Let's return to the problems faced by a single-machine RDBMS. We have seen how sharding can be employed as one method to scale relational databases horizontally in order to optimize costs as data grows for small- to medium-sized databases. However, the issue with sharding is that each node acts in a standalone manner with no knowledge of the other nodes in the cluster, meaning that a custom broker is required to both partition the data across the shards and to process read and write requests.
Distributed data stores, on the other hand, work out of the box as a single logical unit spanning a cluster of nodes.
Note that a data store is just a general term used to describe any type of repository used to persist data. ...
