Explanation/Reference:
Replication Nodes are organized into shards. A shard contains a single Replication Node which is responsible for performing database writes, and which copies those writes to the other Replication Nodes in the shard. This is called the master node. All other Replication Nodes in the shard are used to service read-only operations.
Note: Oracle NoSQL Database provides multi-terabyte distributed key/value pair storage that offers scalable throughput and performance. That is, it services network requests to store and retrieve data which is organized into key-value pairs.
References: https://docs.oracle.com/cd/E26161_02/html/GettingStartedGuide/introduction.html