Shares of Oracle Corp. dipped in trading Tuesday, on rumors that two major customers – Amazon and Salesforce – are building software to help them transition off its proprietary database software.

San Francisco-based Salesforce.com is building an Oracle database alternative codenamed “Sayonara,” while Amazon has moved two systems underpinning its e-commerce operations to open-source, NoSQL-based database software, The Information reported, citing multiple unnamed sources.

Both Amazon.com and Salesforce are longtime customers of Redwood City-based Oracle, a fact that billionaire cofounder Larry Ellison routinely brings up. Both have grown, they’ve expanded beyond e-commerce and customer relationship management systems into cloud-based enterprise software – in some cases, in direct competition with Oracle.

“Let me tell you who’s not moving off of Oracle, a company you’ve heard of that gave us another $ 50 million … this quarter to buy Oracle Database and other Oracle technologies. That company is Amazon,” Ellison said on an earnings call in December. “They’re not moving off of Oracle. Salesforce is not moving off of Oracle. Our competitors, who have no reason to like us very much, continue to invest in and run their entire business on Oracle.”

On the same call, Ellison took a shot at Amazon’s cloud-based database alternative, Redshift, saying the 4-year-old project still could not compete with Oracle’s industry-leading database software.

“… It costs you 5x more to run Redshift than to run the Oracle Autonomous,” he said at the time. “… This is not total cost of ownership. This is not labor. This is your Amazon bill, what you pay Amazon to do a piece of work you can run on the Oracle Cloud and pay 20 cents on the dollar by moving from Amazon to Oracle. “

If Salesforce and Amazon are able to build credible alternatives to Oracle’s database software, it could provide a path for other large companies interested in making similar a move. Oracle has owned the database software market since the 1990s.