Amazon CTO Werner Vogels says the best day of his year was when Amazon turned off its largest Oracle data warehouse

• On November 1, Amazon switched off its largest Oracle database and moved over to its own data warehouse, Redshift.
• Amazon CTO Werner Vogels said this was his happiest day at Amazon this year.
• Amazon plans to move completely off of Oracle's databases, but Oracle founder and CTO Larry Ellison pointed out that much of Amazon still relies on Oracle's software.

For Amazon CTO Werner Vogels, his best day of this year was November 1.

"This was the moment when we switched off one of the world's largest, if not the largest, Oracle data warehouse and moved it over to Redshift," Vogels said on stage Thursday at Amazon Web Services' annual conference.

Redshift is Amazon's own data warehouse. CNBC previously reported that Amazon plans to completely move off of Oracle's databases by 2020.

Oracle founder and CTO Larry Ellison scoffed at the idea, as Amazon has spent millions on Oracle databases this year. "It's kind of embarrassing when Amazon uses Oracle but they want you to use Aurora and Redshift," Ellison said. "They've had 10 years to get off Oracle, and they're still on Oracle."

In early November, AWS CEO Andy Jassy tweeted that Amazon's Consumer business turned off its Oracle data warehouse, and the plan is to have 88 percent of Oracle databases moved to Amazon's own.

In the past six months, Redshift has become 3.5 times faster, Vogels said.

"There have been enormous improvements in real-world workloads," Vogels said.

Read more: Amazon Web Services CEO Andy Jassy roasted Larry Ellison by turning the Oracle founder into a cartoon-like face peeking over a wall