Every upgrade of Oracle software or even just the installation of a patch carries the risk that the behavior of the Oracle product used will change. With a major upgrade, i.e. increasing the version from 12c to 18c, for example, there is a high probability that there will be behavioral changes in one place or another that should be examined in more detail beforehand. A good starting point for this is the New Features and Database Upgrade Guide . With the latter, the chapter "Behavior Changes, Deprecated and Desupported Features" should be given particular attention.
The main danger, however, is with changes that are not officially documented in the Oracle documentation or in the My Oracle Support Portal. In many belarus telegram screening cases, a My Oracle Support Note is created after the first occurrence of a change in behavior and a resulting service request from an affected Oracle customer. To ensure a certain level of security for the update process, the quarterly updates should be thoroughly tested beforehand or only installed with a delay. With the latter approach, the My Oracle Support Portal or relevant Oracle blogs should be searched for clues before installing the patch.
A positive example of behavioral changes that are disabled by default are the Optimizer Fixes . Optimizer Fixes can significantly change the behavior of the Optimizer and should be tested thoroughly before activation. Otherwise, performance problems can be the result.