Oracle GDS provides the following key capabilities for a set of replicated databases that are globally distributed or located within the same data center.
I implemented this architectural solution for a large financial company to meet their 99.99% SLA database uptime requirements.
Here is a short video showing a Java script using UCP connecting through GDS to two backend Oracle databases.
As an example the video below depicts how we used gdsctl to relocate the Oracle service to the other database and the Java script will also flip over with FAN events that via UCP connections. The end result … connections automatically continue on the surviving database automatically.
An Oracle Database and Cloud Blog Site 