atlasapi/atlas-persistence — pull request #107 by tfm (2013-10-05 13:23:49+00:00)
Title: Only do lookup queries on the primary when writing content, not during other API actions 

It turns out that read preference, when set on a DBCollection, applies across the board, since DBCollections are shared (see com.mongodb.DBApiLayer.doGetCollection()).

Instead we must set the read preference on each find() within MongoLookupEntryStore. More error prone, but I don't see another way around the shared DBCollection objects.