DynamoDB Hash and Range

Hash doesn't have to be unique if "Hash and Range" PK is selected. In this case, it is used for evenly sharding the data under-the-hood.

However, the Hash and Range combination should be unique (not mentioned specifically but obvious and implied).

More details in the following references:

• http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/DataModel.html
• http://stackoverflow.com/questions/10938727/dynamodb-how-is-the-hash-key-used