Oracle live data updates for frequently updated table: poll or CQN?
Polling isn't uncommon; it will depend on what your application and data latency requirements are. Depending on your infrastructure, it may not be possible to poll more than a few times per minute.
If you must have real-time, or as near as possible, you might be able to use Oracle Advanced Queues to stream the updates.

https://www.oracle.com/technetwork/database/features/data-integration/oracle-aq-tech-wp11-2-191324.pdf
https://docs.oracle.com/database/121/LNCPP/queuing.htm#LNCPP010.

It would be an extra cost, but one other alternative is Oracle GoldenGate:

https://www.oracle.com/middleware/technologies/goldengate.html