I cannot find documentation about the algorithm that mongodb uses for collection or fragment keys.
Can someone help with this or post a link?
If you are more interested in how indexing generally works, check out this presentation on internal elements: http://www.mongodb.com/presentations/storage-engine-internals or this http://www.mongodb.com/presentations/mongodbs -storage-engine-bit-bit
As a single fragment does not know much about the entire structure of the cluster, it uses the same indexing algorithm inside, only there is a metadata layer that knows which datapart is associated with a particular fragment.
, : http://docs.mongodb.org/manual/core/indexes/ , , (DOCS). , sharding.check
, : md5, : https://github.com/mongodb/mongo/blob/master/src/mongo/db/hasher.cpp
: https://github.com/mongodb/mongo/blob/master/src/mongo/util/md5.cpp
, , https://github.com/mongodb/mongo/blob/master/src/mongo/db/index/hash_access_method.cpp.
http://docs.mongodb.org/manual/core/sharded-clusters/
"" , :
http://docs.mongodb.org/manual/core/sharded-cluster-operations/