.com/forum/?__hstc=21977188.535555756f91d668db0d32d8604f6233.1443211966594.1443211966594.1443211966594.1&amp;__hssc=21977188.11.1443211966594&amp;__hsfp=469890013#!topic/mongodb-user/iKtaqA5KrKY

Thanks!