DBAs biggest fears I’d guess are Optimizer Wrong Query Results bugs as usually the optimizer does not write a message into the alert.log saying “Sorry, I was in a bad mood today …”.
The Oracle Database Optimizer is a complex piece – and in Oracle 12c it delivers great performance results. Plus (my personal experience when you know what to do) it is more predictable which I like a lot when changing databases from one to another release. But due to its complexity sometimes we see issues – and sometimes it is necessary to switch off tiny little pieces …
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