It makes sense to use Oracle Restart on Master and Standby with ADG or is that oversized.


Oracle Restart typically makes sense for any customer not running full RAC because it limits downtime and lets you manage multiple components (listener, db, asm etc) as one. Its just easier to manage services rather than all the discrete components. In this particular instance, depends on your plans for ADG. If your plans are for a full failover solution, then Oracle Restart is strongly recommended, otherwise for just (say) offloading reporting etc, it still makes sense but you could live without it.

does the observer(s) have to run on a third computer

For full robustness, we recommend to keep it out of both data centers. When that is absolutely not possible, you have can one in each data center, but that’s not the best practice.