Oracle bought 2 companies which develop 2 open source storage engines that MySQL uses. Those storage engines are both transactional.
There’s the possibility Oracle does the stupid (from a PR perspective) move of making those databases proprietary. But it’s OPEN SOURCE right now. Which means that it’ll branch.
Worst case scenario? The developing stops here, and InnoDB and BDB never get any more functional than they currently are.
The “bad” scenario? MySQL is a company. With hired staff. They pay the hired staff to get familiar with the source code for those engines and continue to develop them. Hence the branch.
The likely scenario? 1) Oracle tries to have a pluggable storage engine architecture like MySQL. Oracle Express or Lite or whatever would be free with those engines, pay with the original. 2) Oracle tries to go on the good partnership of “we support MySQL by developing their architecture, we’re so nice, buy our product.”
Really, everyone is worried over nothing. The whole point of open source is that it’s open! Once you go open, you can close later on and people still have something to work with.