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Keep in mind the article was written in 2014. I was at Amazon until near the end of 2013 and we were actively migrating off of oracle at that time, but it was no where near ready when I left.

Amazon still runs on Oracle ERP. Even though they removed Oracle databases from AWS and other internal orgs, their own financials are still run in Oracle EBS. Thus the data for all the books bought by a person might still be in Oracle

Any Oracle implementation at Amazon certainly could not scale to do this real-time.

Black Friday, and Oracle's inability to scale up to meet it without explosive licensing costs, is a major factor in Amazon's decision to remove Oracle from their sales systems.

...that we are aware of

Sure. The same applies to lizard overlords running the world.