Shard-level Replication

In Oracle Globally Distributed Database a shard is a database. The availability of a shard is not affected by an outage or slowdown of one or more shards. Oracle Data Guard replication can be used to provide individual shard-level high availability. Replication is automatically configured and deployed when the distributed database is created.

Oracle Data Guard is tightly integrated with Oracle Globally Distributed Database to provide high availability and disaster recovery with strict data consistency and zero data loss. Oracle Data Guard replication maintains one or more synchronized copies (standbys) of a shard (the primary) for high availability and data protection. Standbys can be deployed locally or remotely, and when using Oracle Active Data Guard can also be open for read-only access.

See Shard-Level Replication with Oracle Data Guard for more information.

Optionally, you can use Oracle RAC for shard-level high availability, complemented by replication, to maintain shard-level data availability in the event of a cluster outage. Each shard can be deployed on an Oracle RAC cluster to give it instant protection from node failure. For example, each shard could be a two node Oracle RAC cluster. Oracle Globally Distributed Database automatically fails over database connections from a shard to its replica in the event of an unplanned outage.

Raft Replication

Instead of replication at the shard level, the Raft replication feature in Oracle Globally Distributed Database creates smaller replication units and distributes them automatically among the shards to handle chunk assignment, chunk movement, workload distribution, and balancing upon scaling (addition or removal of shards), including planned or unplanned shard availability changes.

Raft replication is built into Oracle Globally Distributed Database to provide a consensus-based, high-performance, low-overhead availability solution, with distributed replicas and fast failover with zero data loss, while automatically maintaining the replication factor if shards fail. With Raft replication management overhead does not increase with the number of shards. If you are used to NoSQL databases and do not expect to know anything about how replication works, Oracle Globally Distributed Database native replication just works.

Unlike Data Guard replication, Raft replication does not need to be reconfigured when shards are added or removed, and replicas do not need to be actively managed.

See Raft Replication Configuration and Management for more information.