A decade ago, it was a serious question whether open source databases were ready for mission-critical applications. The obvious response at the time was “no,” with substantial evidence to back that claim. More recently, self-promoting vendors have continued to pitch the idea that proprietary databases “are the best fit for mission-critical applications,” but the idea has lost credibility.

Particularly because “95% of mainstream IT organizations use open-source software in their mission-critical IT portfolios,” according to Gartner. The other 5%? They won’t be around long enough to figure out the reason for holding out.

The reason? In databases, Gartner continues, “open source options are leading innovative efforts.” In other words, if you want to be on the cutting edge, today you must use open source databases. You don’t always have to pay for them, however, and that’s the biggest problem for legacy vendors like Oracle.

‘Free’ gets paid

While still nowhere near as large as the roughly $34 billion traditional database market, Gartner pegs the size of the open source database market at $2.6 billion, or 7.6% of the overall market. More importantly, that open source piece grew 100% from 2014-2015, and another 50% from 2015-2016. While Gartner has not yet released data for 2017, odds are good that open source databases will maintain close to 50% growth.

Of course, open source being open source, the vast majority of adoption doesn’t register on the income statement of any particular company. By Gartner’s estimation, a mere 1-5% of the open source database user base shows up as paid customers.

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In other words, the value of the open source database market to customers/users is measured in the tens of billions, or even hundreds of billions, of dollars. One other way of thinking about this? That’s tens or hundreds of billions of dollars that proprietary vendors will never capture.

The risk to the old guard

As such, even as the open source database market dramatically outpaces the traditional market in revenue growth (50% in 2016 vs. 7.7%), the unpaid adoption of open source databases arguably cuts into the earning potential of Oracle, IBM, and Microsoft even more than the paid adoption does. Granted, Oracle and IBM have figured out how to make some money on open source databases (upwards of $100 million each, according to Gartner).

AWS, however, makes much more, raking in nearly $750 million. In this brave new world of open source databases, AWS is out-monetizing Oracle on Oracle’s home turf (MySQL), putting it in a position to displace Oracle at the top of the database heap over time.

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“The greatest force in legacy databases is inertia,” Gartner analyst Merv Adrian once told me. That inertia will keep Larry Ellison in yachts for many years to come.

But cracks are forming in the database dynasties of the old guard. In 2011, the top five database vendors (Oracle, Microsoft, IBM, SAP, Teradata) controlled 91% of the revenue. In 2016 that number had declined to 86.9%. Meanwhile, Oracle’s market share has declined every year since 2013, by Gartner’s reckoning. Open source databases, whether run on-premises or in the cloud, are starting to take their toll, one that actually hurts far more when companies elect to not pay for them.