At a high level, SQL queries use statistics and other variables to determine what execution plan to run. As a result, a given SQL statement (SQL ID) may end up having multiple execution plans (hash plans) over time. Depending on the execution plan selected at runtime, performance can improve or degrade accordingly.

Security is one of those things that keeps DBAs awake at night, particularly if they are not following best practices and staying up to date with the latest security patches.

In this blog series, I will go through the full process of a database version upgrade and an architecture update. I will also discuss lessons learned and a few tips I gathered during this endeavor.

See [Part 1] History Command: Tips and Tricks for Your 12.2 Oracle Database Upgrade.

This is completely understandable. Anything that changes the underlying architecture of a database system is sure to cause undue stress and apprehension.