Actually, Amazon is kind of sharding their database: They encapsulate every kind of data into a program that manages it:
>What I mean by that is that within Amazon, all small pieces of business functionality are run as a separate service. For example, this availability of a particular item is a service that is a piece of software running somewhere that encapsulates data, that manages that data.
>What I mean by that is that within Amazon, all small pieces of business functionality are run as a separate service. For example, this availability of a particular item is a service that is a piece of software running somewhere that encapsulates data, that manages that data.
(see http://queue.acm.org/detail.cfm?id=1388773)