MongoDB Shard considering DBRefs

Question

I have a case where in first collection I use DBRef to another collection. First collection is Books, the second is Users (who read those books). The user can have avatars and various other informations, which is reasonable to keep in separate collection. But now I need to shard the books collection. If I shard it amongst 2 nodes, how the Users collection will be sharded? I would like to keep users that are related to particular books in same node. Is that possible? Thanks!

Answer 1

At the moment this is not possible out side of tag aware sharding ( http://docs.mongodb.org/manual/core/tag-aware-sharding/ ). Kristina (when she was still with 10gen) wrote a good article on how to distribute your data, can easily be used to group multiple collections: http://www.kchodorow.com/blog/2012/07/25/controlling-collection-distribution/

However, you might find that very difficult to maintain as such I wouldn't advise it unless you are solely a DBA since you will literally be spending most of your time keeping it together with an ever expanding network like that.

What I would do instead is shard the books on user_id and then shard the user collection on hashed _id that way you only need to query two shards at most